Do you know any SOFTWARE to be able to solve aeroacustic problem in Automotive field like this: how I investigate pressure fluctuations generated by unsteady hydrodynamic flow structures on the vehicle surface that are a source of wind-generated noise? How can evaluate noise and buffeting problems for the "spider" car. I have found on the web a paper with PowerFlow about this problem. Can you send me further information?

Yours sincerely

Gabriele Vèlenich

1) Aeroacoustic is one of the remaining big problems in CFD. But some steps are done. 2) STAR-CD offers a tool which claims to be able to do such analyses. But as far as I know this tool is "only" a post processing tool which generates pressure fluctuations based on the calculated turbulence field. May be this is sufficient to solve engineering problems like the reduction of buffeting. 3) Powerflow also claims to be able to solve aeroacoustic problems. This is due to the fact that powerflow in general only performs time dependent simulations with a very small time step. For the buffeting problem that is may be enough because you can expect frequencies lower then 100 Hz. But even for this frequency you should use a time step lower then 1/600 sec 4) In any case the results strongly depend on the ability of the code to solve for the turbulence in the flow field and this is as you know also one of the big problems in CFD 5) to sum up: with lots of experience in CFD connected with experimentation you may be able to judge wether one geometry is better then another due to noise generation. But you should not expect to get exact results of frequencies or noise levels

In general, there are 2 big issues in computational aeroacoustics, one is the acurate temporal and spatial resolution of the source terms - you need a lot of mesh and you need to run with very small timesteps.

The other is the propagation of those sources to the far field where they are heard by the 'observer'. This can be done either directly (i.e mesh the far field => even more mesh!) or analyticaly using something like Ffowcs-Williams/Hawkins version of Lighthill's acoustic analogy (lots of net references for this).

In most problems the noise energy is a very small percentage of the total (say 1-2%) so if your flow solution contains a couple of % error your noise prediction will be completely wrong.

Our software RADIOSS-CFD is mostly used for aeroacoustic numerical simulations. RADIOSS-CFD ios a FE code that solves the NS equations (LES turbulence) fully coupled with the structure in the time domain (explicit time integrator). We provide boundaries with prescribed acoustic impedance as well. So far, the code has been used successfully for problems like exhausts, intakes, centrifugal and axial fans, side mirrors and generally speaking components. Full car simulations require *lots* of CPU ressources. You can check our website for examples and published papers: www.mcube.fr

Dimitri Nicolopoulos

Dear Gabriele,

PAM-FLOW from ESI Group is a finite element based explicit solver that is used extensively for aeroacoustics simulations within the automotive industry. PAM-FLOW can handle both low frequency and high frequency phenomena.

Proven automotive applications include sunroof and side window buffeting, wind rush noise due to side mirrors, A-pillar, wipers, roof-racks etc., and internal components such as intake manifolds, engine cooling fans and HVAC systems.

We provide an integrated auto-mesher that facilitates boundary layer meshing, even for ultra-complex geometries. CPU requirements are addressed by highly scalable parallel solvers.

Please visit our website (www.esi-group.com) or contact me for additional details.

Best Regards Kosala Wickramasinghe ESI North America kwickr@esidetroit.com www.esi-group.com

Hi,

The Fluent6.0 version would be able to do aero-acoustic modeling. This can be done through use of udf built by FLuent.

Lighthill-Curle analogy is used for noise computation in which it was not necessary to have grid upto the observers point.

The code has been verified for simulating noise due to flow over a

1. Flat plate 2. 2D cylinder.

For both the cases the results were in GOOD aggrement with the experimental one. Both the sound generated and dominant shedding frequency was claculated in close aggrement(St. Number was 0.191 for Fluent & 0.186 for Experiment).

However, this was done using LES for modeling flow. The noise prediction would be directly depending upon the prediction of pressure values.

The overall code is very easy to use and had been demonstrated to customers like GM.

Bipin