Direct numerical simulation of boundary layer turbulence

In this study, the regeneration mechanism of hairpin-like coherent flow structures in transitional and turbulent boundary layers induced by the presence of riblets is investigated. According to previous studies, delaying transition the breakdown to turbulence and drag reduction by the riblets is observed compared to smooth surface. To know how the riblets change shape and dimensions of hairpin vortices will be helpful to understand how this coherent flow structures provide the effects like drag and noise reduction and delaying transition. To contribute all of these studies, a numerical study is designed that creates a turbulent spot triggered in a zero-pressure-gradient laminar boundary layer by a pulsed, transverse jet. A direct numerical simulations (DNS) is applied to observe the growth of the spot into a turbulent region. The accuracy and results of simulations are controlled by comparing the flow features over the smooth surface with the results of the previous direct numerical simulation.