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Paper 1317 "Experimental ..... method for determ/ning flow quality during the expansion tube run period. Figure ...... time by Pergament (1963) _hieh follows. ...... and equilibrium conditions in shock tunnels. Report. I_pt. Physics,. Australian.

/H -39" NASA

Contractor

Report

191573

fo. /g/

Shock

Tunnel

Studies

Supplement

8

R. J. Stalker,

P. Hollis,

S. Tuttle,

D. Mee,

G. Kelly,

Phenomena

G. T. Roberts,

R. G. Morgan,

D. R. Buttsworth,

J. Simmons,

University St. Lucia,

G. A. Allen,

R. J. Bakos,

C. Brescianini,

of Scramjet

M. V. Pulsonetti,

K. Skinner, N. Ward,

and

L. Porter, A. Neely

of Queensland Queensland

Australia

(NASA-CR-191573)

Grant

NAGW-674

December

STUDIES SUPPLEMENT

1993

131

OF

SHOCK

TUNNEL

N94-23532

SCRAMJET PHENOMENA, 8 (Queensland Univ.)

p

Unclas

G3/34

n SA National Aeronautics Space Administration

and

Langley Research Center _ Hampton, Virginia 23681-0001

0203618

r

SitOCK NASA

TUNNEL GRANT

Following

STUDIES

NAGW

the

format

OF SCRAM

JET

674 - SUPPLEMENT of previous

PHENOMENA

1992

8

reports,

this

consists

of a series

of reports

projects, with a brief general introduction commenting on each report. follow the introduction in the order of the headings in the introduction. The projects are considered under funded jointly by NAGW 674 and Australian

sources

PROGRAM

specific

project

reports

the headings "Program A", corresponding to work Australian sources, and "Program B", funded from

alone.

A

(i)

Expansion

Tube Studies

(a)

Flow

the Diaphragm

near

_R.J. Stalker, This

The

on

P. Hollis,

started

of an Expansion

G.A.

Allen)

out to be a numerical

of determining

Tube

the minimum

study

length

of expansion

of driver

tube

required.

operation,

with

It soon became

the aim clear

that

the delay occasioned in opening the secondary diaphragm was a very important factor, and that this could not be estimated accurately, because of the flow through the opening The

diaphragm.

conclusion

model

reached

accurately,

Influence (G.T.

by the

consisting

that new emphasis

(b)

Therefore

increasing disturbances

pressure

(R.J. What

objective

the

was

that

steady

to techniques

flow

and unsteady

for pre-opening

Dia p_h___gm h on Flow Quali_"

study

of the effect

of diaphragm

diaphragm thickness may at the test section to occur

static pressure disturbances. deformation of the diaphragm

Mass

was

the main

of this project.

extremely

difficult

expansion.

to

It suggests

the diaphragm. in Expansion

Tubes

Roberts)

An experimental

(c)

study

of a mixed

be given

of Seconda_"

this became

and the upstream Loss of Te.st Gas

mass

A somewhat surprising has a beneficial effect

static

on the flow.

be expected earlier, as well

It showed

to cause as causing

pitot larger

that

pressure upstream

result was that allowing on both the downstream

prepitot

pressure.

in the Boundary

Layer

of an Expansion

Tube

Stalker) has

been

here.

This

layer,

thereby

compensate important

described

effect

involves

inducing for

as the

the

for practical

removal an

mass

"fountain of gas

extra

loss.

effect"

mass

from flow

It is found

flow conditions.

in expansion the in

that

test the

the

tubes

region

by the

downstream effect

is analysed

is not

boundary

direction likely

to to be

Thrust

Balance

(Sean

Tuttle)

This )'ear transverse

was spent in perfecting the "twisted sting" configuration bending modes and allowing thrust to be measured.

constructed, (iii)

and

Comparative Effects (R.J.

Development

subjected

Studies

of Oxygen Bakos,

to satisfactory

bench

Dissociation

on Hypen'elocity

appropriately choosing combustor duct pressure:: The diffcrence betxveen expected

to yield

(R.J.

Bakos

Sc_ramjet

in T4 and in ttypulse was in both facilities and, by

temperature

used.

Lower

inlet

temperatures

are

difference. Thrust

Production

scramjet combustor and nozzle thrust agreed v,ith computations.

were

tested

in T4.

It was

which

were

conducted

found

B

Scaling

and Jgnilion

(M.V. This

combustion was tested

R.G. Morgan)

An axisymmetric that the measured

PROGRAM

inlet

a greater

and

Experiments

test conditions, it could be arranged that measured were sensitive to dissociation enhanced heat release alone. the two facilities was small, but this was due to the

combustor

Axisymmetric

Combustion

& J. Tamagno)

A comparative experimental study involving continued. An identical combustor model

high

testing.

in T4 and lt,,_pu!se

R.G. Morgan

relatively

for removing the A nozzle has been

Effects

in Scram'el£_

Pulsonetti) is a more

combustion

considered

report

in a large

duct

on experiments

(48

mm

x 100

qualitative agreement with theory,, although order of magnitude less than predicted. lt_ersonic

Ignition

mm

x 1300

at low

pressure

mm).

in 1991

on

Results

were

in

delays

were

an

ignition

in a Scramjet

(A. Paull) Combustion

of Hydrogen

compared.

Ethane

enthalpies 1).

(_

Ethane

Modelling

yielded

12 Mj kg"),

may

suffer

of

predicting experimental

same

pressure

from mixing

Flow

using

rise

as Hydrogen

it at low stagnation limitations

various

than

at high stagnation

enthalpies

(_ 9 Mj kg

Hydrogen.

Turbulence

Models

and R. G. Morgan)

three the

the

but fell below

more

of a Scramjet

(C. Brescianini Testing

and of Ethane in a 27 mm x 54 mm x 800 mm duct were

turbulence

flow results

models,

in a scramjet accurately

of

increasing

combustor.

over the entire 2

None length

degree of

the

of

sophistication,

models

of the combustion

predicted duct.

by the

Shock

Interactions

,_ith

Hypersonic

and R.G.

Morgan)

Mixing

Layers

- Stead)'

Flow

Analysis

and

wave

vdth the

variable

Mach

number

flow

Experiments (D.R.

Buttsxvorth

A stud)' field

of the

produced

interaction by a mixing

A Time-of-flight (K. Skinner Results

of a shock

Mass

layer.

Spectrometer

for High Speed

Flows

and R.J. Stalker)

with a time-of-flight

is the detection

of driver

concentration.

However,

concentration

during

Measuring

the

_Hyperveloci_"

mass gas

in a shock

the

the test

effect

on

spectrometer

method flow

are presented.

tunnel, can

The

example

and the development

be applied

studied

of driver

to measurement

of

gas

species

period.

Drag

Aaroduced

by Nose

on

Bluntness

a Cone

in

Flow

(L. Porter, D. Mee and J. Simmons) This reports work on the extension of the stress wave effect of nose blunting on the drag of a slender cone. A Studx of Re_.nold's Skin Friction Gaug£ (G. Kelly,

A. Paull

Analog

in

Redistribution

Boundary

to measure

Laver

using

the

a new

and J. Simmons)

A comparison betv,een skin friction using the skin friction gauge ,xhich Ener_"

Hypersonic

balance

of Non

and heat transfer has been reported

Equilibrium

measurements previously.

Hvpervelocity

on a flat plate,

Flow

in a Scramjet

Duc____! (N. Ward and R.J. Stalker) Flow visualisation with calculations. Flow

Measurements

(A. Neely This flow limits

of nitrogen

flow

in a two dimensional

and Calibration

of a Superorbital

and

Expansion

comparison

Tube

and R.G. Morgan)

is a pilot stud)' of an expansion speeds in excess of 10 km.s". the value

produced

intake

of the diagnostics

at speeds

of 13 km.s _.

tube in a configuration aimed at producing Though the response of pressure transducers

used,

it appears

that a usable

test

flow

has

been

FLOW

NEAR

THE

(_ R.J. Stalker,

1.

