Bruce Dan Bouldin

EXPERIMENTAL MEASUREMENT OF BOUNDARY LAYER FLOW WITH SUCTION INTO A HONEYCOMB PANEL

Experiments were conducted in a low speed laboratory wind tunnel in order to characterize boundary layer flow that is subjected to suction as it flows over a honeycomb section of the wall. The problem arises in the design of filtered inlets to engines in aerodynamic applications. The honeycomb was baselined in a traditional orientation normal to the flow direction. The overall total and static pressure drops and the downstream velocity field were measured using pressure probes and wall static taps upstream and downstream of the honeycomb. The wind tunnel was then re-configured so that the main wind tunnel flow resembled an infinite free-stream approaching the honeycomb inlet at 90° from the normal. It was determined that the radius of curvature of the flow stream entering the honeycomb is small in the upstream region of the honeycomb, and increases monotonically in the flow direction. This inviscid effect causes a drop in the static pressure in the upstream region of the honeycomb followed by a gradual recovery of the static pressure in the flow direction. The local mass flow ingested through the honeycomb consequently is low in the forward section and increases monotonically in the flow direction. In addition to this inviscid mechanism, we observe non-uniformity of the pressure loss coefficient over the honeycomb panel, which is attributed to viscous mechanisms. The total pressure loss coefficient, K, is found to vary from a value of roughly 1.2, for grazing angle of 5° in the forward section of the honeycomb, to 0.9, for a flow approaching from the direction normal to the inlet. It is hypothesized that the increased total pressure loss for the grazing flow is due to stagnation and flow separation at the inlet of each honeycomb passage.Copyright