Computational Aero-Acoustics - Siemens

Copyright Free Field Technologies

Computational Aero-Acoustics

STAR-CCM+ / ACTRAN for Computational Aero-Acoustics

CD-adapco STAR AMERICAS Conference, June 28, 2011

Authors: Yves Detandt, Marie Cabrol, Romain Leneveu, Diego D’Udekem, FFT

Fred Mendonca, CD-adapco

Presenter: David Burd, FFTNA

2 Copyright Free Field Technologies

Contents

Introduction - Hybrid Acoustic Approach

Tandem Cylinder Benchmark

Tandem Cylinders Problem Statement

CFD input

ACTRAN simulation

Results

Automotive HVAC Noise Example

Fan Noise Example

Conclusions


Introduction - Hybrid Acoustic Approach

1. Unsteady flow computation (STAR-CCM+)

2. Acoustic noise sources computation and propagation (ACTRAN)


Tandem cylinder benchmark

The First Workshop on Benchmark problems for Airframe Noise

Computations (BANC-I) was held in Stockholm, Sweden, June 10-11,

2010. The workshop was organized by the Discussion Group on

Benchmark Experiments and Computations for Airframe Noise

(BECAN),1 which is jointly sponsored by the Fluid Dynamics and

Aeroacoustics Technical Committees of AIAA.

The BANC Tandem Cylinders model is available here:

https://info.aiaa.org/tac/ASG/FDTC/DG/BECAN_files_/Workshop_June_

2010_Final_Problem_Statements

https://info.aiaa.org/tac/ASG/FDTC/DG/BECAN_files_/Workshop_June_2010_Final_Problem_Statements

https://info.aiaa.org/tac/ASG/FDTC/DG/BECAN_files_/Workshop_June_2010_Final_Problem_Statements


Problem Statement

Flow Speed:

Mach 0.128

U0 = 44 m/s 158 km/h

Re = 1.66 x 105

Experimental Configuration:

12D span for flow measurements (BART)

16D span for acoustic measurements (QFF)

Experimental configuration (ref 2.)

Tandem Cylinders - Geometry (ref 1.)

Schematic of microphone locations (ref 2.)


CFD Input

CFD1 (Provided by Fred Mendonca, CD-adapco, on STAR-CCM+ v5.06.007)

Grid: 6.7 million cells

Dimensions of the computational domain:

• 33.7D x 30D x 12D

Time step: 10-5 s

Time interval for spectral analysis:

• 0.46503 s to 0.56503 s (0.1 s)

Data size: 1.2 TB (mesh+solution)

Boundary conditions :

• Free Stream: M = 0.128

• No-slip at cylinder walls

• Periodic boundary conditions in the spanwise direction

Aeroacoustic results limited to 2800 Hz


CFD Input

CFD2: reduced CFD domain + coarser mesh (STAR-CCM+ v5.06.007)

Grid: 1.07 million cells

Dimensions of the computational domain: 24D x 11D x 12D

Time step: 3.10-5 s

Time interval for spectral analysis:

• 0.27228 s to 0.37227 s (0.1 s)

Data size: 180 GB (mesh + solution)

Boundary conditions:

• Free Stream: M = 0.128

• No-slip at cylinder walls

• Periodic boundary conditions in the spanwise direction

Aeroacoustic results limited to 1000 Hz


ACTRAN Simulations

Two different meshes/simulations were used:

CAA 1

Domain extension: 43D x 15D x 8D

159,898 dofs

Performance: 5 min/freq

Mesh valid up to 1000 Hz

CAA 2

Domain extension: 43D x 15D x 8D

1,684,270 dofs

Performance: 1.75 h/freq

Mesh valid up to 2800 Hz


ACTRAN Simulations

Experimental coherence

Correlations reach 0 for Span/D > 8D

Simulations

Consider spans of up to 8D from CFD results

Use the symmetry of the problem

Reproduced from

AIAA-2007-3450


Results – Microphone A

Microphone A

CFL3D results (AIAA-2007-3450)

60.10e6 CFD cells

CFD 1: 7.10e6 CFD cells

CFD 2: 10e6 CFD cells


Results – Microphone B

Microphone B


60.10e6 CFD cells




Results – Microphone C

Microphone C


60.10e6 CFD cells




Results – Varying Data Sample Rates

Investigations on data sample rates (on CFD 1 data)

1e-5 s is the CFD time step for CFD 1

Conclusions:

Results are not sensitive to data sample rate

Data storage could be reduced by a factor of 10

This investigation is required on each test case


Results

Correlation between different time series

Investigate the acoustic signals due to different time series in a single

ACTRAN run:

Maximum and minimum for each frequency defines the envelope

Average of 6 acoustic signals

Similar to experimental processing

t t+0.02

t+0.01 t+0.03

t+0.04

t+0.05

t+0.06

t+0.07

t+0.08

t+0.09

t+0.10

CFD results

Loadcase 1

Loadcase 2

Loadcase 3

Loadcase 4

Loadcase 5

Loadcase 6


Results – Microphone A


Results – Microphone B


Results – Microphone C



German Automotive consortium proposed a benchmark to simulate the

noise generated in a simplified HVAC configuration

Experimental setup

(reproduced from AIAA-2008-2902)

ACTRAN model (AIAA-2009-3352)



Experiment:

Full anechoic wind tunnel

17 microphone array rotated

through 17 positions

Simulation:

STAR-CD: 2.5 million cells, 0.1s flow solution

ACTRAN:

Envelope of the experimental data

Differences in peak amplitudes are related to

approximations in damping modeling


Fan Noise Example

Simplified radial compressor (12 blades)

Speed: 2000 rpm

Blade Pass Frequency: 400Hz

ACTRAN Results:

Tonal components (BPF and harmonics) due to interaction of blade unsteady load

with diffuser

Broadband level due to downstream turbulence

BPF

1st harmonic


Tandem Cylinder Study Conclusions

Several CFD parameters were compared:

Data sampling frequency

Maximum frequency estimates from turbulent kinetic energy

Different time series

Several acoustic configurations (hard wall and duct modes variables had a

significant effect on results)

STAR-CCM+ / ACTRAN software combination provides good

correlation with experimental results.

Advantages:

No need to refine CFD grid to propagate acoustics up to an FWH surface

because Actran does not use FWH for this type of analysis.

Several acoustic investigations can be performed using the same CFD data.

Acoustic boundary conditions (free field, duct modes, etc.) were imposed

separately from CFD boundary conditions.

Actran includes convenient acoustic post processing.

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