Flow and Noise Predictions for the Tandem Cylinders · PDF fileFlow and Noise Predictions for the Tandem Cylinders BANC-II Workshop ... –For both mean and unsteady surface data and

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Flow and Noise Predictions for the Tandem Cylinders

BANC-II Workshop

Category 2

June 7th 2012

© Exa Corporation Confidential 2

Numerical simulation

Simulations performed with Lattice Boltzmann based

solver PowerFLOW 4.2 – D3Q19 LBM

Cubical Lattices (Voxels)

Surface elements (Surfels)

– Explicit compressible solver – Fully transient – turbulence approach

Modified RNG k-ε model

Swirl model – Anisotropic “large” eddies resolved – Statistically universal eddies modeled

Extended wall model – Taking pressure gradient effect into account


Simulation Overview

Two simulations will be presented – periodic spanwise boundary conditions (Brès et al. 2010)

Referred to as LBMperiodic

Overall, good comparison with experiment

However, enhanced coherent shedding observed

– setup matching QFF experimental geometry, including the jet

nozzle and spanwise side plates (Brès et al, 2011, 2012)

Referred to as LBMQFF

To investigate installation effects

– For both cases, span of 16D matching experiment

16 D

L = 3.7 D


Match QFF geometry and setup – Open jet, with end plate and collector – Unchanged flow parameters

(M=0.128, Re = 166 000)

setup for LBMQFF simulation

QFF experiment

Side plates

Open jet

collector


Boundary conditions: – Outlet: constant Pressure P0 = 10 000 Pa

– Large acoustic buffer zone to damp spurious reflections – Surface roughness of 0.05 mm

on upstream cylinder only

to duplicate boundary layer trip used

in the experiment

Steady flow at nozzle exit – However, velocity U0 = 42 m/s, instead of 44 m/s like in

periodic simulation and experiment – Apply Strouhal scaling St=fD/U0 for frequency, and St2U0

6 for

pressure fluctuations

Numerical details

Time-averaged streamwise

velocity at the nozzle exit


Mesh: – structured Cartesian mesh (cubic cells) generated automatically – fixed refinement ratio of 2 between adjacent levels – Finest resolution: 0.446 mm (128 pts/D)

Performances – Total number of cells: 210 millions – Time step size = 7.348 e-07 s – Number of time steps = 680437 (0.5 s) – Simulation cost for 0.5s of data ≈ 32 000 CPUH

~5 days on 256Cores

Grid and parameters

nozzle Side plates


Lift and drag time history

Upstream cylinder Downstream cylinder

Mean CD = 0.59 Mean CD = 0.29

Mean CD = 0.56 Mean CD = 0.30

LBMperiodic

LBMQFF

Exp CD ≈ 0.59-0.63 Exp CD ≈ 0.29-0.31

Drag

Lift

Experiment


LBMperiodic

LBMQFF

Experiment (BART) Experiment (QFF)

mean surface pressure coefficient†


Good agreement, no difference between the 2 simulations

†spanwise averaged, mean computed from last 0.3s of data


unsteady surface pressure coefficient†


• RMS levels overestimated for setup with periodic BC • better agreement with LBMQFF simulation

LBMperiodic

LBMQFF


†spanwise averaged, RMS computed from last 0.3s of data


spanwise correlation of surface pressure


Better agreement with experiments with spanwise side plates included in the simulation

θ = 135 ° θ = 135 °

LBMperiodic

LBMQFF



unsteady surface pressure spectra†


θ = 135 ° θ = 45 ° Overall, accurate prediction of the

peaks and dB levels

†FFT (10 Hz Bandwidth), Hanning window (50% overlap), Signal length of 0.3 s

LBMperiodic

LBMQFF



16D

instantaneous density field

LBMperiodic

LBMQFF

Wide range of small-scale features and

significant spanwise variation visible in the computational

domain

Measurements in cross-section plane y=0

16D


instantaneous vorticity field

LBMperiodic

LBMQFF

Experimental PIV (BART)

Numerical results qualitatively similar to BART PIV in terms of large-scale roll up, shear layer

break up and small-scale structures

Measurements in mid-section plane z=0


mean streamwise velocity†

Gap between cylinders (y/D=0) After downstream cylinder (y/D=0)

