Three-Dimensional Computational Model for Flow in an Over- expanded Nozzle with Porous Surfaces

A three-Dimensional computational model is used to simulate flow in a non-axisymmetric, convergent-divergent nozzle incorporating porous cavities for shockboundary layer interaction control. The nozzle has an expansion ratio (exit area/throat area) of 1.797 and a design nozzle pressure ratio of 8.78. Flow fields for the baseline nozzle (no porosity) and for the nozzle with porous surfaces of 10% openness are computed for Nozzle Pressure Ratio (NPR) varying from 1.29 to 9.54. The three dimensional computational results indicate that baseline (no porosity) nozzle performance is dominated by unstable, shock-induced, boundary-layer separation at over-expanded conditions. For NPR!1.8, the separation is three dimensional, somewhat unsteady, and confined to a bubble (with partial reattachment over the nozzle flap). For NPR"2.0, separation is steady and fully detached, and becomes more two dimensional as NPR increased. Numerical simulation of porous configurations indicates that a porous patch is capable of controlling off design separation in the nozzle by either alleviating separation or by encouraging stable separation of the exhaust flow. In the present paper, computational simulation results, wall centerline pressure, mach contours, and thrust efficiency ratio are presented, discussed and compared with experimental data. Results indicate that comparisons are in good agreement with experimental data. The threedimensional simulation improves the comparisons for over-expanded flow conditions as compared with two-dimensional assumptions. Introduction A clear understanding of the flow in an over-expanded nozzle with porous surfaces is important because it sheds light on the complicated relationship between overexpansion, shock-induced separation, passive control, and thrust efficiency. An accurate tool to model the above mentioned phenomena is of critical importance. Investigations in the area of Passive Porosity Technology (1-10) for propulsion applications have led to an https://ntrs.nasa.gov/search.jsp?R=20070003596 2018-03-26T22:55:17+00:00Z