# high lift coefficient and weird pressure coefficient on cfd fluent

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keans0018 posted this 3 weeks ago

i had a very high lift coefficient and the pressure coefficient does not looks right. This is the fluent setup: 1) i am using C-domain with 40,000 mesh elements with 40,400 nodes. 2) i am using density-based since i am doing a test with high speed flow where the mach number is above one. 3) model: k-epsilon standard. 4) Air properties, density is in ideal-gas. 5) Cell-zone condition: the pressure gauge is 101325 Pa 6) i am using pressure far-field, the inputs are: 0 pressure gauge; Mach = 2 ; AOA = 1 degree. 7) the solution methods and controls remain default. 8) i ran the iteration between 500-1000

This were the method i get the lift coefficient. Under the Reports > Forces > x ( -ve sin 1) ; y (+ve cos 1). This will print out on the console, and the lift force was about 11 KN, i will put this value into excel and calculate the lift coefficient by rearranges the lift equation. which is about Cl= 11.0 ++

I am seeking for help from my lecturer, he can't help me either since he is not familiar in supersonic flow conditions.

The Lift force: 11,342.087 N, its very high... really needs help

Raef.Kobeissi posted this 3 weeks ago

Whats the dimensions of the airfoil? Did you make sure you set the case with the right units? How does your residual error plots look like, could you attach a picture of it + velocity contour please.

Best Regards

Raef Kobeissi

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keans0018 posted this 3 weeks ago

what do you mean about the right units ? would you mind to mention more specific for the word " right units" ? the chord length of this 2D biconvex airfoil is 1meter, the thickness is 6%.

keans0018 posted this 3 weeks ago

i am not sure this is the residual error plot that you mentioned before. i really need your help, since i tried different way, all i need is how could i find lift,drag and pressure coefficient. i knew this pressure coefficient is completely wrong.

keans0018 posted this 3 weeks ago

ok i got my mistakes now, i forgot to change the velocity from my equation, that's why my lift coefficient went wrong. Thanks anyway.