Sound sources of radial compressors – experimental and numerical studies

Lars Enghardt1, Jakob Hurst2, Till Raitor1 and Wolfgang Neise

1German Aerospace Center (DLR), Engine Acoustics2Berlin University of Technology

Outline

• Introduction• Experimental study (on the suction side)• Spectral characteristics of radial compressor noise• Acoustic mode analysis for source mechanism identification• Numerical study on the pressure side• Conclusions

Folie 3

Introduction

Aerodynamic noise of centrifugal compressors used forturbo-charging Diesel engines on board of ships or in power stations has become serious problem for manufacturers

Goals of the experimental study:

Knowledge of dominating aerodynamic sourcemechanisms

Reduction of blade tone noise of radial compressorsthrough design measures

Experimental study of radial compressor noise to assess thespectral characteristics and explore the aeroacousticgeneration mechanisms of the rotational noise

Numerical study of radial compressor noiseon the pressure side

DLR.de • Chart 4

Experimental study

DLR Radial Compressor Test Bed

Folie 6

Experimental set-up

Measurement stations

Impeller SRV2 and Vaned Diffuser

Impeller SRV2D = 156/224 mm, Z = 13/26

Outlet diffuser with profiled vanes ZD = 23

Spectral Sound Characteristics; SRV2; Vaneless Diffuser

Circumferentially averaged sound pressure spectra in immediate inlet duct

nred

80

100

120

140

160

180

0 10 20 30 40 50Frequenz [kHz]

Scha

lldru

ckpe

gel [

dB]

BPF2 BPF

3 BPF4 BPF

Azimuthally Averaged Sound Pressure Spectra

SRV2, vaneless diffuserSRV2, vaned diffuser

nred = 36,000/min, immediate inlet duct

Frequency [kHz]

Soun

d pr

essu

re le

vel

[dB]

Tip clearance noise

Folie 10

nred = 50,000/min; immediate inlet duct

Azimuthal Mode Analysis of Spectral Components

80

100

120

140

160

180

0 10 20 30 40 50Frequenz [kHz]

Scha

lldru

ckpe

gel [

dB]

BPF

2 BPF

3 BPF

4 BPF

SRV2, vaneless diffuser SRV2, vaned diffuser

Soun

d pr

essu

re le

vel [

dB]

Frequency [kHz]

Folie 11

BPF = 10,900 Hz

SRV2, vaneless diffuserOperating point(design point):nred = 50,000/minMred = 2.56 kg/sΠtot = 5.44

Azimuthal Mode Spectra in Immediate Inlet DuctSRV2, Vaneless Diffuser

BPF = 10,900 Hz 2BPF = 21,800 Hz

VsZhm SR ⋅−⋅=&

:(1962) Sofrin&Tyler

Folie 12

130

140

150

160

170

30 35 40 45 50red. Drehzahl [1000/min]

Ges

amts

chal

ldru

ckpe

gel [

dB]

21 3

0,8 0,9 1,0 1,1 1,2abs. Umfangsmachzahl (Laufradeintritt)

unbeschaufelter Diffusorbeschaufelter DiffusorVaneless diffuser Vaned diffuser

Dominated by tip clearance noise

Dominated by blade tones

Dominated by blade tones

and buzz-saw

noise

Overall SPL in Inlet Duct, SRV2

Impeller tip Mach number at intake

nred [1000/min]

Ove

rall

soun

d pr

essu

re le

vel [

dB]

DLR.de • Chart 13

Numerical study

- 14 -

» Numerical Analysis1. Sound generation: 360° CFD-simulation of impeller, vanless diffuser and volute

2. Radial mode analysis (RMA) at volute outlet extraction of sound pressure field

3. Sound propagation: CAA-simulation of discharge pipe

• background flow: RANS-simulation

• inlet boundary condition: Imposed sound pressure field from RMA

2. Transition zone

3. CAA

1. CFD

© 2017 – Acoustic emission into discharge pipes - 30.03.2017

- 15 -

» 360° CFD-simulation

– TRACE: CFD-code developed for turbomachinery by DLR

– Fine grid resolution to avoid numerical dissipation/dispersion: 170 Mio. cells

– HPC-Cluster Aachen/Jülich (JARA): 600 cores - Intel Xeon X5675 (2TB RAM)

Test section

NozzleDamping section

VoluteDiffuser

Impeller

Inlet-nozzle

© 2017 – Acoustic emission into discharge pipes - 30.03.2017

- 16 -

» 360° CFD-simulation– BPF1 pressure fluctuations in Pa

– high noise level at volute outlet

– inhomogeneous field at volute outlet

© 2017 – Acoustic emission into discharge pipes - 30.03.2017

volute outlet

- 17 -

» Radial Mode Analysis (RMA)

» Extraction of acoustic mode field from URANS simulation via RMA at testsection.

© 2017 – Acoustic emission into discharge pipes - 30.03.2017

RMA

Up- and downstream propagating modes 1. BPF.

𝑝𝑝𝜔𝜔′

URANS

Folie 18

Conclusions

Experimental study 4 radial compressor configurations tested on DLR-test bed:

1) SRV2 with vaneless/vaned diffuser2) SRV4 with vaneless/vaned diffuser (no results presented here)

Dominant noise generation mechanisms identified by way of spectral and mode analyses

Data base established for further evaluation

Numerical study 1 radial compressor configuration numerically modelled Dominant compressor tones (BPF1 & BPF2) on the pressure

side simulated and analysed by means of radial mode decomposition

Ongoing project to develop an accurate in-duct measurmentsystem with low sensor count for industrial needs

Folie 19

Acknowledgements

Financial support of the project by the

German Ministry of Economics and Labourvia the German Federation of Industrial Research Associations, AiF

and the Research Association for Combustion Engines, FVV

is gratefully acknowledged

Furthermore, the numerical study is financially supported by the