[AS_Aero]

Hi All

As everyone says CFX is good for turbo-machinery related stuffs.

I am interested to know if any of you have done some engine cooling fan simulation using CFX and if Yes how would you recommend CFX over other softwares ?

Secondly would like to know if CFX is capable of doing the Aeroacoustics part of the cooling fan ? I am kind of new to this cooling fan field and I am not aware about the same. It would be great if someone could give me some insight about the same.

Also does CFX can give information about the noise sources as well as the noise radiation from the fan to the far field ? Both Broadband and Tonal noise ?

[ghorrocks]

Yes, CFX is good for turbo machinery. But it is not so good at doing very complex geometries such as the flow over an engine block. The cut cell, overset and other mesh technologies in Fluent would assist in modelling the engine block.

CFX can do noise sources but no CFD code is suitable for acoustic modelling to the far field. CFX can do the noise generation, but you will need to couple it to an acoustics code like SYSNOISE for far field modelling. This is the same for all CFD codes, you need a linear acoustics model for the far field model and a non-linear CFD model for the noise source.

[AS_Aero]

Dear Glenn

Well I at present I am not considering the engine block, I just want to simulate the Fan alone. Maybe with Stator Casing behind the fan. And its funny that Ansys tech support says Aeroacoustics can be done with CFX. My main concern is to do some CFD simulation and Identify the noise sources in the Fan and then identify the noise level at far field of the fan. Lets say 1m away from the fan at different operating condition. Both broadband and tonal noise. And compare it with the experimental measurements.

From what you are saying : CFX can do the Noise Generation which means by using CFX we can identify the noise sources but not the propagation of the noise to far field ?
And for identifying the noise sources we need to use some acoustic models right ? Which is available in the CFX already ?

[ghorrocks]

My post said you can do aeroacoustic modelling, it is just that modelling out to the far field will require coupling to an acoustics code. If your observer is only 1m away then that is not really far field.

CFX solves the full 3D Navier Stokes equations. This can model just about any fluid flow situation including acoustics. So if you have unlimited computing power you can model all acoustics situations. But this requires a super fine mesh out to a long way out and is impractical for most people. So you couple to an acoustics code so you just solve the far simpler, linear acoustics equations once the full Navier Stokes solver has got the noise source generation.

CFX has no built in acoustics models. Acoustics are just pressure waves and CFX will just give you the pressure waves. You will then need to turn that into sound pressure levels, dipole sources and all the other acoustics features.

[AS_Aero]

Dear Glenn

Thanks a lot for your great explanation. But the one you mentioned SYSNOISE is not available now. Do you know any other software which is not that expensive to couple it with CFX ? I tried Actran which is from MSC Software and they are really expensive for solving Aeroacoustics problem, so does PowerFlow from Exa, which uses LBM.

[ghorrocks]

For something which couples easily to ANSYS software like CFX I would ask ANSYS. I have not done acoustics modelling for a long time so my contacts are all out of date.

Also note PowerFlow is a lattice boltzmann flow solver. It is not something I would recommend for acoustics modelling, but it is an alternative for the noise generation at the rotor model.

[AS_Aero]

Dear Glenn

Thanks a lot. Recently I had a chat with the Ansys guys and they said we can do acoustics by using the Structural Packet of Ansys. FEM solver solves the Wave equation. We can couple CFX to Ansys mechanical and do either vibro acoustics or aeroacoustics. This really surprised me and my doubt is, what they are discussing about acoustics is same as aeroacoustics what I want to do. Although they say its possible to propagate the noise sources to the far field using the Ansys Mechanical.

[ghorrocks]

I did see in the ANSYS APDL manual they had some acoustics elements. Feel free to look into them and see if they work for you. It would be a good solution if it has all the features you need.