STAR-CCM+ Anders Tenstam Volvo Technology AB Anders Tenstam, Volvo - - PowerPoint PPT Presentation

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Automotive Fan Noise Modelling using STAR-CCM+

Anders Tenstam Volvo Technology AB

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Volvo Technology – a business unit within the Volvo Group

AB Volvo

Business Areas Business Units Volvo 3P Volvo Powertrain Volvo Parts Volvo Information Technology Volvo Technology Volvo Logistics

Renault Trucks Mack Trucks Volvo Trucks Nissan Diesel Buses Volvo Penta Volvo Aero Financial Services Construction Equipment

• Volvo Technology is the

center for innovation, research and development in the Volvo Group

• The customer base is

limited, focusing on the Volvo Group, Volvo Cars, selected suppliers and public bodies

• Secures hard & soft product

& process innovation for superior end customer solutions

• Established 1969
• Locations: Gothenburg,

Lyon, Greensboro, Chesapeake, Hagerstown, Los Angeles

• ~500 employees

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Vehicle CFD Team - Main Focus : Support Volvo Group with Methods Development & Resources in:

• Aerodynamics
• UTM (Heat management & Fan operation)
• Aeroacoustics
• Climate / HVAC
• Internal flows
• Fuel Cell Technology
• In-cylinder model development

Trucks Construction Equipment Buses

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Understanding Fan Noise – the Motive:

• Fan noise is one of the main contributors to noise pollution from

heavy-duty vehicles.

• The overall noise level from a heavy-duty vehicle is an entity

controlled by legislation.

• Given a certain discharge flow, the link between hydraulic efficiency

for a fan and emitted noise is quite strong. Hence a quiet fan has also normally low losses.

• A large truck fan at high load can consume 30-35kW of power from

the crank shaft, a substantial portion of the mechanical power from the engine.

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

The Project - Goal:

• To predict and understand noise sources using CFD simulations.
• To investigate the propagation of noise sources to far-field; directivity.
• Increase the in-house understanding of fan noise, i.e. what is important

in low noise emission fan design? The Project - Facts:

• The project was sponsored by the Volvo Group Key Technology

Comittee and performed during 2008-2009

• The numerical part of the project was performed by staff from Volvo

Technology and Volvo Aero Corporation.

• Masurements were made by the NVH lab at Volvo 3P.

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

The Project - Scope:

• To predict the major noise sources in two fan installations
• f an Articulated hauler:
• Low-range frequencies from LES
• High-range broad-band signatures from URANS
• To predict propagated noise using acoustics analogies
• Propose ways to further reduce noise in the installations

A: In-house developed AH fan at VCE

• B. Conventional heavy-duty fan

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

The Project – Scope contd.

• The computational time frame for each geometry must not exceed 1
• week. This way, the developed method may allow for fan noise

calculations to be fit into product development chain.

• Perform LES simulations of each fan, and extract noise sources and

frequency spectrum up to threshold given by maximum model size.

• Propagate sources to far-field by a FWH (Ffowcs-Williams Hawkins)

integration routine.

• Perform URANS simulations to allow for additional broad-band

character noise prediction

• Analyse and Compare with measured data

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

The Computational Model

Model facts:

Region #Cells Fan Region 800 000 Outer Region 1 900 000 Radiator 100 000 TOTAL: 2 800 000

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Results – URANS Simulation (Broadband Sources):

Volume Noise Sources (Proudman): Logarithmised values (Isosurface corresponding to 100 dB):

[W/m3] Where AP = Acoustic power [W/m3] ε = constant ρ0 = density [kg/m3] a0 = speed of sound [m/s] U = Turbulent velocity scale L = Turbulent length scale This equation is implemented in STAR-CCM+ 4.06.011 Similar regions are depicted by adopting the Curle Expression for surface sources

5 5 3

a U L U AP

c

 

 

        

ref

P AP dB AP log 10

Derived from k, ε

Suction side (upstream) Pressure side (downstream)

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Results – Broadband Sources contd.:

• Broadband sources are strong in the tip region, especially for fan B. This

leads to blade-to-blade interaction, which is a strong noise contributor.

