Learning Forum

[josht]

I am trying to get a drag coefficient. For some reason, I am getting a number that doesn't really make sense. I will place the pictures of what I did.

[Karthik Remella]

Hello,nDo you have a converged solution? Please share plots of your residuals and drag / lift coefficient as a function of iterationsnWhat reference values are you using?nDo you have sufficient resolution in your boundary layer mesh?nThe lift and drag coefficients in such simulations are very dependent on all of these questions. Please double check these and see if they address your issues.nThanks.nKarthikn

[josht]

I believe I do have a converged solution. Im not sure how to get the drag/lift coefficient as a function of iterations. How do you do it? Here are the residuals:nReference values: nHere is the mesh quality information. I used the evaluate mesh quality button on fluent. nn

[DrAmine]

Mesh resolution is not enough. Residuals are still high and reference values need to be adjusted as reference area and density and velocity are to get dimensionsles parameters n

[josht]

How do I improve the mesh quality? So I need to manually change the reference surface area? It doesnt automatically get changed with the geometry? What does it mean that the residuals are high? Im confused on why velocity and density need to get dimensionless parameters. Im really new to Ansys and would appreciate it if you could help out. n

[DrAmine]

The definition of drag coefficient requires a reference area as well as a reference stagnation pressure.nnImprove mesh in preprocessing. The wall is very coarse.nnYour residuals are high. Moreover at that speed I will include turbulence modeling.n

[josht]

I still dont know what high residuals means. Why is turbulence modeling necessary? n

[Karthik Remella]

Please see the residual plot. Your continuity, momentum, and energy residuals are high. They should, for a good converged solution, go down by at least 3 orders of magnitude. nWhat is your inlet Reynolds number? nThanks,nKarthikn