topic Re: Problem with Temperature analysis in CFD Forum

Problem with Temperature analysis

Anonymous — Mon, 13 Sep 2021 07:24:22 GMT

I want to calculate the temperature drop due to Venturi effect (How hot air when passes from a hole of larger dia to a hole of smaller dia makes the air cool near the smaller dia).

I created a bounding box with air as material. At one side/surface of the box I applied velocity as 5m/s and temperature as 45 degree celcius. At the other end of box I applied pressure as 0 pascals.

But I could not see any temperature difference near the small hole and the temperature graph is flat. Both the lower and upper temperature is showing 45degree celcius. Please help me to resolve

Re: Problem with Temperature analysis

karol.suchon — Tue, 14 Sep 2021 13:26:51 GMT

Hello.

venturi effect is connected with the compressible flow, gas after decompression lost temperature. You also need to do that in Autodesk CFD.

Please check the article on how to set compressible analisys.

After that, it should work properly.

Regards,

Karol

Re: Problem with Temperature analysis

bob.schlosser — Tue, 14 Sep 2021 14:12:07 GMT

I do not believe Autodesk CFD is able to do this. (I have not verified that statement to be correct). I have been told by Autodesk support that the program does not solve based on the ideal gas law. The effect you are looking to simulate changes temperature because the pressure changes in the fluid. CFD will solve for pressure but the temperature is only solved as an effect of heat transfer and not changes in pressure or volume. I did verify this by simulating a closed box of air and changing the temperature. The pressure did not change. I suspect the reverse would also hold true.

Re: Problem with Temperature analysis

karol.suchon — Wed, 15 Sep 2021 14:23:29 GMT

Hello Bob,

you are right, the incompressible analysis does not use the ideal law to compute temperature change, it could be done only by heat transfer from source etc. It is just faster for the solver to calculate the most common problems, ideal gas law is used only in the subsonic, compressible flow analysis.

So using a subsonic solver we will be able to detect it, but I am not sure about the values, the solver was not created for that type of analsisys.

Below are some screens from the analysis.

regards,

Karol

Re: Problem with Temperature analysis

bob.schlosser — Wed, 15 Sep 2021 15:20:08 GMT

Hello Karol,

Thanks for the reply. I don't believe subsonic flow uses the Ideal Gas Law either.

Re: Problem with Temperature analysis

Anonymous — Wed, 15 Sep 2021 16:23:25 GMT

Hi Karol!

Firstly, Thank you very much for replying to my query. Can you please tell me the process and settings you did for the screenshots that you have shared. Should I need to just turn on the compressibility under physics tab? And by default it is showing total temperature as 26.85, What is the reason?

It would be helpful if you could write down the settings as pointers.

I am planning to apply the mechanism to a jali screen and run the analysis. Your reply would really help me.

Thanks in advance!

Re: Problem with Temperature analysis

karol.suchon — Wed, 15 Sep 2021 16:49:22 GMT

Hello Guys,

I asked about the issue my teammates and I need to agree with Bob.

The temperature field which I attach is connected with the velocity, not with the pressure change.

So we will not be able to simulate that effect in Autodesk CFD.

regards,

Karol