# Parallel BVI Noise Investigation Using Compressible Vorticity

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```					Parallel BVI Noise Investigation
Using Compressible Vorticity
Confinement Method

Helicopter
Study Weekend.
The Burn, April 2003

Romuald Morvant
Computational Fluid Dynamics Lab
University of Glasgow               Sponsored by WHL
Summary

1-Introduction
2-Vorticity Confinement Method
3-Optimisation of the BVI calculations
4-Acoustical results for the near field
5-Conclusions
6- Further work
Noise Sources of the Helicopter
Vorticity Confinement Method

Developed by Steinhoff and coworkers
Has been successfully applied
to a large range of CFD applications:
Helicopter flowfield, Delta wing

Dissipation kills the vorticity

Momentum
Energy
Expressions of the Confinement Terms
Efficiency of the CVCM
Vortex Convection
Simulation

After 15 cycles
Vortex-Airfoil Interaction
 Reproduce existing test cases

Subsonic test case: S. Lee & D. Bershader
(1994)
-Vortex generated in a shock tube
- Surface pressure measurements

NACA0012
a=0.0

x/c=0.02, 0.05, 0.10
Optimisation of the BVI Simulation
 Optimised calculations for Inviscid & Viscous
Vortex parameter

M=0.5, G=-0.283, R=0.018
Confinement parameter ()
Grid sensitivity

Time step sensitivity (Dt=0.01, Dt=0.001)
Optimisation of the BVI Run
Vortex Location
x/c=0.02
Inviscid calculations on
a grid of 485k pts
Optimisation of the BVI Run
Vortex Location
x/c=0.02
Inviscid calculations on
a grid of 485k pts
Optimisation of the BVI run
Spatial Dependency
x/c=0.02
Inviscid calculations
Optimisation for Inviscid Runs
 Vortex location & confinement parameter
 Confinement parameter relatively easy to find
 Similar results at 1.5 & 4.5 chords ahead
 Grid sensitivity
 Same magnitude for the Cp at x/c=0.02
 Vortex core-size may slightly increase
 Time step sensitivity
 Dt=0.01 enables to capture the main interaction
 Dt=0.001 if secondary structures are to be
captured
Viscous (Re=1e+6) & Inviscid
x/c=0.02
Calculations
on coarse grids
Acoustic Pressure
for the Subsonic Case

 Grid of ~220k points & Time step=0.01
Sound Pressure Level

Sound Pressure Level

Sound Pressure Level

Optimisation of the Viscous Calculations
Turbulence Models
x/c=0.02
Viscous calculations on
a grid of 220k pts
Optimisation of the Viscous Calculations
Turbulence Models
x/c=0.02
Viscous calculations on
a grid of 220k pts
Influence of the Angles of Attack
Viscous calculations on
a grid of 220k pts

x/c=0.02
k-w turbulence model
Influence of the Angles of Attack
Viscous calculations on
a grid of 220k pts

x/c=0.05
k-w turbulence model
Acoustical Pressure
for the Transonic Case
Schematic of the BVI run
M=0.8, G=-0.20, R=0.05
Vortex-Shock Interaction
Conclusions
 Vorticity Confinement Method
 Vortex preserved & cheap calculations
 Results obtained for inviscid & viscous simulations
 Importance of the vortex location
 So far, the k-w and 1-equation models seem
the most appropriate for Cp prediction
 Importance of the confinement parameter
 The VCM has to be switched off around the airfoil
 Calculation on a uniform grid
Further Work
- Modification of the turbulence models
- Parametric study on airfoil thickness, M & Re
numbers, incidence, turbulence.

Vortex-Airfoil Interaction Simulation
 Determination of the Acoustic Near-Field
 Determination of the Kirchhoff surface using
processing signal methods
 Determination of the Acoustic Far-Field
-Directivity study
-Study of possible ways for reducing the noise

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