Boundary Layer Response on Flat Plates with Triangular Porous Texturing Elements and Solid Triangular Prisms

This paper investigates how a canonical Zero Pressure Gradient (ZPG) flat plate boundary layer responds to an array of solid Triangular Porous Texturing (TPT) elements. Planar Particle Image velocimetry is used to measure the mean and fluctuating velocity fields from the wall to the boundary layer outer edge at freestream velocities U∞ = 10-30 m/s. Configurations with and without an upstream roughness trip isolate the roles of discrete tripping and distributed texturing. For tripped inflow, the TPT array primarily reshapes the inner layer. Relative to a smooth plate, it increases displacement thickness �∗, momentum thickness ��, shape factor H, and momentum thickness Reynolds number ���� �� while only modestly increasing the overall boundary layer thickness ��. In untripped flow, the TPT array acts as a distributed roughness trip that rapidly drives �� and ���� �� to or above the tripped smooth plate values over a shorter streamwise distance, yet maintains �� comparable to or smaller than that of the naturally transitioning baseline. Streamwise evolutions of the integral parameters show that the TPT geometry "front loads" the growth of �� and ���� �� and then sustains a fully turbulent inner layer within a compact outer edge characterized by elevated but nearly streamwise-constant H. These results show that millimeter-scale TPT elements can passively reorganize the near-wall momentum deficit and concentrate turbulent activity in the inner region, behavior that is consistent with passive flow control action and suggests potential skin friction and separation control benefits that call for further evaluation.