DIAPHRAGM

P. tlollis

OF AN

and G.A.

EXPANSION

TUBE

Allen)

In

Introduction the

classical

diaphragm and the

of

expansion

tube

flow,

it

is

assumed

is instantaneously removed from the flow upon supersonic flow behind that shock is subjected

expansion

which

It is known different set

analysis

produces

that

the

in motion

finite

by

the

the shock

the

secondary

arrival of the primary shock, to a simple wave unsteady

the test flow. mass

to this, and a more

stationary,

that

of the secondary

sophisticated

arrival

of

reflects

the

as from

diaphragm

model

treats

primary

wall

cause

the diaphragm

shock.

a rigid

must

Since

and

flow

as a piston,

the

propagates

the

diaphragm

to be

which

is

is initially

upstream.

Then,

as the

diaphragm accelerates, expansion waves are generated These co_ntinually overtake the shock wave and weaken

which also propagate upstream. it until, after a sufficiently long

time,

the reflected

to reach

short

with respect

tube approaches delay' occasioned

wave

disappears.

to the overall

shock

operating

that produced by' the need

If the time

time

of the expansion

by the classical model, with to accelerate the diaphragm,

this state tube.

is sufficiently

then the flow

in the

the differences that there is a that the test gas close to the

diaphragm suffers an increase in entropy due to the reflected shock, and that this gas may also suffer a change in composition due to the same cause. The importance of these effects

depends

minimising The

purpose

consequence

how

much

of

the

present

of bringing

is impacted process

on

the model

by the primary

of acceleration,

shock,

gas

is affected,

the

allows

diaphragm

is to

a step closer it not only

it is also opening.

or the gradual

2.

test

investigation

the diaphragm, situation

of the

and

this can be minimised

separation

flow through

make

a preliminary

to physical moves

This

may

exploration

reality.

When

but also ruptures, take

the

form

of the "petalling"

of shattered

diaphragm.

Either

- it becomes

a "leaky'"

diaphragm,

and

Hueristic

of a free

diaphragm

(or

the of way

it is this

.A.nal,'sis to begin

by considering

the

motion

accelerating into a vacuum under the action of a pressure p. The diaphragm tube of constant area, which is infinitely long in both directions. Therefore, 1.,

there

undisturbed situation

is an

pressure which

i

PAGE BLANK

unsteady

expansion

and speed

of sound

prevails

Stalker, Mech.,

PI_iXIDtf_

the

the diaphragm

so that during

of the pieces

itself

of

that we analyse.

It is convenient

Fig.

by

the mass of the diaphragm.

NOT

of

for a time after shock

R.J.

"An approximate

Vol. 22, pp 657-670,

FILMED

5

gas

,o, and

upstream u,.

reflection

theory 1965.

This

of the is a good

moves in a as shown in

diaphragm

from

approximation

if the diaphragm

of gun tunnel

a piston)

the

to the

is not leaky.

behaviour".

Joum.

FI.

Thus

the pressure

P/PR

at the diaphragm

= (1

where

y - 1 2

u)2Y/(v aR

u is the velocity

of motion

is given

may

and

(y-lu) 1 --

Pr

2 X

wave

relation

be written

of specific

The

heats.

equation

as

- i}

a r :v

2

this can be solved

and 3' the ratio

therefore

/(v

du dt-

simple

- 1)

of the diaphragm,

for the diaphragm

by the unsteady

(eg.

aar

ref. !) to yield

1 -

1

the co-ordinates

y + 1

u

2

ar

of the diaphragm

1 --Y

- 1

trajectory

(1)

u

--

y

* 1

PR

2

a R

j

1) / (y - i) 2 t

a aR

j

y -1 2

_

y+l

To

yield

quite

Pr

a gain in stagnation

high

stagnation

values

of u/as.

enthalpy

(0.001"), and (2) diaphragm, We now

enthalpy Thus

"

across

with

u/as--

(2)

an unsteady

expansion

2.0 and 3' = 1.4 there of two,

u/a R = 3.

it is necessary is only

Since

reason for choosing the expansion tube mode that tt/aR = 3 or greater. With a diaphragm

to use

a 16% gain

the gain

in

in stagnation

of operation, it seems of mylar 25 # thick

a = 6.0 x 10 .2 kg.m "2, and with a s = 2000 ms t and Ps = 10 MPa, equations (!) indicate that u/aR = 3 at distance x = 12.4 m from the initial position of the at time t = 2.4 x 10 .3 sec. consider

the flow

diaphragm

motion,

diaphragm

may

diaphragm the area

u a R )_(,¢

- for a gain by a factor

enthalpy is the prime reasonable to assume

present

as

u/as

through

the diaphragm

_ 1, so that

be taken

as the

the

if it is leaky.

pressure

undisturbed

and

values

speed

PR and

In the early of a s.

sound, The

stages

of the

upstream

of the

"leakiness"

of the

is represented as a single orifice in the diaphragm, of area b(t) A, where A is of the tube, and b(t) is a factor which generally varies with time, but for the purpose

is assumed

3' = 1.4, the mass flow

to be constant.

rate through

The

the diaphragm

6

flow at the orifice will be

will be sonic

and, with

ria

= 0.578

where The

laR a a b(t)

Pa is the density

A,

in the

pt/

pa

=

the time

Ar

-- 1.73

1

y-1 2

of the expansion

/J, a R )2/(y -

to pass

(1

--u ]z`(v-I) aa)

-

1

If f = 2 m, a R = 2000

tube is p,AL,

and p, is the density

where

L is the length

in the test region,

of

given

by

I)

for this mass

y

region.

the test region,

2

0.1)

undisturbed

mass of gas in the test region

the slug of gas constituting

and

(3)

through

the diaphragm

is

e/a a b(t)

ms 1, U/aR = 3, and we take

the diaphragm

as

10% open

(i.e.

b(t)

=

then At = 177 x 10 's see.

These examples are fairly typical, and other parameters which may

involving values of diaphragm thickness, test slug length be used in practice. They suggest that the behaviour of

the diaphragm as it accelerates and ruptures may have an important influence on the state of the test gas. The turbulence induced by the fragments of diaphragm may affect the quality

of flow

quality of heat not the case. The

fact

produced transfer

in a time

diaphragm

(or

necessary being

records

that an amount

diaphragm

of

which

fragments

to think

processed

as the

by

obtained

gas

is an order

the diaphragm, tubes

to constitute

the

of magnitude

to reach

of a different

an unsteady

through

in expansion

sufficient

thereof)

in terms

steady expansion before follows it. This could

test gas passes

the

model

expansion,

the

test

suggest

test

shorter velocity

for producing test gas

may

although that

flow

than

passes that

the

high

is probably

through for

the

it may

be

test flow.

Instead

of

pass

required

the

that

suggests first

this

the

through

a quasi-

it is accelerated to the test velocity by the action of the gas which change the chemical state of the test gas, though it should be

remembered that the quasi-steady is less than that of the test flow, test flow on its chemical state.

expansion takes place from a stagnation enthalpy and this will tend to reduce the effect of the history

7

which of the

To explore this effect in somev,hatmore detail, a numericalmodel hasbeenconstructed. Due to the natureof thephysicalprocessesinvolved in the bursting of the diaphragmand the subsequentcomplexflow pattern, simple models of the bursting processhave been developedwhich ,,,,illprovidesomeestimateof the flow duringthis process. The

model

for

diaphragm fashion.

the

bursting

of

the

diaphragm

to reduce from full)' covering The mass of the diaphragm

itself

is just

to allow

the

area

of

the

the tube to some minimum area in an exponential remains constant and it is assumed that the

diaphragm remains in one plane throughout the process, i.e. the diaphragm fragments all travel at the same velocib. The time for the burst process to occur and also the reduction in area To

that

occurred

calculate

the

due to the diaphragm

the velocity

diaphragm

must

burst

and acceleration

be found.

