ROMAGNOSI English presentation

8/7/2019 ROMAGNOSI English presentation

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SAPIENZA UNIVERSITY OF ROME

SCHOOL OF AEROSPACE ENGINEERING

MASTERS DEGREE IN ASTRONAUTICAL ENGINEERING

LES OF COMBUSTION IN SUPERSONIC REGIME

FOR SCRJ APPLICATIONS

SUPERVISOR STUDENT

Prof. Claudio Bruno Luigi Romagnosi

ASSISTANT SUPERVISOR

Ph.D Antonella Ingenito

Ph.D Donato Cecere

Academic Year 2009/2010


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Goals of thesis

2

The analysis of mechanisms of vorticity and turbolent production

in the field with the ultimate goal to optimize the mixing and

anchor the supersonic flame

Validation of results using measurments from the HyShot project

[Rif. Report on the Hyshot Scramjet Experiments in the T4

Shock Tunnel, M. Frost, A. Paull, H. Alesi]

X-51 A Waverider New concept space launcher


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3

Introduction

- Ramjet Scramjet

- How SCRJ model engine works

- HyShot scramjet program

Numerical approach

-Mathematical model and simulation set-up

- Closure models (SGS / EDC)

- Numerical scheme (Weno35)

Simulation results

- Description of the fluid dynamic field

- Study of the vorticity production and diffusion terms

- Combustion analysis

Conclusions and future developments

Contents


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SCRAMJET = Supersonic Combustion RAMJET

RAMJETis the evolution of the turbojet which, based on the idea of

Ren Lorin (1913), have no rotating parts. The absence of

compressor and turbine allows higher temperature in the combustion

chamber.

RAMJET SCRAMJET

RAMJET limits: C.C works in the subsonic conditions sharp

slowdown of the flow in the air intake high

temperature in the C.C limit on the maximumflight speed (M 5)

Solution: keep a supersonic flow in the combustion chamber (SCRJ)

Why studying SCRAMJET?


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How a SCRJ model engine works

5

Future: advantages:

High flight speed (M=6-12) No need for carrying oxidizer on board:

SCRJ uses air (for new concept launcher)

Drawbacks:

Must be accelerated up to M=6 Low residence time in c.c.(10 -3 10 -4 s) mixing is critical

Air intake

Combustion

chamber

Thrust

plate


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HyShot scramjet program

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HyShot is a research project developed at the University of Queensland

Centre for Hypersonics (UQ) in order to demonstrate the feasibility of

supersonic combustion via flight tests (jointly with US and UK)

1st stage (Terrier) tburnout = 6.4 s

V = 4000 km/h

h = 3.7 km

2nd stage (Orion) tburnout = 27 s

V = 8300 km/h

h = 56 km

Test Fuel: H2tinjection = 6 s

h = 35 - 23 km

M = 7.6 7.4

Trajectory data:

Apogee: h= 314 km

Mission profile:


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Simulation of HyShot combustion chamber

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= 0.426 Air Hydrogen

Pressure [Pa] 82110 307340

Mach 2.79 1

Density [kg/m3] 0.2358 0.3020

Temperature [K] 1229 250

Sound speed [m/s] 682.9 1204.4

Flow speed [m/s] 1905.291 1204.4

Simulation Data from UQ ground testing in the T4 SWT (h = 28 km ; AOA = 0):

305 mm x 100 mm 300 mm x 75 mm x 9.8 mm 200 mm x 75 mm


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Mathematical model and simulation set-up

8

Solver: Explicit and compressible

Method: Finite difference (placed variables)

Numerical scheme:Runge-Kutta 3rd order(time integration)

Hybrid: Finite differences 4th order-WENO35 (spatial integration)

SGS Model: Fractal

Riemann problem solver: HLLC/HLLE

Boundary conditions: NSCBC (Navier-Stokes Characteristic

Boundary Condition)

Kinetic scheme: 9 involved species and 37 chemical reactions

Reactive N-S:

Species transport

equations:

Eqn of state:

No.nod

es=

5

010

6

(448

x12

8x878)


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SGS (SubGrid Scale) closure models

9

Fractal nature of turbulence:

Hp: large Re

inertial range below

(eddy viscosity) with

Combustion model (EDC):

fine structures

V* = *V


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WENO35 numerical scheme

WENO (Weighted Essentially Non-Oscillatory) is the evolution of a scheme introduced for the

first time in 1987, developed by Harten, Osher, Engquist and Chakravarthy. WENO35 has third

order accuracy where the variables are discontinuous, and fifth order where smooth.

