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Registered: ‎02-08-2012

Setting up Compressible Flow

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02-08-2012 12:20 PM

Hi, I am relatively new using CFD, and am having difficulties setting up a forced external compressible flow analysis, as in a windtunnel. As such, I was looking for some advice/help on what my boundary conditions, solve settings, etc. should be. I am modeling air flowing over a sensor, which contains a heating coil.

 

My known conditions:

Inlet velocity: 330 knots (Mach .54)

Inlet Temperature: -23C

Heater Wattage: 193 W

Pressure : 3.55 psi (Pressure of static air at the temperature and altitude the wind tunnel is at. I am not sure if this is a nessesary value, or if I can use a 0 gage pressure at the inlet and an unknown at the outlet, which seems to result in a large velocity gradient at the entrance of the "wind tunnel.")

 

I know that I need a velocity boundary condition at the inlet (330 knots), a total temperature at the inlet (-23C), a pressure at the inlet (?), a pressure/unkown at the outlet (?), and a Total Heat Generation on the coil (193W).

 

Questions:

1. What pressure conditions should I apply?

2. Should I used a fixed or variable setting for the air environment? 

3. Should I input material enviroment settings? If so, I assume -23C and 3.55psi?

4. When solving, what should be on and off? I currently have Flow (compressible at -23C) and Heat Transfer (forced) on. 

5. Are there anything other settings that should be applied/altered? 

 

Thanks.

Product Support
662 Posts
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Registered: ‎08-24-2011

Re: Setting up Compressible Flow

02-08-2012 01:09 PM in reply to: mojo2907

Just wanted to know first if you have reviewed the external compressible flow guidelines?  There is a section in there for compressible wind tunnel models.

 

https://www.cfdesign.com/OnlineHelp/2011/Guidelines/Compressible-External.htm

 

-Royce



Royce Abel
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Registered: ‎02-08-2012

Re: Setting up Compressible Flow

02-08-2012 01:32 PM in reply to: Royce_adsk

I have, and after running the simulation to what I think is correct, the velocity profile looks relatively correct, although this being my first simulation with this kind of sensor, I am reluctant to call anything correct until I know things are set up right. However, I am getting rediculous temperature numbers, as in the flow at the inlet is on the levels of 100,000 degrees farenheit, and the heater is something like 10,000F so Im pretty sure I am doing something wrong. The heater shouldnt be this hot, and even if it were, it shouldn't affect the inlet air to become hotter than the heater itself. Could this be a material issue?

Product Support
662 Posts
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Registered: ‎08-24-2011

Re: Setting up Compressible Flow

02-08-2012 01:36 PM in reply to: mojo2907

I would probably need to run this on my end to check out.  Could you email me your support share file to support@cfdesign.com?

 

To create a support share file go to File_Save Share File_Support Type.

 

If this is something you are willing to share you could also just post it to the forum.

 

Thanks,

Royce



Royce Abel
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Registered: ‎02-08-2012

Re: Setting up Compressible Flow

02-08-2012 02:02 PM in reply to: Royce_adsk

I will have to check and see if I am allowed to disclose model or not, and if I am, I will certainly do so as soon as possible. Unfortunatly, I wont be able to find out until tomorrow, and I will let you know. Thanks.