Rough Wall Boundary Layer Development in Response to Changing Pressure Gradients

Experiments were conducted in non-equilibrium turbulent boundary layers on a rough flat wall. The test section included a zero pressure gradient (ZPG) development region, followed by a favorable pressure gradient (FPG) region with constant acceleration parameter K=(ν/U_∞²)(dU_∞/dx), a ZPG recovery, and a constant K adverse pressure gradient (APG) region. Eight cases were documented with three different inlet velocities and K in the FPG ranging from 0.125×10^-6 to 2×10^-6. The K magnitude of the APG in each case was half that of the FPG. Velocity profiles were acquired at 12 streamwise stations using a two component LDV, and PIV was used to document velocity fields at the same stations. Turbulence statistics and two-point correltations of the turbulence quantities were computed. Experiments were completed and documented previously with a smooth wall under these conditions.  In the present work, a wall with mathematically generated stochastic roughness was produced by additive manufacturing, and new experiments were done under the same conditions as in the smooth wall cases.  A subset of the data will be presented to show the response of the rough wall boundary layer to the changing pressure gradient, and similarities and differences from the smooth wall cases will be examined.