Quantity challenging to accurately measure, but reasonable overall

comparison †spanwise averaged, mean computed from last 0.3s of data

LBMperiodic

LBMQFF

PIV (BART) “zoomed” PIV (BART)


2D Turbulent kinetic energy (1)

LBMQFF

x/D = 1.5

y/D = 0

LBMperiodic

LBMQFF

Experiment (BART)

Experiment (BART)


Experiment (BART)

2D Turbulent kinetic energy (2)

x/D = 4.45

Overall, similar trends between experiment and

simulations for 2D TKE data (both levels

and shapes)

Comparison improved with

LBMQFF simulation

y/D = 0

LBMperiodic

LBMQFF

Experiment (BART)

LBMQFF


• Good agreement on peak frequencies and overall levels • But peak levels overestimated in LBMperiodic

• Results significantly improved with LBMQFF

radiated noise spectra (1)

Far-field calculation – Using FW-H solver† (wind-tunnel formulation) – Input: solid surface measurement (cylinders ONLY)

†G. A. Brès, F. Pérot, and D. Freed, “A Ffowcs Williams-Hawkings Solver for Lattice-Boltzmann Based Computational Aeroacoustics,” AIAA-2010-3711

Flow

Mic A (-8.3D, 27.8D)

Mic C (26.5, 27.8D)

Mic B (9.1D, 32.5D)

Mic B Mic C Mic A

LBMperiodic + FW-H LBMQFF + FW-H Experiment (QFF)


noise contribution from side plates

Include side plates as input to FW-H calculation

LBMQFF + FW-H (Cylinders ONLY) LBMQFF + FW-H (Cylinders & side plates) Experiment (QFF)

Mic B

Directivity

• Similar predictions, but higher levels: +2-3 dB in the broadband +1-2 dB at the peaks

• Improved agreement with experiment


Insight on side plates contribution Compute SPL of surface pressure (1/3 oct. band)

– On both cylinders and side plates (i.e., FW-H input surfaces)

Band 88 - 111Hz Band 146 - 176Hz (main shedding frequency = 170 Hz)

• For all bands, imprint of shear layers. could potential cause increase in broadband levels

• dipole pattern visible on side plates. could potentially cause increase in peak levels


radiated noise spectra (2)

FW-H calculation with permeable surface as input

LBMQFF + FW-H (box1) LBMQFF + FW-H (box2) LBMQFF + FW-H (box3) Experiment (QFF)

Mic B

Directivity

Side plates

nozzle • Best agreement with large surface box3 enclosing side plates • Except for “hump” in directivity


Compute SPL of surface pressure (1/3 oct. band) – On permeable surface “box3”

Insight on permeable surface contribution

Band 55- 70Hz Band 146 - 176Hz (main shedding frequency = 170 Hz)

• “hump” in OASPL directivity at downstream locations likely caused by low frequency contribution (50-100 Hz) due to shedding off end of side plates


Conclusions Large simulation possible at reasonable computation cost

– About 5 days on 256 processors, for 16D span including side-plates and nozzle

Good overall agreement between the two simulations and

experiments – For both mean and unsteady surface data and flow field – For radiated noise spectra and directivity

Significant improvement with the presence of the spanwise

side plates in LBMQFF simulation – For rms and spanwise correlation of surface pressure – For amplitude of tonal peaks in the far-field noise

Installation effects investigated with side plates included

in FW-H calculations – +1 to +2 dB at tonal peak levels – +2 to +3 dB in broadband levels

Improved comparison with experiments


Backup slides


Aeroacoustic benchmark

Tandem cylinders configuration – Simple enough for detail experimental and

numerical investigations – Complex enough to retain the key flow

features and interactions present in more realistic landing gears.

