I am performing CFD simulation over a NACA 4418 airfoil on Ansys FLUENT and I have collected a data chart of NACA (from 1945) for the purpose of validation.
The Reynolds Number chosen for this CFD simulation is 3,000,000 and the free stream velocity is 45 m/s. Since the simulation for my case is 2D simulation both the characteristics length and area is 1m. The value of y+ considered is 1 and that is ensured by calculating the wall spacing and putting that on First Wall thickness and I have even gone through Report in Ansys FLUENT to check the maximum facet value is below 1. I have used both Spalart Allmaras and K-omega SST Turbulence model. But the following problems are prevalent:
01. For Spalart Allmaras Turbulence model,my lift coefficient is within the range i.e less than 5% difference in between but drag coefficient is way too much high in value sometimes even 200% more
02. For K-omega SST Turbulence model, my lift coefficient is significantly higher in value and as Angle of attack increases this difference gets higher but the highest it gets is below 30% however drag coefficient is also over predicted but in this case the difference is around 50% higher.
I have tried it again for both Turbulence model with a bit more refined mesh but the value of lift coefficient increases in both the cases and but the difference for drag coefficient decreases for K-omega SST Turbulence model
I have been trying this for months now and haven't come to a proper solution. I tried everything at my disposal. Read aerodynamic books and gone through understanding how it is represented on CFD but so far I am not able to find the solution. If anyone can explain it to me what is going on for my case and how can I find a solution for this, that will be really helpful and appreciated.
In Fluent, for drag calculations, you must select the appropriate frontal area values in "Reference values", If not you answers will be off.
it may help you:
Article A full description of generalized drag in mixture mass flows
Best
Why are did you choose 3,000,000 as the Reynolds number? Way too high and practically not feasible. These values along with large diameter, density and velocity indicates a small viscosity of the fluid. Recheck your specifications.
Dear @Prosper Ovuoraye, I have done tried with Reynolds Number of 1,000,000 as well and even that was off
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