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Simulated CL higher than experiment (approx 4.8 vs 3)- wing in ground effect

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Old   December 24, 2022, 07:26
Default Simulated CL higher than experiment (approx 4.8 vs 3)- wing in ground effect
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I am trying to run a CFD simulation of the experiment described in this paper: Zhang and Zerihan. "Aerodynamics of a Double-Element Wing in Ground Effect", AIAA JOURNAL
Vol. 41, No. 6, June 2003. I am new to CFD. The mesh I obtained is shown in the attached screenshot. It has roughly 200k elements, triangle-dominant, I added inflations around the two airfoils and a rectangular body of influence. I added an inflation on the ground as well, where I need to simulate the belt used in the wind tunnel. At present, I am studying how the CL varies with respect to the heght of the arfoils from the ground, as presented in the paper. I attach both the results I am getting now and the experimental data. It can be seen how I am getting a general trend similar to the experimental one, but shifted upwards of 1.5 unit of CL, more or less. I am aware that I am comparing a CFD simulation with reality, and and an overestimation of Cl must be expected, but this looks way too far from real data, and I am aware that the steady simulation that I am running will never be equal to the real inevitably unsteady phenomenon. I am using Spalart-Allmaras model, an inlet velocity of 30 m/s (as in the paper), a turbulent viscosity ratio of 0.2% (as given in the paper), coupled solver, with 1st order scheme for momentum. I take from the simulation the lift, computed over the two elements surface, and then I nondimensionalize it using the chord (0.38 m) and a depth of 1 m which is the reference value of fluent for the depth, and the dynamic pressure as resulting from the inlet velocity.
I wonder what I could possibily be doing wrong, and what I could do to fix this issue. Thank you

Mesh zoom-in:

CL vs h/c from CFD simulation:

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cfd, fluent, ground effect, lift coefficient, wing

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