This

could

be specified.

of the diaphragm,

was

found

by

the pressure

an iterative

on either

procedure.

The

side

of

average

velocity of the gas on the upstream and downstream sides of the diaphragm were calculated by assuming that sonic flow occurred through the open area of the diaphragm and the remainder of the flow (over the diaphragm itself) moved ,,_ith the velocity of the diaphragm. These two velocities were then averaged taking into account the appropriate areas. From this average velocity, the average pressure on either side of the diaphragm could

be

could

again

The

calculated

flow

solved

using

wave

relations

and

then

the velocity

of the

diaphragm

be estimated. upstream

of the diaphragm

by G. Allen.

velocity

simple

of the

Bursting

was

calculated

of the diaphragm

gas at the diaphragm

using

was

to be the

the wave

included

average

model

in the model

velocity

calculated

developed

and

by forcing by the

the

above

procedure. Two

simple

intermediate through to exist

1. By

models and

acceleration

section

to examine fluids.

the

location

of the interface

Both

assumed

that

the

mass

the diaphragm in any given timestep is known because sonic velocity at the diaphragm. The models then considered two extreme situations,

Model assuming

the expanded be calculated.

between flow

the

passing

is assumed thus:-

1 an isentropic

expansion

back

to the original

area of the tube,

the density

of

mass can be found hence the length which this fluid parcel vdil take up can These lengths were summed sequentially and an estimate of the location of

the fluid interface each mass parcel assumed

were developed

to have

can be found. No correction as it progressed away from

was made for variation of the length the diaphragm, i.e. each mass parcel

constant volume.

8

of is

2.

Model

The

2

isentropic

density

of

expansion

the

diaphragm, mass could

test

was

flow.

Then,

the volume and be calculated.

Test

Conditions

Test

conditions

were

continued

knowing

therefore

chosen

until

the the

the length

to match

a well

density mass

of the

of

the

v,'hich tube

documented

gas

had

which

velocity

Pressure

experimental

(Pa)

Driver

1068.87

33 x 106

1.6667

Intermediate

1019.3

690

1.6667

Acceleration

1019.3

16

1.6667

diaphragm

Pipe

with - Gas

Helium Study

24 metres 0.0762

Secondary

diaphragm

thickness:

Secondary

diaphragm

density:

The

case Perfect lII)

the

up by this

9.93 metres

location:

radius:

PROGRAM

through

taken

2.44 metres

location:

Seconday diaphragm Test section location:

to the

Gamma

(m/s)

Primary

equal

passed was

as the driver and test gases (NASA Tech. Paper 1317 "Experimental of Expansion-Tube Flow Characteristics". J.L. Shinn & C.G. Miller

Sonic

was

metres

38 x 10 .6 metres (Mylar 8.52 x 10 .3 kg/m 3

diaphragm)

OUTPUT

main outputs

of the program

are:

(a) (b) (c)

The path of the shockwave The path of the secondary

reflected diaphragm

The path of the interface for models 1 and 2.

between

(d)

The

from

mach

from

the

line generated primary

from the secondary the intermediate

the intersection

diaphragm

and

the

and

between

reflected

diaphragm acceleration the

section

shockwave

shockwave

from

fluids,

transmitted the

secondary

diaphragm. The simulation and

75%.

One

area

reduction

has been further

nan for burst times of 0.15 ms with simulation

for comparison.

was The

performed

results

for a burst

of these

The final figure is a simulation of the diaphragm not burst but is allowed to move.

9

simulations

acting

area

reductions

time are

as a frictionless

of 10, 25, 50

of 0.30 shown

ms and

25%

in the figures.

piston,

i.e. it does

FigureNotation Burst times Sincethe areareductionis exponential,the burst time usedin the calculations is the time for the areato reach90% of its maximumreduction. Area ratio The areareductionfigure quotedin the atlachedfiguresis the amount by which the area of the diaphragmhas been reducedby the bursting process,(A,,,,u_-AnJ/A,,,,j_. Thus, a 75%reductionindicatesthat the final diaphragmareais 25%of the initial area.

4. The

Results outstanding

acceleration

feature

gas

- test

of the gas

results

interface

is the

as predicted

are apparently unrealistic. Model 1 because expansion to the test conditions, and Model of

gas

which

conditions.

have (This

passed

through

is witnessed

wide

the

by the

disparity

by Model

between 1 and

the

Model

position 2.

of the

Both

models

it does not allow for what is clearly a massive 2 because it does not allow for large anaounts diaphragm

but

velocit2, ." of the

are

not

interface

expanded

predicted

to by

the

this

test

model,

which is far in excess of any reasonable value). It follows that the unsteady expansion after the diaphragm, which has been neglected in both models, is of prime importance. The

motion

of the diaphragm

tends

to slow

down

as the opening

increases.

This

motion

depends on the velocity of the gas at the opening, and is calculated by assuming a simple wave compression from the undisturbed state in the acceleration tube on the downstream side of the diaphragm. Model 2. The overall

picture

It will therefore

which

the results

be unaffected

present

are of a mixed

of the test gas, with the accelerating remains unsteady expansion. It is difficult to analyse required uncertainties diaphragm

for

each

diaphragm

associated before

with

the shock

thickness this, wave

it may

by the choice

steady

be_'een

and

of the diaphragm located such a flow, and a new

and

each

be

arrives.

lO

better

set

of test to think

conditions. of

means

Model

unsteady

1 and

expansion

somewhere in the analysis would be To

avoid

of removing

the the

X

Wave

Diagram

for Diaphram

Acceleration

11

Distance

from

diaphragm

burst

(metres)

0 o ..

I

1

1 0

%

o 0 o o L_ I

%



!'_

o

/

_J U

0 0

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_3 0

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!

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Distance

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(metres) 0 0 o

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Distance

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(metres) ,--4 o o I J





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I 16

I

INFLUENCE

OF

SECONDARY

DIAPHRAGM

ON

FLOW

QUALITY

IN

EXPANSION

G.T.ROBERT$ Lecturer,

Department University

of of

Aeronautics Southampton,

SEPTEMBER

17

1992

and

Astronautics

U.K.

TUBES

ABSTRACT Experiments University which

were

of

the

influence

operated

in

secondary

its with

the

disturbances interface. reducing

momentum and

flow

tube

with

the

of

the

shorter

Pre-deforming reflected

as

only the

is to

gas), the

wave

the

the

flow

the

shock

was

overpressure

disturbances.

18

flow

and

test

the

the

before

shown

side

of

the to

delaying

was

the

exerts but

diaphragm

arrival

a

also

on

shock of gas

beneficial the

a

(compared

driver-test have

and

gases.

reflected the

in

location

conditions

of

TQ

facility

diaphragm

is

with

the

and

inertia

greater

interactions

diaphragm

driver

gas

duration

facility mass,

either

secondary

test the

tube

experiments,

the

the

Engineering,

diaphragm

pressures

both

greater

test

expansion

these

that on

Mechanical

secondary

equal

indicate

general,

attributed

the

argon

not

of In

(i.e.

of

driven

quality

mode

obtained

In

Department

investigated.

influence

duration.

interface

shock

results

strength

by

was

the

free-piston

on

diaphragm)

considerable

in

Queensland

pre-deformation

The

performed

arrival

effect of

the

CONTENTS

PAGE

Title

1

Abstract

2

Contents

3

Nomenclature

4

I.

INTRODUCTION

5

2.

THE

3.

