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Negelecting Advection term in NS equations

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Old   October 29, 2012, 23:19
Default Negelecting Advection term in NS equations
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vaseem akram shaik
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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.
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Old   October 30, 2012, 03:07
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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.
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Old   October 30, 2012, 03:51
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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.
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Old   October 30, 2012, 04:27
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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.
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Old   October 30, 2012, 04:30
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Thanks again
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