Computational Fluid Dynamics Evaluation of Bleed Slot of Purdue Mach 6 Quiet Tunnel

摘要

In this study a numerical analysis for the Purdue tunnel bleed slot design (case 7) is conducted for two stagnation pressures. For both of these conditions, recirculation bubbles are observed on the inner (nozzle) and outer (bleed slot) walls of the bleed slot lip. When the Langley tunnel is analyzed for the same order of magnitude stagnation pressure (96.6 kPa), no separation bubble is observed. Reverse flow regions are observed on both sides of the bleed slot lip for this tunnel, when the stagnation pressure is increased one order of magnitude (1034 kPa). The main conclusions of this study are as follows: 1) For the Purdue tunnel, our results show that as the inflow stagnation pressure increases the recirculation bubble formed on the inner (nozzle) wall becomes bigger. This suggests an explanation for observing quiet flow only for low stagnation pressures of 55.2 kPa for bleed slot design case 7 (Ref. 6). Based on the experiments of Klebanoff and Tidstrom, we thus conjecture that the small (0.37-mm) bubble at 56 kPa does not affect the stability properties of the nozzle wall-boundary layer, but the large (0.71-mm) bubble at 96.6 kPa destabilizes it. 2) Although the Langley tunnel computations displayed reverse flow regions on both walls of the bleed slot lip, the recirculation length is smaller than that seen in the Purdue tunnel computations. In addition, computations that yield separation for the Langley tunnel were performed at a stagnation pressure which is an order of magnitude higher than the stagnation pressures chosen for the Purdue tunnel computations. This might be caused by the position and shape of the bleed slot lip, but the size of the bleed slot lip must also be taken into account. The bleed slot tip diameter is three times smaller for the Langley tunnel. 3) To relate the relative size of the separation bubbles seen on the Langley and Purdue tunnels to the appearance of the premature transition of the tunnel wall boundary layer, an appropriate scaling must be developed.