TEST

4.

EXPERIMENTAL

EXPANSION FLOW

4.1TQ

TUBE

QUALITY

- PRINCIPLES IN

EXPANSION

TUBES

tube

facility

4.2

Operating

conditions

4.3

Secondary

diaphragm

Without

RESULTS

7

9 9

variables

I0 11

5. RESULTS 5.1

- TYPICAL

9

DETAILS

expansion

5

OF OPERATION

secondary

diaphragm

11

5.2 Effect

of diaphragm

thickness

13

5.3 Effect

of diaphragm

pre-deformation

15

5.4

of diaphragm

location

16

Effect

6. CONCLUSIONS

16

ACKNOWLEDGEMENTS

17

REFERENCES

18

FIGURES

20

I - 14

19

-

42

NOMENCLATURE

-i a

-

sound

speed,

ms

f

-

frequency,

M

-

Math

p

-

pressure,

kPa

U

-

incident

shock

speed,

-

distance

from

priraary

-

ratio

-

period

between

z

-

steady

run

t

-

total

Hz

number

-i ms

s x

of

specific

diaphragm,

heats shock

period,

and

m

(1.67

for

argon)

test

gas

arrival

(expansion

tube

_s

Subcripts:

Shock

tube

region

(Pitot)

nomenclature:

1

-

initial

test

gas

2

-

post

incident

3

-

post

primary

4

-

initial

5

-

post

reflected

shock

-

post

secondary

unsteady

6

-

post

steady

I0

-

initial

20

-

post

shock unsteady

driver

gas (reflected expansion

expansion

acceleration

incident

expansion

shock

(reflected

shock

tunnel

(expansion shock

tunnel

only) tube

only)

only)

gas in

2O

(expansion tube only) n acc tube (expansion tube

only)

only)

1.

INTRODUCTION

This 1992

report

whilst

describes

the

University

of

Aeronautics

secondary

d/aphragm of

the

head

2.

THE

EXPANSION

TUBE:

An

expansion

tube

of

a

gas

the

reflected shock

low

expansion

reservoir in

the

initially

separates

Figure

I

in

shock

velocity flow

test

is and

use the

obtained

gas of

a

use

sound

typical

whereas,

speed or

a

the

pressure

light

of

in

and

test

gas

free-plston of

tolerated

the

driver under

the

a

from

In

shock

a

gas

above

steady

is

to

that,

a

in

capable

perform/ng

operating shock after

tube,

the

in

rupture

pressure

driver

shock,

tube, primary

of

shock

unsteady which gas.

although

raise

transiently could

Note

region 5

is

Mach

behind

itself number

employing

latter

by

section,

facility.

stagnant

helium)

that

an

acceleration

by

The

test

diaphragm

region

the

followed

the

undergoes

the

a

stagnant in

types

is

between former,

essentially

maximised

levels

the

reflected

both 5

conditions.

21

is

for

high

pressure

ratio.

or

gas

secondary

for

speed

also

d/fference

gas

lower

the

tube

[2]

the

aerothermodynamic

conditions

(thin)

both,

driver

was

that

a modified

from

expansion

(hydrogen

suggested

test

is by

region

sound

topic

initially

shock-heated

the

The

simulated

essential

tube

diagrams

in

region.

the

nozzle

tunnel,

of

gas.

hypervelocity

wave

influence

and

well

quiescent

test

of

driven

the

for

basically

processed

gas

shock

gas

a

expansion

location test

is

If|,

the

work

free-piston

facility

spaceplanes

reasonabl}

contoured

tube

the

enthalpy)

driver-test

an

The

of

R.J.Stalker.

tunnel

suitable

separating

attain

the

reflected

reflected

hence

to

at

shows

the

a

wind

into

further

expansion

centred

high

is

through

expansion

the

gas

conditions,

whereas

that,

and

UNIQ

Prof.

Department

OPERATION.

it

al

the

Engineering,

U.K.

flow.

UNIQ,

or

under

et

gas

flows

pressure

Stalker

tunnel

test

gas

propogated diaphragm

heated

steady

is

at

OF

the

July-September

Mechanical

from

investigate

test

group

of

Southampton, in

to

of

tunnel,

primary

shock

order

vehicles

shock

by

in

test

relatively

described

experiments

period

leave

of

impulse-type

studies

wave

(thick)

an

reentry

the

sabbatical

quality

the

Department

of

Tunnel

is

the

on

PRINCIPLES

of

Like shock

and As

Shock

combustion

a

the

enthalpy

models

conditions. which

the

high

supersonic

(TQ)

on

during

University

number

facility

by

of

visiting (UNI0)

a

tube

testing

undertaken

Astronautics,

perform/ng

producing

was

Queensland

expansion

of

the

author

and

involved

work

a

normally

normally

(and

high d/ctates

increasingly both

the

the

common pressure

In

the

pressure same

expansion ratio

test

for

producing shock

dissociation

in

in

the

reservoir,

stagnant thus

reentry

vehicle

combustion

main

exceedingly magnitude The

reason

for

illustrated flow

is

in

that

this

can

Figure

driver-test

by

gas

operated

in

reflected

the

by

expansion

arrival

at

the

test

Stalker

these

of

the

occur

viscous of

the

test

In

a

even

reason

for

effects:

foot

the

of

this

is by

not

the

the

run

duration

flow,

of

a

typical

supersonic

case)

an

order

wave

period

of from

the

is

through is

to

gas

the

the

limited

unsteady

driver-test

steady

transparent

gas

the

of

diagrams

tunnel

is

is

facilities.

the

the

duration

is

facilities

reflected

interface

off

levels

temperatures

tunnel

tunnel

of

the

the

tube

about

to

tail

over

that

such

is

reservoir

The

acceleration

of

the

unsteady

expansion

the

by

the

expansion

or

interface.

Paull

when

of

optimised

both

the

between

period

of

and

the

driver

shock

and

test

constant

much

causes

with

22

run

than duration

growing

speed

gas

further

interface

earlier the

test

to

but gas)

expansion

also to

due

flow

behind

the

increase

in

the

reflection

be

truncated

_

accelerate. would

been

the

causes

speeds

have

to

from

gas

causes would

in

shocks

layer

shock

often

tests

incident

boundary

uniform

gas

the

in

the it

the

theoretically

observed of

attenuates

length

occur

predicted

times

[5],

driver-test

therefore

run

Mirels

remain

to

times

attenuation

only

the

then

run

the

interface

and

would

and

of

reference

run

showed

expansion

high

a

shock

the

the

the

actual

sufficient

equalize

flow

the

short

the

noted

the

shock

inviscid

the

wave

(and tube

eventually

as

shock

gas

shock

incident

reflected that

often

the

either

of

expansion)

stagnant

however,

of

shown

is

or

where

the

tube,

overestimate

One

(as

the

large.

simultaneously.

