Uncertainty Quantification for Laminar-Turbulent Transition on Airfoil and Fuselage

The effect of uncertainty in Reynolds-Averaged Navier–Stokes (RANS) simulation is determined through application of Uncertainty Quantification (UQ). In the present study, the sensitivity of aerodynamic coefficients to uncertainty in freestream turbulence intensity (FSTI) and surface roughness is computed for both a rotorcraft fuselage (ROBIN- Mod7) and an airfoil (SC1095). Laminar-turbulent transition model has been extended to account for roughness- induced transition by incorporating an existing roughness-induced transition model. Current UQ analysis is based on the Monte Carlo method with Gaussian distributions of uncertain input parameters. The use of a surrogate model allows for incorporating the results from intensive RANS simulations into a Monte Carlo method. The surrogate model is generated using either a cubic interpolation for a single uncertain parameter or a radial basis function (RBF) for multiple uncertain parameters. The stochastic standard deviation is measured as an indicator for magnitude of uncertainty. It is observed that the standard deviation of each aerodynamic coefficient depends on the flow conditions (angle of attack, mean FSTI, and mean roughness) and the type of transition (natural or separation-induced). Also, the major source of output uncertainty is identified between the unknown FSTI and roughness at various flow conditions.