# Why the lift and drag coefficients for the simulations differ from the experimental value?

I am doing CFD simulations for NACA Airfoil 2415 using K-Omega SST model on ANSYS fluent. I am using an tetrahedral unstructured mesh with 20 Inflation layers on the wall. I have been comparing my result with the experimental data found in NACA 460 report. What I notice is that the values which I get using simulations are higher in comparison to the experimental data. The Reynolds number for which I am simulating is 3 million. Any reasons why the difference is?

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091108.pdf

• Small differences between the simulation and the reality are to be expected. How big is the difference you observe? – DeltaLima Sep 23 '19 at 12:24
• As an example for 10 degrees AOA, the experimental Cd is around 0.02 while I am getting around 0.06 with the CFD Model. The difference is small at lower angle of attacks and the differences get large with high AOA. – Ashish Tiwari Sep 23 '19 at 12:33
• @Ashish Tiwari Is it possible, based on higher differences at higher AOA, that your simulator is calculating induced and parasite drag, while the NASA is only counting induced drag? Are they both using infinite AR (limited AR would include wing tip drag, which increases with higher AOA). I would check if raw data generation was "on the same page" – Robert DiGiovanni Sep 23 '19 at 13:58
• Is the error also linear with $\alpha$? I would start by trying to isolate the source of the disparity. – AEhere supports Monica Sep 23 '19 at 14:22
• – ymb1 Sep 23 '19 at 14:54