Mujeeb R. Malik, PhD

NASA Langley Research Center, Hampton, Virginia

We perform direct numerical simulations (DNS) to investigate the interaction of a turbulent boundary layer with the strong favorable and adverse pressure gradients generated by a Gaussian bump as the flow passes over it. The DNS has been performed using a high-order finite-difference solver for a spanwise-periodic bump configuration at the Reynolds numbers if 1 and 2 million, based on the bump length and the freestream flow velocity. Relaminarization for the lower Reynolds number case and flow separation in the higher Reynolds number case are investigated. A thin internal layer is generated beneath the original turbulent boundary layer as the flow accelerates over the windward side of the bump, which then evolves into a free shear layer in the deceleration region over the leeward side and subsequently separates due to the strong adverse pressure gradient. The data gathered from the DNS is examined to better understand the boundary layer response to the Gaussian bump in different regions of the flowfield. The results are also compared with the available experimental data. While the DNS required billions of grid points, wall-modeled large-eddy simulations (WMLES), with two orders of magnitude less resolution, are also performed and results compared with DNS and experiments. A new subgrid scale model is developed that improves flow prediction in separated flow region. Practical implications of accurate prediction of turbulent flows to aircraft certification by analysis are also addressed, which provides the motivation for this work.