超声速边界层抽吸孔隙内流场结构分类

Classification of Flow Field in Supersonic Boundary Layer Bleed Slot

关键词:  流场结构  边界层抽吸  超声速  亚声速

Key words:  Flow field structure  Boundary layer bleed  Supersonic  Subsonic

摘要:

由于流体处于超声速和亚声速状态时，其性能有着显著的差异，这种现象同样存在于超声速边界层抽吸孔隙内。为了对超声速边界层抽吸孔隙内流场结构进行分类，主要通过数值计算的方法，对超声速边界层抽吸孔隙内流体的流动状态以及不同流动状态时抽吸孔隙内流场结构对抽吸腔反压的响应特点进行了研究，同时也对数值计算方法做了试验验证。数值计算采用基于有限体积法的二阶迎风格式来离散二维可压N-S方程，湍流模型采用标准k-ε模型，通过改变抽吸槽宽度D的方法来实现抽吸槽内流体处于不同的流动状态。根据抽吸槽内流体的流动状态的不同，将超声速边界层抽吸分为亚声速型，临界声速型和超声速型。分别对不同抽吸腔反压时三种抽吸类型流场结构变化特点以及声速流量系数Q变化特点进行了分析，发现不同抽吸类型对抽吸腔反压的响应规律存在显著差异。当δ/D>8.6时，即对于亚声速型抽吸而言，Q随δ/D减小而线性增加，且Q随[pc/p0]减小而减小。当δ/D<8.6时，即对于超声速型抽吸而言，Q随δ/D减小而迅速增加。另外，随[pc/p0]增加，Q先保持不变，当[pc/p0]增加到0.225时，Q开始减小，并且当[pc/p0]增加至0.675后，Q减小速率发生了突变。分析原因在于超声速型抽吸，抽吸腔反压向抽吸槽内的传递受到抽吸槽内分离区以及激波的阻碍，而对于亚声速型抽吸，抽吸腔反压能够直接传递至抽吸槽内，进而影响边界层抽吸。

Abstract:

There are marked differences when fluid is at supersonic state and subsonic state，which also exits in supersonic boundary layer bleed slot. In order to classify the flow field structure in the supersonic boundary layer bleed slot，the flow state in the bleed slot and the effects of chamber pressure on performance of boundary layer bleed under different flow conditions were investigated by means of numerical simulation. At the same time，experiment was made to verify the means of numerical simulation. Finite volume method based on second order upwind was employed to discrete two-dimensional compressible N-S equation and the standard k-ε model was chosen as the turbulence model. The fluid in the bleed slot can be controlled at different states by adjusting the width of the bleed slot (D). Based on the flow state of the fluid in the bleed slot，the boundary layer bleed can be classified into three types，namely supersonic-type，subsonic-type and critical-type. Finally，the flow field structure and sonic mass flow coefficient under a series of chamber pressure was discussed. It was found that response characteristics to the chamber pressure varied evidently when the boundary layer bleed type changed. When δ/D>8.6，namely at subsonic-type，sonic mass flow coefficient increased linearly with δ/D decreased and decreased with[pc/p0] decreased. However，when δ/D<8.6，namely at supersonic-type，sonic mass flow coefficient increased rapidly with δ/D decreased. In addition，sonic mass flow coefficient remains the same when [pc/p0] increased firstly. It begins to decrease until [pc/p0] increased to 0.225. Especially，when [pc/p0] increased to 0.675，the decrease rate of sonic mass flow coefficient changed suddenly. The reason of these phenomena is that for supersonic-type，the move of chamber pressure into the bleed slot is blocked by the separation zone and shock wave in the bleed slot; however，for subsonic-type，the change of chamber pressure can pass to the bleed slot quickly without clag，and then affect the boundary layer bleed.