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vsmkrm298 October 29, 2012 23:19

Negelecting Advection term in NS equations
Hi Everyone,
I am trying to solve the Navier Stokes equations and continuity equation for low reynolds number flows, so i need to neglect the advection term compared to the other terms, so is this possible? If yes, please suggest the way to do this fluent. If not suggest other methods.

davidwilcox October 30, 2012 03:07

Hi vaseem,I would suggest putting in a sink term in the momentum equations. You would need to write a UDF for this though and compile it in Fluent. In that sink term, you could include the advection term. That way, it cancels out the advection totally. Just a suggestion.

Hope this helps. :)

vsmkrm298 October 30, 2012 03:51

Hey thanks for the help. The actually question is not about neglecting the advection. I am trying to solve unsteady navier stokes equation at microscale, so i non-dimensionalised these equations, but the coefficients of advection term and unsteady terms are not same, so i am confused about giving the density value for these equations, infact i tried to do the non-dimensionalisation so that both the coefficients match, but my mentor said that there will be a problem if i do this way. So can help me about this? btw i am familiar with the udfs.

davidwilcox October 30, 2012 04:27

I'm assuming that you're not including any body forces acting on the fluid. So your Momentum equation in non-dimensional variables should look like this:

Rho* D(v_i)*/Dt* = -d_i*p*+d_j*tau_ji*
where v_i* = v_i/vo (velocity scale);
p* is just your coefficient of pressure and Rho* takes on a value of 1.

What you can do... and i'm not sure but it's worth a shot, is to run the simulation as per norm and then extract the individual variables, gradients, etc from the momentum equations and then do your non-dimensionalizing. Not sure if this will help you in what you want to achieve though.

vsmkrm298 October 30, 2012 04:30

Thanks again

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