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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%.
