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About the differences in results obtained from CFX and Fluent

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Old   December 23, 2023, 07:06
Default About the differences in results obtained from CFX and Fluent
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Ali Can
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Hello,

I am modeling cavity flow via 0.85 Mach and 6.5 million Re conditions. I want to calculate the aerodynamic forces (Fx, Fy, Fz) on the rear wall of the cavity. In this context, I am conducting my studies using both Fluent and CFX.

I am using the same mesh for both software. However, the results I obtained with Fluent and CFX are quite different from each other. Where do you think the problem might be?

I have specified my boundary conditions below.

Fluent

Operating pressure = 0
Inlet = pressure far field, 0.85 Mach, gauge pressure = 50000 Pa
Outlet = pressure far field, 0.85 Mach, gauge pressure = 50000 Pa
Second order discretization schemes
Ideal gas
SST k-w turbulence model

CFX

Reference Pressure = 0
Inlet = Inlet boundary condition-subsonic and velocity components are identified
Outlet = Outlet boundary condition – subsonic- averaged pressure/static pressure = 50000 Pa (I tried both)
Second order discretization schemes
Ideal gas
Shear Stress Transport model

I suspect that the issue lies in the definition of boundary or initial conditions, but I have not yet been able to pinpoint where the problem is.

Thank you,
Ryuzaki.

Last edited by Ryuzaki; December 23, 2023 at 14:16.
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Old   December 23, 2023, 15:54
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Glenn Horrocks
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Please show an image of what you are modelling and an image of the differences between your results.

But yes, your boundary conditions appear different. At the inlet you are using a pressure bc for the inlet in Fluent but a velocity bc for CFX. At the outlet fluent has constant pressure defined everywhere over the boundary but CFX has an averaged pressure defined - so the pressure can be higher and lower at locations, it is the average which is kept at your defined value.
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Old   December 27, 2023, 17:40
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As Glenn mentioned, you are NOT solving the same problem; therefore, nothing to compare.
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