Unfortunately, considerably

of

section

have

(shock

so

the flow

who

steady

the

2).

reflected

shock

also

conditions

which

by

poor

expansion

Figure

O(10-4)s,

reflected

if

the

duration

observed

a

by

combustor

run

to

advantage

flight

see

most

mode

expansion

[4]

events

tubes.

or,

drainage

the

and

the

tailored-interface

In

head

be

disturbance

nozzle.

the

In

interface

shock,

of by

easily

the

the

being

in

employ

[3],

stagnated

caused

the

(e.g.

that

offered

i.

of

inside

is

never are

to

on

to

is

Trimpi

primary

experienced

engine

typically

than

limited

which

conditions

by

the

due ratio

superior

is

dependent usual

pressure

However,

not

being

proposed

simulation

disadvantage

less

this

flow

also

restrictions

theoretically

are

is it

to

first

flows,

(scramjet)

small,

if

the

air

the

ramjet

Their

was

a better

or

best

that

(say)

provides

diaphragm,

flows.

is

velocity

Subject

is

is

enthalpy

of

which

it

concept

tunnel

flow

secondary

expansion

high

test

gases.

tube

unsteady

reflected

the

later)

expansion

the

the

acceleration

(described

The that

across

and

quality

tube,

length.

the

of case

early.

in

Nevertheless it is possible and

currently

facilities

establishments

[e.g.

advantages wide

over

rather have

been

viscous

observed effects

Early steady

test

operating [10].

at

condition However,

more

there

depending

on

have

indicated

also

pressure) acoustic

TEST

FLOW

In

work

performed have

increase

as by

of

head

the

case

the

the

Figure various

4

best,

of

inhibit

the is

test

the

conditions

predicted

taking

there

there

was

acceptable

the

that,

In

either a

for

low

any

given

conditions,

addition,

recent

(particularly

transmission

no

single

acceptably

operating

observed

to

was

only

was

indicated

employed.

an

the

arrival

of

the

of

studies

in

pitot

transverse

gas;

steady of

indicated; large

this

is

tail

of

the

from

the

the

the

flow

indicates each

gas

pitot (of

a

the

instead,

the to

23

rise

75

is

is

is

In and

40

@s,

has

operating

pitot

the

arrival

further terndnated

the

reflection In

pitot

either

pressure.

in in

smeared

figures

pitot

signal

or

probably

However,

the

run

in

disturbance.

render

a

increase

arrival

probe).

tO

by

obtained

small

(this

approximately

due

flow

ideal

interface.

signals

arrival

pressure

the

gas

gas

is

an

expansion

further

the case,

terminating

magnitude

above,

unsteady

acceleration

test

the

by

determ/ning

followed

driver-test

indicated

In

rise

soon

pressure

3 shows

initial

the

[13])

the

The

pitot

for

Figure

described

to

of

period.

tube'

conditions.

arrival

run

here,

method

As

from

rate

reported

arrives.

is

RESULTS

diagnostic

tube

expansion

to

TYPICAL

that

main

expansion

gas

(taken

of

TUBES:

including

expansion

response

sufficiently

to

steady

concluded

have

gases

EXPANSION

date,

finite

of

test

related

due

period

number

co,unity

unsteadiness

of

are

increase

steady

number

run

corresponding

the

[4,11]

disturbances

term/nation

before

a

and

test

of

periods

tended

which

offered

theoretical

durations

at

flow

the

larger

are

run

or,

the

acceleration

operating

pressure

a

aerodynamic

tubes

that

for

the

run

be

provided

density

either

to

IN

the

signal low

8,9]

tests

to

during

the

[e.g.

recent

QUALITY

measurements

pressure

has

times

[12,13].

3.

quality

at

their

for

short

test

tested

What the

expansion

which

the

waves

short

realising

within

the

during

driver

during

and

conditions

with

all

ought

the

of

the

account.

conducted

facility,

of

during

of

tunnel.

tubes

even

period

hope

shock

operating

use

developed

the

of

into

tests

in

expansion

range

make

being

reflected

of

narrow

6,7]

the

acceptance

are

to

practice

for

pitot out

by

the

caused

by

the

4a

4b

there

and

respectively) in

a periodic condition

4c

there

is

fluctuation unusable.

no

Paull

and

transverse rupture

gas,

greater filter

whether

that

with

the

The

number,

as

as

in

is

subsequently

the

expansion

of

limitation can

be

on

regular

the

has

rupturing

process)

diaphragm

should

i,,nediately

as

been on

an

instead

initially)

of

t_e

test

as

not (but

of

is

example,

noise

present

as

is

frequency

in

the

converse

interface effect

is

shown

in

show an

to

be

be

flows

has

under

the

focussed

to

a

of

has

caused

if

4

expansion,

appearance

tube

Figure

that,

unsteady

will

The

and

of

were

incident

been

the

observed

major

which

the

to

shock

loss.

In

the and

wave

or

leading

facilities

supporting any valve

the

rupture the

test

increased ideal

gas

will

levels

of

behaviour

diaphragm

necessary

its

case,

else

a

reflected

tube

(and

should

the

commonly

the

expansion

ideal

to

Clearly, but

minimise

in

diaphragm

massless

practice,

of

[14].

shock,

pressure

concern

secondary

quality

the

in

for

the

fast-acting

of

that

pressure

is

difference

disturbance.

arrangement

may

be

employed

a diaphragm. with

the

the

it

reasonable

to

question

Despite

had

cause

it

used

of

quality

a

gas

capable

truncation

this

acts

Stalker

conditions

though

occur

early

of

speed

illustrated

for

expansion

reflected

a mechanical

Additionally,

production.

been

influence

unwanted

will

Alternatively,

flow

and

facilities

the

stagnation

possible it

has

impact

and

diaphragm

is

in

sound

the

runs

effect.

satifactory

which

behave

by

dissociation

across

of

the

Paull

shift

different

range

after

processed

thin

Doppler

gas

dependent.

for

residual

test

low

the

(prior

speeds

filtering

ratio,

gas

sound

whereas

through the

test

a

to

in

the

disturbances,

(by,

frequency

in

feature

developments

the

a

the

present

the

of

due

diaphragm

always

into

interface

for

primary

are

ratio

are

operated.

Another

be

the

the

transmitted

Furthermore,

by

experiments

the the

processed

the

propogated

on

properties

tube)

frequency

disturbances many

flow

hypothesis.

particular

in

the

are

gas,

speed

fluctuations

from

whenever

frequency sound

these

disturbances

depends

are

as

this gas

they

attenuate

cut-off

of

not)

driver

to

well

Inspection

these

interface:

disturbances

unattenuated.

test

the

a tendency

situation

support

gas

that

originating

that

rupture)

in

shown

probably

(or

driver-test

than

have

argue

diaphragm

the

Mach

waves, They

but

secondary

across

[12,13]

acoustic process.

driver to

Stalker

in not

the

expansion been

evidence

run

period the

possible tube

carried

that are role

many caused

of

the

importance flows,

out

prior

24

a

of

the

by

transverse

secondary of

the

systematic to

disturbances

the

work

causing

acoustic

diaphragm

secondary experimental described

in

diaphragm

waves, their on

investigation here.

as

4.

EXPERIMENTAL

4.1

TO

DETAILS

expansion

Figure study.

5

It

is

by air

resides

at

heavy

the

steel

tank the

secondary

location

primary

diaphragm);

secondary The

of

latter

recorder

on

at

40

Operating

operate

to

simplify

of

PCB

on

to

(at the (x

x

-

the

gas) is

A

at

the

full

-

a

Figure

2.111

m

channels

and

34.5

or

25

_Pa. _m

5

is

the of

conducted

the

the with

sidewall

acceleration

in

Data at

to

m).

shock

transducers,

Physical

air

or

downstream

were

and

variation

and

reasonable

in

(P2,t)

shock

gas

aluminium

19.5

offer

3.736

piezo-electric

some

test

driver

the

experiments

along

a

the

range

Shown

pressure

on

the

polyethylene

thought

the

initially

section

of

the _n

pitot

determine

recorded

operating

13

location

locations

were

in

diaphragm

aft

is

high

gas

attached.

as

pressure is

of

gas

the

as

pump

argon

condition.

most

by

acceleration

or

were

driver

test

same

this

_e.g.[6|).

either

both

its

using

Inc.

sample

tubes;

speed

(U). s

All

which

were

pre-

multichannel

rates

of

2MHz,

whilst

kHz.

primary

aim

dlapragm

pre-deforming

to

bursting

the

in

conditions.

secondary

whether

The

study

to

the

the

containing

diffusion

helium

usually

were

used

data

transient

the

various

measured

The

others

in

the

elsewhere

secondary this

necessarily,

use

which

which

section

of

used

accelerated

a

and

massless

taken

also

were

calibrated.

