Learning Forum

[mikel]

Dear all,

I have one question about the boussinesq model aproximation and setting the operating temperature in operating conditions.

I am simulating a fluid flow with a temperature gradient (one inlet and two pressure outlets) and depending on the operating temperature that I use I obtain different results in my velocity profile. I apply a temperature of 300 K in the top part and 310 K in the top part, so my average temperature is 305 K. Then, I use three different operating temperatures (300 K, 305 K and 310 K) and I obtain the following results in the velocity contours of the fluid:

Operating temperature = 300 K

[DrAmine]

Operating / Reference temperature should correspond the expansion coefficient and density you provide under material properties.nI do not use Boussinesq Model anymore: it is something which was really valuable in the past. n

[mikel]

Hi again,nI understand your response but putting the temperature that corresponds to the expansion coefficient and density the results are not corrct.nIf I put a temperature gradient (300 K and 310 K) my average temperature is 305 K. Then in my reference temperature, I put 300 K because this is the temperature that corresponds the espansion coefficient and density of my material properties. Even so, as I show you previously, with an operating temperature of 300 K the results are not correct, I have a higher velocity in the top part (why can happen this ???) and to solve that I have to put the average temperature (305 K) in my operating temperature.nThanskn

[Karthik R]

Hi,nFirstly, Boussinesq model is applicable only if the density variation with temperature is small.nSecondly, is right! The operating temperature should correspond to the temperature at which you have defined your thermal expansion coefficient.nIf you are worried that Boussinesq is not giving you the right results, please use a different model for density - perhaps, an incompressible ideal gas?nKarthikn

[mikel]

Hi,nThanks for your response,nOn the one hand, I know that Boussinesq model is applicable only if the density variation with temperature is small, I think that this is one of that cases.nOn the other hand, my operating temperature corresponds to the temperature at which I define my thermal expansion coefficient, 300 K in my case. The problem is that the results whith that temperature are incorrect. The results of the velocity profile are correct only if in my operating temperature I put the average temperature of the gradient (305 K in that case).nI know that the result are not correct but I didnt know why occurs this, why the velocity profile changes depending on that operating temperature value. I can use also polynomial density depending on temperature but I want to know why occurs this with the boussinesq model.nDoes anyone know why this happens whith the boussinesq model?nThanksn