Afterbody separation control using passive porosity
Afterbody separation control using passive porosity
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DOI：
10.2514/6.1997-3003
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发表时间：
1997-07
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通讯作者：
Sandra L. Kraushaar;N. Chokani
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文献类型：
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作者：
Sandra L. Kraushaar;N. Chokani
本文进行了一项计算研究，以检验通过使用多孔表面对喷管后体流动的被动控制。三维Navier-Stokes方程求解器用于获得二维计算解。基线解决方案（无孔隙度），发现比较以及与实验数据。在亚音速、非设计状态下的被动控制，与基线情况相比，压力恢复略有损失。标称C渗透系数Cd排放系数，wp/w，Cp压力系数，（p-poo）/qoo FA轴向推力，NFi理想等熵推力，孔深与板厚之比，MOO自由马赫数，NPR喷嘴压力比，p <j/Poo P孔面积与总面积之比，多孔孔直径，m p局部静压，Pa pp增压室压力，Pa Pt，j射流总压力，Pa pw表面压力，Pa Poo自由流动静压，Pa goo自由流动动压，Pa t多孔板厚度，m vw蒸发速度，m/s Wf理想质量流率，kg/s wp质量流率，kg/s Xf多孔区域的完成位置，m '研究生研究助理，机械和航空航天工程系，学生会员AIAA。机械与航空航天工程系副教授，AIAA高级会员。版权所有© 1997年美国航空航天研究所，公司。All rights reserved. xs多孔区的起始位置，m fi分子粘度，kg/m-s p密度，kg/m111细网格序列122中网格序列144粗网格序列引言后体流的主要特征之一是分离。在亚音速流中，当附着流不能越过后体几何形状所施加的逆压梯度时，分离就发生了。在跨音速流动中，后体流动膨胀常常终止于激波，然后激波引起附面层分离。在任何一种情况下，分离都会引起粘性耗散和增加后体阻力。因此，后体上的附面层控制可以提供有益的阻力减小，这反过来又可以提高气动推斥效率。一种这样的附面层控制方法是通过抽吸进行主动控制。抽吸减小了边界层厚度，从而延迟或防止了流动分离。然而，主动控制方法是复杂的，并且通常，控制系统的附加重量可能是显著的。主动控制的另一种选择是被动控制。被动控制利用自然发生的现象来获得所需的流动特性。被动控制的优点包括系统简单、没有额外的重量和降低的成本。在这项研究中，被动孔隙度控制的概念进行了检查。如图1所示，这种控制方法使用多孔表面，该多孔表面位于压力梯度较大的区域中的增压室上方;在本例中，位于冲击波下方。激波后的高压区与激波前的低压区连通。版权所有© 1997年，美国航空航天研究所，公司。这种通信降低了冲击强度。冲击波强度的降低降低了其对边界层和流动分离的不利影响。以前的研究表明，被动多孔性方法可以通过减少或消除激波诱导和后缘分离来提高机翼在亚音速、跨音速和超音速时的性能。”在拱形前体上的试验已经证明了被动多孔性在亚音速和超音速时减小侧向力的能力。通过应用被动多孔性来减轻后体分离，也有可能减少飞机后体阻力。本研究的目的是通过计算来检验采用被动孔隙度的后体流动控制的有效性。
A computational investigation was conducted to examine passive control of a nozzle afterbody flow through the use of a porous surface. A threedimensional Navier-Stokes solver was used to obtain two-dimensional computational solutions. Baseline solutions (no porosity) were found to compare well with experimental data. Passive control at subsonic, off-design conditions had a slight loss in pressure recovery compared to the baseline case. Nomenclature C permeability factor Cd discharge coefficient, wp/w,Cp coefficient of pressure, (p-poo)/qoo FA axial thrust, N Fi ideal isentropic thrust, N H ratio of hole depth to plate thickness MOO freest ream Mach number NPR nozzle pressure ratio, p«j/Poo P ratio of hole area to total area d diameter of porous holes, m p local static pressure, Pa pp plenum pressure, Pa Pt,j jet total pressure, Pa pw surface pressure, Pa Poo freestream static pressure, Pa goo freestream dynamic pressure, Pa t thickness of porous plate, m vw transpiration velocity, m/s Wf ideal mass flow rate, kg/s wp mass flow rate, kg/s Xf finish location of the porous region, m 'Graduate Research Assistant,Department of Mechanical and Aerospace Engineering, Student Member AIAA. 'Associate Professor, Department of Mechanical and Aerospace Engineering, Senior Member AIAA. Copyright © 1997 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. xs start location of the porous region, m fi molecular viscosity, kg/m-s p density, kg/m 111 fine grid sequence 122 medium grid sequence 144 coarse grid sequence Introduction One of the main characteristics of afterbody flow is separation. In subsonic flow, separation occurs when the attached flow is unable to negotiate an adverse pressure gradient imposed by the afterbody geometry. In transonic flows, the afterbody flow expansion often terminates in a shockwave, which then induces boundary layer separation. In either case, separation causes viscous dissipation and increased afterbody drag. Hence, boundary layer control on an afterbody can provide beneficial decreases in drag, which, in turn, can improve the aeroprepulsive efficiency. One such means of boundary layer control is active control through suction. Suction decreases the boundary layer thickness, thus, delaying or preventing flow separation. However, active control methods are complicated, and often, the additional weight of the control system can be significant. An alternative to active control is passive control. Passive control makes use of naturally occurring phenomena to obtain desirable flow characteristics. Advantages of passive control include simplicity of the system, no additional weight, and reduced cost. In this study, the passive porosity control concept was examined. As shown in Figure 1, this control approach uses a porous surface placed above a plenum in a region with large pressure gradients; in this example, beneath a shockwave. The high pressure region behind the shock is allowed to communicate with the low pressure region ahead of the shock. Copyright© 1997, American Institute of Aeronautics and Astronautics, Inc. This communication reduces the shock strength. The reduction in the strength of the shockwave reduces its adverse effects on the boundary layer and flow separation. Previous research has shown that the method of passive porosity can enhance wing performance at subsonic, transonic, and supersonic speeds by reducing or eliminating shock-induced and trailingedge separation". Testing on ogive forebodies has demonstrated the capability of passive porosity to reduce side force at subsonic and supersonic speeds. There is also potential in reducing aircraft afterbody drag through the application of passive porosity to relieve afterbody separation. The objective of this study is to computationally examine the effectiveness of afterbody flow control using passive porosity.