the

the

and

employed

study

ideal

in

at

were

pressures

As

this

diaphragm

(p2)

to

gases.

measurements

pressure

4.2

is

are

forward

in

appears

diaphragms

the

section

rotary

normaly

to

tube

kPa

facility

in

itself

Downstream

diaphragms

to

section,

piston,

not

a

facility

prior

approximation

the

with

tube

kg)

1-10

but

test/acceleration

cellophane;

shock

arrangement

primary

3

Pa.

expansion

driver

order

1-100

section/dump

usual

a

(usually,

order

TO

the

(approx.

of

of

of

free-piston

pressures

of

The

the

a

it,

description

The

schematic

gas

pressures

as

a

facilty.

behind

acceleration

test

a

comprises

compressed pressure

tube

the

a

deformed

state,

these

on

the

the

facility

the

required

of

flow

finite

pressure it

was

flow

quality

diaphragm

in and

experiments

shock

its

has

difference

necessary

to

25

to

explore

and,

in

particular,

any

(rather

analysis.

was

adverse

than Also, (


a 3)

air

to

of

the

if

to

Stalker

[13],

it

speed

was

gas

sound

the

driver-test

disturbances

was greater

gas

originating

in

as

gas

rupture. of

argon

avoid run

driving

argon

causing

vibration

conditions

employed

the

and

test

dissociation

is

given

in

I.

Table

I:

Typical

Run

Conditions

U Pl

reservoir

Primary

2.0

4

2.25

3.7

1

2.75

7.3

pressure:

diaphragm:

Driver

Secondary

the

experiments

mm.

MPa mild

pressure:

diaphragm

Besides

1.85

0.6

reservoir

3

1.65

20

Air

a2/a

s_ 1 (kms )

(kPa)

4.3

unsteady

and

test

filter

choice

to

Paull the

diaphragm

the

preferred

effects).

(i.e.

effective

primary

led

of

where

speed

as

to

analysis

conditions

sound

act

criteria

(the

to at

gas

gas

These

Table

operate

driver

interface

order

according to

the

in

weak.

Finally, necessary

(pl)

75

steel, KPa

burst

pressure

P4

" 19.5

MPa

(argon)

variables

shock

tube

concerned

the

operating

conditions,

secondary

diaphragm.

the

main

Parameters

variables

in

that

varied

were

the

included:

- thickness

(or

- deformation -

The thick

diaphragms

within

102

state,

diaphragms

(prior

tested

cellophane,

undeformed the

location

were

mass)

care

the

were

_uu and was

equalised

to

shock

13 191

taken

the

run) tube

_uu thick

polyethylene,

_m

thick

to

ensure

that

the

pump-down

during

26

mylar.

When the

25 tested pressures

process.

gm

and

in

50

_u

their

either

side

of

5. RESULTS 5.1 Without

Figure

secondary

6

operating

shows

are

of

gas

gas

interface,

can

be

speeds

As also

as

in

Table

both

in

see

is

terminated

any

itself

in

at

without

to

run

rise

obtained

i

obtained

manifests

the

behind time

the Figure

to

any

rise

by

pressure

the

gas

velocity

and

run

period

(T)

the

predicted

mode,

due

to

the

of

rise

in

density

The

except

that

arrival

the

of

pressure.

larger

ratio

one

driver-test

pitot

comparatively

the

nominal diaphragm.

arrival

abrupt

becomes

three

tube

initial

an

the

secondary

expansion

as

the

slightly

unrealistically

of

less

at

wave

is

incident

greater

shock

6

theory

the

is

becondng

gas

the

this

expected,

according

run

those

signals

at

across

It

higher

the

increases.

shown

growth

and

that

in

expect

which

seen

interface

to

course,

acceleration

pitot

listed

similar

not,

shock

typical

conditions

signals would

diaphragm.

the

decreases time

Mirels

[5],

shock.

It

than

that

higher

high

post-shock

theory,

which

with of

be

speeds.

cause

that

shock the

This

the

is

(>

the

viscous

the

pitot

interface

K)

layer

theoretical the

attributed

7000

speed;

boundary

experimentally,

temperatures will

of

turbulent

seen

observed

shock

arrival

assum/ng

can

increasing

discrepancy to

the

predicted

effects

by

to

ideal

be

overestimated. After

the

periodic also

arrival

fluctuations

observed

by

disturbances periodicity

the

steady the

with

occuring

expansion

in 6(b)

in

pressure The the

being pitot

signal

systematic "

4 kPa)

6{a)

or

occuring

at

test-gas

interface

a manifestation

of

(Pl

constant during

the

Figure

higher

has

arrived

the

weaker

during

but

this

disturbance

I

kPa,

for

run

remains

filtering

period exhibits than vs.

some those

28

effect

kHz,

which them

rupture

the

ratio

does

area

not

to seem

the the

these

change

to

be in

runs driver

tests).

fairly

[small) observed

steady,

after

at

although

fluctuations

respectively}.

occurring

by

change

illustrated of

were

process. caused

frequency

scale

to

focusing

respectively, of

large

kHz) by

either

all

kHz

45

frequency

throughout

frequency

27

gas

ratios,

6(a)

{34

frequency

focus

20,

f
a)

discrepancy

in Figure

8 between

the skin

friction and heat transfer trends at position two is a direct result of the lag between skin friction and heat transfer.

(KPQ)

it is evident though that the traces other although only at the first

0.600

generally follow each point does Reynolds

analogy hold. This once again is in agreement with the fact that Reynolds analogy is only purported to be held 0.400_

_hen conditions are laminar. It is interesting that during transition the genera] trend is still followed, although the factor bet_,een the two traces is no longer consistent.

0

0.200

_





|

I

CONCLUSIONS

0.000 0

lO0

2O0

30O

mm from the Learn|

400

500

gdle

It is concluded that where the flow is laminar, measurement of skin friction and h_t tras_sfer ate consistent with

Figure ? Measured plate for condition 3

output. transition,

and predicted

skin

friction

When change occurs, as in this effect becomes noticeable.

the

along

onset

With

shock tunnel applications and approaching needed for expansion tube applications.

the

on_

of

the rise times

ACICNO XVLEDG EM ENTS This

results previously reported by He and Morgan (1989). it C,all be seen thai for these v_ues one would expect transition to occur somewhere between 200 a,'KI 260 mm the leading edge.

analogy.

effective means of measuring shear stress. The gauge has a rise time of about 20 _s, sufficiently short for most

of

Figure 8 shows resuhs for condition 4. It appears that transition is occumng by the second gauge. The Reynolds number at gauge 2 is approximately 1.02x10' amd the unit Reynolds number is 4.gxl0' m':. From

from

Reynolds

transition Reynolds analogy, as expected, breaks do_,n. Also the skin fricuon gauge is shown to be an

work

was supported

by

the Australian

Research

Council under Grant A5852080 and by NASA under Grant NAGW-674. The authors wish to acknowledge the invaluable technical contribution of John Brennan and the

Gauge 2 is positioned at 210 mm

scholarship

from the leading edge.

supporl from Zonta International

Foundation.

R EFERL'_CES

o Heet Trenster (i/ll'/m_ • Skin l_cUon (KP-) 4,

DUNN, M G, (1981) Current Studies at CaJspan Utilizing Short-Duration Flow Techniques. Proceedings of lhe 13th International Sym__lium on Shock Tubes and

3

0

0

Waves. edited by C E Treanor and J G Hall, of New York, Albany, NY, 3240.

O

Z

HE,

Y and MORGAN,

R G, (1989)

State Univ. Transition of

compressible high enthalpy boundary layer flow o_vrer• fiat plale..LQ_h Australasian Fluid Mechanics Conferenfe_ Univ Meib. lIB-2, !1-15.