• For the less noisy fan (A), additional sources exist at mid-radius due to partial

separation (improvement potential).

• Tip leakage leads also to performance degradation (improvement potential).

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Results – LES Simulation (Narrow Band Sources):

• Simulations run for 2-3 revolutions for quasi-stationary behaviour
• Pressure data is collected for 2 revolutions
• For each surface cell, a discrete Fourier Transform is performed, and

data is mapped back to the model surface directly or summed up by frequency bands (3rd octave or octave) using ProAm+shell scripts

Maximum theoretically resolved frequency (Nyqvist Frequency): fmax = 1/(2*t) where t = sampling time (s) Maximum attainable frequency is however limited by the grid spacing (Mesh cut-

• ff Frequency). Derived from URANS simulations as a relation between turbulent

velocity scales and length scales Minimum resolved frequency: (and also the frequency resolution to be captured by the Discrete Fourier Transform) is the inverse of the interval length T fmin = f =1/(N*t) = 1 / T where N = number of samples

Near blade surface: max. 2 kHz Blade wakes: max. 1 kHz

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Results – LES Simulation (Narrow Band Sources): RMS values of pressure series (logarithmised):

• Distinctly lower sources

are present for the less noisy fan (A)

• Sources are mostly

concentrated to area near tips, these are linked to the tip vortex.

• Stator (shroud)

interaction levels are stronger for fan B.

• Frequency

decomposition reveals strongest contributions around BPF.

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Results – LES Simulation (Narrow Band Sources) – Moved Fan: RMS values of pressure series (logarithmised):

When the A type fan is moved axially, a substantial increase in surface pressure fluctuations is encountered!

Fan A in Nominal position Fan A moved partially out of shroud

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Fan A Fan A moved Fan B Fan A Fan A moved Fan B Fan A Fan A moved Fan B

Directivity (power spectrum), BPF marked with arrow

Beside fan: High levels at frequencies above BPF

Fan A Fan A moved Fan B

On axis (+): Fan A: BPF dominates. Fan B: 0.5*BPF dominates

• n pressure

side (fan/shroud interaction)! Downstream Upstream

Results – LES Simulation (Propagation - FWH):

Time series in a listener location (on axis) Fan B Fan A Fan A, moved

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Results – Summation over whole observer sphere, A-weighted, third

• ctave band filtered. Experimental results from echo chamber:

Fan A moved (PWL) Fan B (PWL) Fan A (PWL) Fan A Measured (SPL) Fan B Measured (SPL)

+20 +10

• 10
• 20
• 30
• 40
• 50

Conclusions:

• BPF is well resolved for all fans
• Broadband character above BPF is less well represented, the contribution
• ver ~800-1000 Hz is exaggerated (probably caused by the tip vortex and

blade-to-blade interaction. Overall, the results are promising. Remarks:

• Different results definitions required for simulations (PWL) and

experiments (SPL).

• Fan A position was not specified to 100% in experiments.
• Due to Sliding mesh interpolation routine, simulations were slow. No

significant speedup detected above 4 CPU:s on single quadcore machine. A significant speedup should be expected if this is resolved or the model can then be made finer (problem could be parallelized more).

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Summary

• LES Calculated noise level (PWL) fan A compared to fan B: -5dB
• URANS Calculated noise level (PWL) fan A compared to fan B: -6 dB
• Measured noise level (PWL) fan A compared to fan B: ~ -10dB

Results are very direction sensitive. If the noise level is evaluated on the rotation axis, the simulation difference between the two fans is 6-9dB.

Vehicle CFD Team at VTEC

Anders Tenstam, Volvo Technology AB

Vehicle CFD

STAR European Conference March 22-23 2010

Thank you for listening!

Noisy fans…