(candidate stencils for the reconstruction)

Case:r = 3 (5 cells) Accuracy: 2r-1 (smooth)

r (not smooth)Lagrange polynomials:

with

If the solution is

smooth in all Sk:

with


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WENO35 validation

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PROGRESSIVE WAVE

REGRESSIVE WAVE


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Simu

lat i

on re

sults

(1/2)

H2 expands and

(vorticity generated

by baroclinic effect)

12

900 m/s

Mach disk

Barrel shock


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Simulation results (2/2)

M=2.40.6

T=250310 K


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Study of (vorticity)

Vorticity transport equation:


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Baroclinic term (1/3)

It is the only true source term of vorticity (as is

not a function of )


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Bar

oclin

icterm(2/ 3

)

16


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Bar

oclin

icterm(3/ 3

)

17

1

2

3


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Vortex Stretching (1/2)

The vortex stretching promotes the turbulence energy cascade through the

combined effect of stretching and tilting:

Rigid rotation does

not contribute to

vortex stretching

For example, to simplify matters:Incompressible fluid div(u)=0


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Vortex

Stre tc

hing( 2/

2)

UZ

= 200 - 1800

m/s

19


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Compressibility term (1/2)

Compressibility plays a dual role:

I. Reduces molecular mean free path shortens chemical time

II. Increases molecular collisions lower species interdiffusion(important for diffusion flames)

Mean free path:

Reaction rate [kg/m3s]:

k = ATb e

EA

/RT

(Arrheniuss kinetic theory)

Kelvins Theorem:

A = cost

L

L

(Incompressible fluid)

(Compressible fluid)


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Compre

ssib

ilit

yter m

(2/2)

21

div(u)>0

div(u)


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Viscous terms (1/3)Viscous terms are f(), diffuse vorticity and create small-scale vortices close

to the wall.

Dimensionaless form of vorticity equation:

with

NB: IfRe 1 then VISCOUS FORCES INERTIAL FORCES

Re 1 temperature rise

u flow slows down close to the wall

chemical reactionswall friction

Linked to thesecond derivativesof the vorticity. Itproduces vorticity

in opposition to the

vortex stretching

Lighter particles aresubjected to greaterdecelerations due to

viscous stress. Itproduces vorticity in

opposition to the

baroclinic term

Vortices directed in a generaldirection are redirected along

a definite direction whensubjected to viscous gradients

in the other two directions


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Viscous

ter

ms(2/3)

23


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Viscous

ter

ms(3/3)

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COMPETITION BETWEEN

MASTER-SLAVE VORTICES

VS

Boundary layer separation at z = 53 mm

caused by p=8000 Pa in ~1 mm

V i i d Mi i (1/3)


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Vorticity and Mixing (1/3)

Vt = 1000 m/s

d = 2 mm

= 10-5 Pas

= 0.3 kg/m3

Re = 60000

= 500000 rad/s

K = LRe-3/4 0.5 m

t = TRe-1/2 50 ns tm

DIFFUSION

FLAME???

NOTE: NO KOLMOGOROV BUT FM (COMPRESSIBILITY)

= 105 106 Hz


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Vortic

ityan dM

ixin

g(2/3)

26

H l (T 250 k)


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Vortic

ityan dM

ixin

g(3/3)

= 80000 300000 rounds per second

H2 core very cool (T=250 k)

heating and consumption

from the outside

Competition between master slave vortices

instability of flame surface in favor of mixing

Redistribution of H2 along the

walls (tilting of spanwise

vorticity) increase in heat

transfer surface air/wall-H2

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M i h i l i


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YH2 0.2 %

YOH 1.5 %

YH2O 10 %

Main chemical species

Si l ti lid ti


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Simulation: validationno. 16 pressure transducers

spaced 13 mm apart. The

first is located 9 cm

downstream of thecombustor chamber

entrance.

THRUSTPLATE

AIR INTAKE

COMBUSTION

CHAMBER

C l i


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Conclusions

The LES simulation of the HyShot II combustion chamber highlights some interesting

aspects:

this simulation predicts complete combustion in supersonic regime (flame anchors

already 2 cm upstream of the injectors)

crossflow injection allows rapid fuel-oxidant mixing; the baroclinic effect caused

by the expansion of the H2 jet produces high energy vortical structures

the baroclinic contribution is of the same order of magnitude of the vortex

stretching and compressibility terms (1010 rad/s2).

the hydrogen low density contributes to the production of vorticity (B is inverselyproportional to the square of )

combustion efficiency is very high (only 0.2% of the total mass at the

combustion chamber exit is H2)

F t d l t


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How much fuel injected affects vorticity production (for example,

kerosene: RP-1 800 kg/m

3

vs H2 0.09 kg/m

3

)

What is the thrust contribution by fuel momentum (for example,

vary the angle and the injection pressure)

How much the injector geometry affects the mixing (fluid jet

destabilization, injecting from slits)

What is the increase of entropy in different configurations (search

for the optimum set-up that gives minimum S). This simulation shows a

S of about 37/mol K through the combustion chamber

Future developments

arget: Looking for the right balance between mixing and thrust produced

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