1

=

0

too

2OO

:

,

3O0

I

4OO

'

KELLY,

'

50O

m.m from Iktd_,, I gdl. F_gure 8 Heat transfer corKlition 4

G M,

SIMMONS,

J M,

and PAULL,

A

(1991) Skin-friction gauge for use in hypervelocily impulse facilities. AIAA Journal, ,;_, 844-845. VAN DRIEST, E R, (1952) Investigation of Laminar Boundary Layer in Compressible Fluids Using the Crocco Method. NACA TN 2597.

and skin friction along plate for

124

I I I_ ,'(Ai llrtJh.451tln

I"luld

Um_rsIQ, oJ Taonw,a, 14-18 December 1992

(. OIHerd/k'd

._f¢CPg2/IlCS

Hobart

4B-4

Ausoaha

ENERGY REDISTRIBUTION

OF NONEQUILIBRIUM IN A SCRAM JET DUCT

N.R. WARD

HYPERVELOCITY

FLOW

and R.J. STALKER

Department of Mechanical Engineering University of Queensland QLD 4072,

AUSTRALIA

ABSTRACT

INTRODUCTION

C%emical]y and vibrationally

frozen shock tunnel test flow

As a means of investigating the gas dynamic effects

is passed through a model scramjet duct with the aim of examining heat release and its effects on the flow in analogy to the heat release resulting from combustion. Experimental investigations arc Ca;Tied OUt using a differential interfcromcter optics system for a range of shock tunnel test conditions. The rtsuhing images arc then compared to a numerical simulation using chemical and vibrational nonequilibrium flow theory fined to the duct shape imposed boundary conditions. NOTATION P T p O

= pressure = temperature = density = flow direction

the energy release instead stored in the dissociation

and in vibrational

rn_es

of of

can be con_crted to

heat energy. This evades the problems of imperfect mixing and flow disruption caused by an injecto¢, and isolates the heat release process from the ignition-process present in combustion.

the scramjet, in much the sarnc way as combustion occur in a prcmixed scrarnjct. See figure 1.

Experimentally it is difficuh to =K:curately measure now conditions using electronic gauges without disturbing the flow. Also, such rncthods involving gauges only provide data at disczete locations, allowing fine detail in the flow to be misse.d. To avoid such problems the

time

rate constants temperature for dissociation temperature for vibration density for dissociation

experirr_mal investigations _st carried study the flow through the scrlmjet.

out using optics to

The optical system used is the Di_crenrial Inzerfcromczcr, or $chlierenInterferomezer.A variationon

¢, = equilibrium vibrational energy t = vibrational relaxation time

the basic system is used making it • double pass system, largely because of space consuaints but also because this

R = gas constant h = cnthalpy

configuration

hq = partial derivative of h with respect to q u = velocity u, = component of velocity normal to shock = frozen speed of sound n ffi refractive index ! = interferogram intensity £ = divergence angle of wollaston

would

In this paper it is aimed to investigate this heat release in a scram jet model over • range of T4 test conditions. For this study a nitrogen test gas is chosen.

Cl.C-a,q=,_= = chemical rale constants = vibrational characteristic characteristic characteristic

molecules

provide Energy

the fn:e stream flow and energy redistribution only recommences _tcr the flow crosses the intake shocks of

e, = vitx-ational energy ¥ = ratio of specific heats 15 = intake wedge angle p = shock angle

C,K= O,_= O. = p= =

test flow to combustion.

The T4 shock tunnel is capable of producing high emhalpy test flow which oontains significant levels of dissociation and vibratiomd excitation. These art frozen in

M = roach number ct = dissociation fraction

t =

of the heat release produced by combustion of h)drogcn in a scrarnjct duct it is intended to simulate such heat release by using chemically and vibrarionally excited shock tunnel

doubles the sensidvity.

This system provides shifts are related to gradient Now field. These experimental

results

shock tunnel arc then compared Chemical

prism

and vibrational

See figure 2.

interferograms in which fringe of refractive index within the obtained

from the T4

=o a numerical simulation.

non-equilibrium

th¢o O, is used to

computationally predict the flow pattern through the scramjet duct for the free stream conditions con'esponding to the experirnents.

= wavelength of laser light w = displacement of wollaston prism from kns focus fz = focal length of main lens x = distance along centreline of model W = width of model

EXPERIMENTAL The

P, = stagnation pressure 1", = stagnation temperature h, = stagnation enthalpy

experimentally non-equilibrium

125

METIIOD

differential

interfcromet¢r

used

to

investigate the chemically and vibrationally flow in the scramjet model as produced by

the T4 shock tunnel is sho_,n schematically in figure :2. A pulse..A ruby laser is used as the light source and all mirrors lure &,round to an accuracy of one tenth of" a wavelength or better. A spatial filter with t 5 pm pinhole is used to clean up the light source and a precision qua,-lz wollaston

C e (r'/° w

p As it does so the tempera'aa-c

prism is used _ith a 4 minute prism angle. The image reu-ieval system consists of CCD camera v.ith 210 mm lens

d'r •

plate

steel is used on all leading

edges

of the model.

precision

cro_n glass _indows,

flat to within

one tenth of

• u,avelength. A pitot probe is fitted above the model check the timing of the laser against [he test flow period. NUM

ERICAL The

computer

program

predicts

flow

shown in figure 3. The flow is symmetrical centre line, so only the bottom half is calculated.

-=_-

-

"" p A, (u 2/a/

('7)

(,_,_'= - _, ae,)

(s)

- !)

v, herc h_ is hen: the The pressure

from conservation

about

the

angle p for the shock of the intake v, edge.

emanating of angle

, y._/I (

/P,_(8-v)

2

I. y- I M_s_(8.p) 2

um p

)

of

- p_

(9)

of momentum.

diffenrntial

equations

are

integrated

using

be parallel

to

the y, all.

This

boundary

condition

requires the superposition of • weak Prandtl-Meyer expansion/compn:ssion on the chemically and vibrafionally adjusting flow. For a deflection of -d_ at the ball for the

f.rorn 8. is

adjusting flow the PrandtI-Meyer penurbafion provides equal and opposite deflection, and gives a penurbation the oqher flow variables according Io:

the in

(!) (10)

The flow valuables are then found behind the shock using the Rankinc Hugoniol equations for pressure, temperature and Mach number ratios across a shock.

aM

As the flo_ passes gong the surface of the wedge it adjusts chemically and vibrationally, as described by Vinccnti and Kruger (1965). according to the following e'qu;tliOns:

_=[C,T"a.CzT'_(]-_)Ip[(I

,)c

'dr-

P-Ea '] Pa

M

(t'_

u_)

"

d_

(Z)

(II)

(12)

and d_`, d_

¢`," -c`, z

(3)

These

perturbations

are communicated

along

Mach |inca

throughout zone 2. They arc added to the adjusting now base values which are calculated for each streamline leading off from abe leading shock. In this way the flow is

_rhere

,Re,, e, - _

a

second order Runge-Kuta n'cthed to obtain the chemically and vibrauonal]y adjusting flow along the surface of the intake wedge.

must

calculated by solving the following equation derived by continuity considerations and the Rankine-Hugoniol equation for density ratio across a shock:

un(8._)

derivative

to q

As u, changes the flow direx6on changes due to the component of u tangential to the shock remaining constant. At the surface of the v, edge however the flow direction

first zone is assumed to be chemically and frozen, and the now to be steady and parallel.

shock edge

Thes_

pas_ia]

h(p.P,ct.e,) _/zh resl_ct changes according to: d.P -

energy e, are all constant,

The leading

by

and for sorr_ q I_ is the partial derivative of hCT.0c,e,) with respect to q and the component of velocity normal to the shock changes accordir,g to:

variables

Consequently pressure P, tem_ratu_ T. density p, flow direction 0, math number M. dissociation fraction cz and

the

(6)

