Application of Uncertainty Quantication of Turbulence Intensity on Airfoil Aerodynamics

Abstract

Traditional CFD results have a number of freestream inputs. In the physical world, these input conditions often have some uncertainty associated with them. However, this uncertainty is often omitted from the CFD results. The effects of uncertainty in CFD can be determined through application of Uncertainty Quantification (UQ). The primary objective of the present work is to determine the effect of uncertainty in freestream turbulence intensity (FSTI) on the coefficients of lift, drag, and moment for four different airfoils: S809, NACA 0012, SC1095, and RC(4)-10. In this work, the Monte Carlo method is used to calculate the sensitivities of the aerodynamic coefficients to Gaussian distributions of uncertainty in FSTI over a range of angles of attack (AOA) at various Reynolds numbers and Mach numbers. However, the Monte Carlo method would require hundreds of thousands of CFD calculations in order to converge to the correct results. A surrogate surface is therefore generated using a parametric study using the in-house flow solver OVERTURNS. Rather than run a separate CFD run for each Monte Carlo run, all of the results can be attained virtually instantaneously via the surrogate surface.

The UQ analysis shows how varying these parameters affects the sensitivies of the aerodynamic coefficients to uncertainty in FSTI. In most cases, the response is nearly Gaussian and the mean response is not too dierent from the discrete FSTI response without uncertainty. However, the output standard deviation for drag and pitching moment can become large when the transition location changes rapidly with changing FSTI.