Master Diploma Thesis Presentation

CFD SIMULATION OF A VORTEX CONTROLLED DIFFUSER FOR A JET ENGINE BURNER

Analiza CFD Sterowanego Wirowo Kontrolera dyfuzora komory Spalania Silnika odrzutowego

By:Emeka Chijioke

Supervisor:Prof. Andrzej Teodorczyk

POLITECHNIKA WARZAWSKAWYDZIAŁ

MECHANICZNY ENERGETYKI I LOTNICTWA

DEPARTMENT OF AIRCRAFT ENGINES

OUTLINE

Motivation

Objectives

Numerical Methodology

Reynolds Average Navier Stokes Equation (RANS) Turbulence model ( RNG k-) Transport equation

Numerical setup

Computational domain, Grid and boundary conditions

Numerical results and comparison

Conclusion

MOTIVATION

The demand to design more efficient flow separation control system.

Improving the efficiencies of gas turbine engines and compressors.

Influence of the suction slot on the separation behavior of boundary layers and pressure recovery.

OBJECTIVES

To generate a grid and perform a numerical computation of a 2D vortex controlled diffuser (VCD).

To observe the effects of the vortex chamber geometry on diffuser performance.

  To obtain and analyse the flow properties.

Compare the results obtained.

Conservation Law

in outMinm outm

outin mmdtdM

outin mm

0dtdM

MassMomentumEnergy

Reynolds Average Navier Stokes Equation (RANS)

NUMERICAL METHODOLOGY

Navier-Stokes Equation I

Mass ConservationContinuity Equation

Compressible

Navier-Stokes Equation II

Momentum ConservationMomentum Equation

k

kij

j

i

i

jji x

UxU

xU

32

I : Local change with time

II : Momentum convection

III: Surface force

IV: Mass force

V: Molecular-dependent momentum exchange (diffusion)

Viscous stress tensor

Navier-Stokes Equation IV

Energy ConservationEnergy Equation

is the heat flux vector

is the total energy per unit mass, and

is the total enthalpy per unit mass

Model Equations. The transport equations are solved for the turbulent kinetic energy (k), and disipation rate () (improves the accuracy for rapidly strained flows)

Turbulence model: RNG k- model

The transport equations are as follows:

Gk - generation of turbulence kinetic energy due to the mean velocity gradients.

Gb - generation of turbulence kinetic energy due to buoyancy.

YM - the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate.

Computational domain

Vortex-controlled diffuser (VCD) computational domain

COMPUTATIONAL SETUP

Computational domain of the VCD without the bleed geometry (step expansion)

Computational domain

COMPUTATIONAL SETUP

Grid and boundary conditions for the VCD

No-slip wall: u=0, v=0 axi-symmetry at the Inlet: velocity is equal to 60 m/s. at the outlet1: pressure outlet is equal to zero pascals. at outlet2 (bleed duct): 0%, 1%, 1.2% and 2% of the operating pressure. operating pressure is equal to 1 MPa.

Velocity Inlet

Pressure outlet 1

Pressure outlet2

Boundary layer mesh enlarged

No-slip walls

Five Boundary conditions

Axisymmetric

No-slip walls

COMPUTATIONAL SETUP

Grid and boundary conditions for the VCD wthout bleed geometry

No-slip wall: u=0, v=0 axi-symmetry at the Inlet: velocity is equal to 60 m/s. at the outlet: pressure outlet is equal to zero pascals. operating pressure is equal to 1 MPa.

Four boundary conditions

COMPUTATIONAL SETUP

GRID SENSITIVITY STUDIES

Summary of the grid independence study

Grid No. Mesh Element Type No. of Cells

No. of Face

No. of Nodes

1. Coarse mesh

(No boundary layer)Quad. 1985 4149 2165

2. Fine mesh Quad. 3064 6333 3270

3. Finer mesh Quad. 4782 9846 5065

Chosen grid

B

Screening test results

RESULTS AND COMPARISON

Model Axial gap, X[m]

Radial gap, Y[m]

Inlet Mach

number, M

Static pressure

rise [Pa]

Reattachment length, LR

[m]

Bleed rate [%]

123

0.00450.010*0.015

0.00250.1330.133*0.133

-1283-1035*-750

0.38750.3840

*0.36501.0

456

0.00450.0100.015

0.00450.1330.1330.133

-1204-1002-772

0.40000.38500.3740

1.0

789

0.00450.0100.015

0.00850.1330.1330.133

-1049-853-850

0.40000.38630.3862

1.0

*- Final geometry chosen

B

Variation of static pressure rise for various values of axial gap X for constant radial gap Y- 0.0025 m

Variation of static pressure rise for various values of radial gap Y for constant axial gap X - 0.015 m

Variation of static pressure along the centre line of the VCD

RESULTS OBTAINED WITH THE FINAL VORTEX CHAMBER GEOMETRY

CONTOURS OF STATIC PRESSURE FOR VARIOUS BLEED RATES

Static pressure contours (Pascal), for the VCD without bleed geometry

Static pressure contours (Pascal), 0% Bleed

Static pressure contours (Pascal), 1% Bleed Static pressure contours (Pascal), 2% Bleed

STREAMLINE PLOTS OF VELOCITY FOR VARIOUS BLEED RATES

Streamline plots of velocity magnitude (m/s), for the VCD without bleed geometry

Streamline plots of velocity magnitude (m/s), 1% Bleed

Streamline plots of velocity magnitude (m/s), 1.2% Bleed Streamline plots of velocity magnitude (m/s), 2% Bleed

Radial profiles of velocity at the inlet plane at various bleed rates, (flow fully turbulent)

Radial profiles of velocity at mid-plane at various bleed rates

Radial profiles of velocity at the exit-plane at various bleed rates

Contours of Velocity Magnitude (m/s), for VCD without bleed geometry

CONTOURS OF VELOCITY MAGNITUDE FOR VARIOUS BLEED RATES

Contours of Velocity Magnitude (m/s), 1% Bleed

Contours of Velocity Magnitude (m/s), 1.2% Bleed Contours of Velocity Magnitude (m/s), 2% Bleed

CONTOURS OF STATIC TEMPERATURE

Contours of Static Temperature (k), for VCD without bleed geometry

Contours of Static Temperature (k), 1% bleed

Contours of Static Temperature (k), 1.2% bleed Contours of Static Temperature (k), 2% bleed

Conclusion

The VCD performed better than the VCD withouth the bleed geometry.

The air bleed performed well in reducing the velocity thereby improving the static pressure rise.

Velocity magnitude at the exit of the VCD without bleed geometry is 47.5 m/s, while velocity magnitude for VCD with the bleed geometry reduced from 60 m/s to 41 m/s for 1% bleed and 10.5 m/s for 2% bleed.

Best position of the vortex fence is at axial gap, X= 0.015 m and at radial gap Y=0.0025 m.

Minimum bleed rate is 2%.

Thank you for your attention !

emekachijioke9@yahoo.com