CALCULATIONS

enu 3, to the expansion from the end of the _,edge. allo,_,s the definition o4"three 'zones' of flow, as

vibralional

h'-2_-_'-3=)RT'=_"(!2"

da

experiments has a gap at the cad of the angled intake wedges to allow the shocks to escape ,,_ithout reflection. and the pa.rallel duct ,,,,as designed to be narrow enough to

The vibrationally

to:

to

throughout the scramjet duel from the free stream before the leading edge shocks to the parallel duct behind the shocks after crossing. The test model for the T4

ckny This

according

h is given

when: the cnthalpy

camera to then trigger the laser before clearing the CCD rtgistfrs and storing the image in rnen'or 7 of an IBM 286 compacter. This is then viewed and printed. The model used is 150 mm wide with open sides and is rear mounted in the T4 test secdon. Hardened The intake wedges are 204 mm long and 10 degrees. The shock, tunnel test section is fitted with 200 mrn diameter

changes

- T-i (A,da • k, de ," udu) "r

close mounted connected to a triggered frarncgrabber. Pressure gauges at the end of the shock tube trigger the

gauge

(5)

calculated in zone 2, and the shape of the leading shock is altertd in accordance with the ptnufl)e,d conditions behind it caused by the Prandd-Meyer Fenurbations,

(4)

ee,'T ! 126

The flow using

in zone 3 is calcuhted

the symmea'y

in a similar way,

imposed b_zndary condition of flow

along the duct c¢n1_¢ line heing parallel to t.h¢ duct centre line. Foe each streamline f'mal conditions ahead of the second shock are used to calculate conditions behind the shock which ate then s[a.,'dn i conditionsforthe integration of the chemically and vibratioaally adjusting base flow in zone 3. To these base conditionsthe Prandd-Meyer pcrlurbation$Ire added. From the flow variables thmughom the duct the: refractive index of the flow n and iu gradicn! dn/dx can be calculated using the Gladestone-Dale equation, applied to niuogen molecules and gas with Gladestone-Dale constants as given Merzki_h

in Alpher (1974):

and White

n- ! -

(1958),

as described

pC.g_Ct-a).g_)

by

range of test condiuons chosen there was not recombination in any of them. In order to complete nurncrical simulations for the lest con_Lion$ the free stre_t/n conditions at the entrance to the scram_t were needed 'These were obtained by using l non-equilibrium nozzle flow (NEWZ,F') program to integralc from the shock tube fill pressure, the stagnation pre._sure during the shot and the shock speed in the shock tut_ Numerical simulations obtained using flee svzeam conditions found in this way predicted recombination in zone 2 at least, and an effect which was almost too small to detect when chemical rate constants ts given by Vinccnti

(1990). The

(t3)

interferogram

can be calculated

using the

ecluatJon:

Z The is

imported

_"

numerically into

the

pre_cted sang

experimental interferogram, can be produced, ar,,d this experimental

RESULTS

Iz

differential

which th_se contamination

intcrfcmgram

_,h_ch

holds

the

in this way a pictorial image can then be compared to the

AND DISCUSSION

consequence

and the laser high voltage output trace. The images accorded shov, ed a curvature

of

fringes was observed

produce selection

free stream

vibrational

energy,

the

and

further knowledge

non.equilibrium chemistry and

of T4 conditions

helium contamination will be important of shock tunrgl test condilions for

which in the future

experiments. It is expected that conditions wig attainable in which the nonequilibrium flow through scramjet

the

model

duct

produces heat

release

be the

rather

than

absorption, allowing combustion simulation, although was not the case in the experiments covered here.

this

SUMMARY

AND CONCLUSIONS

Experimental difl'ertntial interfemgrams'of shock tunnel test now througha model scramjet duct have been oblained over a range of high enthalpy test conditions. In

to

vary for different enthalpy and pressun_ conditions, but in all cases the deflection of the fringes was upstream after

all of these cases heat absorption after the intake shocks has been observed. Helium contamination is postulated. Numerical simulations of the flow. when incorporating chemical and vibrational non-equilibrium, have been found

both the fu'_t and SeCOnd shocks. Fringe curvature upon entry to ihe heated outskirts of the boundary layer can also be clearly seen. At the conclusion

a lower

vibration,

edge shock and the second quickly in zones 2 and 3

4. of these

used was as

experiments were carried out helium of the test gas from the driver gas was

See figure 6. h appears that t mort thorough nozzle flow calculation, incorporating

pressures. A differential interferometer image was recorded for each shot together with o'acesof shock speed within the shock tube, stagnation pressure at the entrance to the converging-diverging nozzle, pito_ pressure at the

See figure displacement

energy

fringe shiftis clearlyseen and matches experiment well. As there is an accepted high level of uncertainty in these rate constants comparison against this result is justifiable.

whilst varying the flow pressures and then to choose some other conditions with much lower a to compare. A roach five nozzle was used over this range of enthalpies and

respectively. The

vibrational

Although the fringe displacement at the stm of zone 2 is not suffg'ient to be clearly observed for this calculation. when the calculation is cuffed out using a lower value of the vibrational relaxation time constant C and _ I

image.

fringes after both the leading shock, decaying away quite

fr_ steam

non.equilibrium ctlculafon involving both vibration and chemistry, the computational results were found to be in quite good a_e,,ement with experiment. .See figure 5 for the nmnerical simulation corresponding tO figure 4.

A set of experiments was carried out using the T4 shock tunnel, the results of which are presented here. Chemical pr_esses were initially assumed to dominate the non-equilibrium flow so the test conditions were chosen to maintain a high dissociation fraction a

model

Itwas at this stage

resulting in observations of zero dissociation of nitrogen test gas. in cont;,adic_ion to the pun: test gas case calculated by the NENZF pmgra.m. When this was used in the numerical simulation, coupled with the more complete

=

electronics

were used

predictedby the method of Phinney (1964). Vibrational non.equilibriumeffects_¢re found to bc highly significant to the flow. Skinner (1992) found that at the high cnthalpies at

From the gradient dn./dx, a knowledge of the T4 test section and model gcomc_ies and specifications of the &ffemnfial interfcrometer opticssTstem the fringe intensity | of ihe resulting

and Kruger (1965)

that the previously describ_ ueatment of vibrational nonequilibrium was included, using more re.cent values of the vibrational rate constants as given in Sharma and Park

of the experiments the images

were analysed and the deflection of the wollaston prism calibrated. Consequently it was confirmed that a d¢flectioe upstream signifies a raising of refractive index

to be in good agn:ement with experimenL Future experiments will involve a complete non-equilibrium nozzle flow calculation to select test condilmns which

gradient from zero and thus increasing density. This is verified by examination of the fringe shift entering the boundary layer. This ¢ormslx:mds to energy obwrp6on rather than heat release. The implicatioe of this is that despiz the wide

produce

127

heat

release.

ORIGINAL

PAGE

!$

OFPOOR9UAU

REFERENCES ALPHER,

R A and WHITE,

D R (1958)

Optical

Refractivity of High Temperature Gases. L Effects Resulting from Dissociation of Diatomi¢ Ga._s. The Physics of Ruids, Volume 2 Number.2., 153-16t. MERZKIRCH, W (19"14) Flow Academic Press, New York u_d London. PHINNEY. R (1964) Nondimensional Flows V lu

with

Vibrational

2 Number SHARMA,

simulation

and

Relaxation.

2, 240-244. S P and PARK, diagnostic

noncquilibriurn flows. _Hcat Volume 4 Numtx:r 2, 129.142. SKINNER, K (1992) Department

of

Mechanical

Visualisador_. Solutions

ATAA

C (19