Flow Interactions of Small Cylindrical Protuberances and the Supersonic Turbulent Boundary Layer on a Flat Plate

Abstract

This a combined experimental and computational study to evaluate the aerodynamic forces resulting from the interaction of small pin protuberances and the boundary layer of a flat plate in Mach 3.0 flow. Cylindrical pins with diameters of 2 mm and 6 mm were tested. The pin heights were 2 mm, 4 mm and 6 mm and they were tested on the flat plate with a turbulent boundary layer thickness of approximately 3 mm. The 2 mm diameter pin geometry was also tested in a group of four to assess mutual interference between neighboring pins. Oil flow, schlieren imagery, and pressure data were recorded on the nine pin configurations to capture a three dimensional understanding of the flow structures. The numerical results were calculated using a Reynolds-Averaged Navier Stokes code. The numerical results were compared to the experimental results for validation. Then they were used to predict the aerodynamic forces induced by a group of protuberances. This was a first step in assessing the possibility of using an array of independently deployable pin protuberances on a missile for flight control at supersonic speeds. Under this concept both the height and number of pins deployed could be controlled. The results showed that the scale of the upstream fluid structures is a function of the pin height to diameter ratio similar to previous studies. There were some fundamental changes in the flow downstream as the pin height was increased from within the boundary layer to outside the boundary layer. A periodic pressure of signal between 300 to 400 Hz was recordeded for all cases in the wake of the pin. The side force produced by the smaller pin ranges up to 1.2 N. The side force form the larger pin ranges up to 4.2 N. The drag forces for the smaller and larger pins ranged up to 0.87 N and 2.5 N respectively. To the first order the forces scaled to the product of the pin height and the combined width of the pins in each configuration.