Extensive experimental measurements – Basic Aerodynamic Research Tunnel (BART) – Quiet Flow Facility (QFF)

BART Jenkins et al. (2005, 2006)

Neuhart et al. (2009)

QFF Hutcheson and Brooks (2006)


Simulation and experiments

Simulations performed using the lattice Boltzmann based solver PowerFLOW 4.2 – Explicit solver – DES like turbulence model

Modified RNG k-ε model Swirl model

– Fully transient solver

Comparison with experiment – Basic Aerodynamic Research Tunnel (BART) – Quiet Flow Facility (QFF)

BART QFF


Lattice Boltzmann Method

The Boltzmann equation :

The discrete Boltzmann equation can be written

This is an exact form if both and are nodes on a lattice (mesh). It corresponds to:

– Using a set of constant discrete velocities, a fixed lattice (mesh) can be chosen

to allow CFL = 1 everywhere at all times

Macroscopic quantities can be recovered by a simple summation

( , ) ( , ) , 1, ,i i i if x v t t t f x t t i b

ix v t x

| | / 1iCFL v t x

( , , ) ( , , )t

f x v t v f x v t

bi i txftx ),(),(

( , ) ( , )b

i i iu x t v f x t


Unsteady Surface Pressure Spectra†

Theta = 0 deg


θ = 0 ° θ = 0 °

†Simulation: FFT (10 Hz Bandwidth), Hanning window (50% overlap), Signal length of 0.3 s; spanwise averaged Experiment: FFT (3.125 Hz Bandwidth)

Experiment (BART) Experiment (QFF) PF (periodic BC) PF (QFF setup)



Theta = 45 deg



θ = 45 ° θ = 45 ° Experiment (BART) Experiment (QFF) PF (periodic BC) PF (QFF setup)



Theta = 90 deg






Theta = 135 deg






Theta = 180 deg





Mean Streamwise Velocity†

PF (periodic BC)

†Mean computed from last 0.3s of data

PF (QFF setup)

Contours between u/U0 = -0.3 and 1

-Similar results overall - Influence of endplates in spanwise direction noticeable after downstream cylinder


Results: solid FW-H measurement OASPL directivity at 26D - details

FW-H total

Upstream cylinder

Downstream cylinder

End plates

Experiment

Flow

Details of OASPL contributions: - Noise mainly from downstream cylinder -Strong directivity from upstream cylinder - nearly constant levels for end plates

OASPL computed for f > 50 Hz, for 0.3s of data


Influence of FW-H measurement box 1 vs box 2 vs box 3

Mic A

Mic B

Mic C

-No significant differences -Box 3 slightly higher


Results: permeable FW-H measurement OASPL directivity at 26D - details

FW-H box 1

FW-H box 2

FW-H box 3

Experiment

Flow

Details of OASPL contributions: - similar results for box 1 and 2 (inside plates), under predicted by 2-3 dB - better agreement with experiment for box 3 (enclosing end plates) - “hump” at downstream locations due to low frequency component (between 50 and 100 Hz), maybe shedding from end plates ?

OASPL computed for f > 50 Hz, for 0.3s of data


Porous Box 3

Solid

Results: solid vs permeable OASPL directivity at 26D

FW-H solid

FW-H permeable box

3

Experiment

Flow

- Good agreement between solid and permeable formulations, except for downstream locations (low frequency contribution)

OASPL computed for f > 50 Hz: -“hump” for box 3 -No “hump” for solid, nor box 1, 2


Influence of sampling frequency box 3: 21 vs 10 vs 5 kHz sampling

Mic A

Mic B

Mic C 5.3 kHz

sampling

10.5 kHz

sampling

21 kHz sampling

Experiment

-visible drop in dB starting around 900 Hz if sampling at 5.3 kHz -visible drop in dB starting around 1.5 kHz if sampling at 10.5 kHz cutoff at 6 points per period


Influence of sampling frequency surface: 21 vs 10 vs 5 kHz sampling

Mic A

Mic B

Mic C 5.3 kHz

sampling

10.5 kHz

sampling

21 kHz sampling

Experiment

-visible drop in dB starting around 900 Hz if sampling at 5.3 kHz -visible drop in dB starting around 1.5 kHz if sampling at 10.5 kHz cutoff at 6 points per period


Influence of FW-H formulation wind-tunnel vs moving source

Mic A

Mic B

Mic C

No difference between wind-tunnel and moving source (with u = 0 m/s), because M = 0.128 very small

WRONG CORRECTION !!! +0.404 dB instead of +0.808 dB

Documents

Flow and Noise Predictions for the Tandem Cylinders · PDF fileFlow and Noise Predictions for the Tandem Cylinders BANC-II Workshop ... –For both mean and unsteady surface data and