Starting characteristics of supersonic inlets-猫眼课题宝

DOI：

10.2514/6.1996-2914

发表时间：

1996-07

期刊：

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

D. Wie;F. Kwok;R. Walsh

在标称马赫数为3的条件下，研究了一种具有厚进气边界层的小尺寸矩形进气道的起动特性。研究的参数包括雷诺数，长度和高度。测量了最大收缩率和再开始收缩率。根据测试配置，不启动被分为两大类，要么是“硬”或“软”。“当入口喉部的气流阻塞时，似乎会发生硬起动。当进气道内出现大规模分离时，会发生软不起动。经典的Kantrowitz极限的能力，以预测重新启动收缩比进行了评估，它被证明是适用于硬unstart/重新启动配置。还评估了未启动入口上游流体喷射的作用。这种喷射的使用可能最终导致改善进气道的起动特性。标称A面积hc整流罩高度Lc整流罩长度rh质量流量M马赫数M质量平均马赫数P压力Pt自由总压x，y笛卡尔坐标y比热比6边界层厚度6* 边界层位移厚度0边界层动量厚度9 C整流罩角度p密度 * 首席工程师，高级成员AIAA ** 高级工程师，版权所有©美国航空航天研究所有限公司，1996. All rights reserved.下标0自由进气道2进气道4进气道喉部cl进气道进气道喷射时的壁面条件介绍工作在超音速和高超音速下的吸气式发动机需要进气道来捕获和压缩空气，以便由发动机的其余部分进行处理。任何进气道设计的目标都是确定最小重量的几何形状，以提供有效的压缩过程，产生最小的阻力，产生进入压气机或燃烧室的几乎均匀的气流，并在广泛的飞行和发动机工作条件下提供这些特性。为了有效地工作和适度的诱导阻力，大多数进气道采用外压和内压的组合。在进气道中引入内部收缩增加了设计和分析过程的复杂性，因为必须确保进气道的启动。为了有效地工作，超音速和高超音速进气道必须在启动模式下工作。进气道启动和不启动的过程在概念上已经很好地理解了，尽管重要的细节仍有待解决。在起动进气道的定义中存在着一些变化。一种惯例认为，起动的进气道是在进气道喉部有超音速流的进气道，但众所周知，某些未起动的进气道可能具有复杂的内部流场，在进气道喉部有很大一部分超音速流。在本工作中，术语“启动”用于表示在进气道内部的流动现象不改变进气道的空气捕获特性的条件下的操作。（在评估是否启动入口时，不考虑通过使用泄放孔或旁通通道减少捕获的质量流量。）进气道可以通过过度收缩到进气道喉部的气流阻塞点或通过将背压升高到进气道可以承受的水平以上来停止启动。目前，关于进气道将不启动或重新启动的条件存在很大的不确定性。这种不确定性的部分原因是由于在设计发动机时所考虑的美国航空航天研究所的几何形状种类繁多。进气道的设计受飞行器因素的影响很大，已经研究了各种二维平面、轴对称和三维进气道设计。进气道设计的多样性可从图I所示的样品进气道中看出。“可以从Kantrowitz极限得到内部收缩的初步估计。这个极限是通过假设在内部收缩开始时有一个正激波，并计算将在进气道喉部产生音速流的一维等熵内部面积比来确定的。对于理想气体，Kantrowitz极限可以计算如下：

The starting characteristics of a small-scale rectangular inlet with a thick ingested boundary layer were investigated at nominal Mach 3 conditions. Parameters investigated included Reynolds number, cowl length, and cowl height. Measurements of the maximum and restart contraction ratios were made. Depending on the test configuration, the unstarts were classified into two broad categories as either "hard" or "soft." The hard unstarts appear to occur when the flow at the inlet throat chokes. The soft unstarts occur as large-scale separation develops within the inlet. The ability of the classical Kantrowitz limit to predict the restart contraction ratio was assessed, and it was shown to be applicable for the hard unstart/ restart configurations. The role of fluid injection upstream of the unstarted inlet was also assessed. The use of this injection may ultimately lead to improving the starting characteristics of inlets. Nomenclature A Area hc Cowl height Lc Cowl length rh Mass flow M Mach number M Mass-averaged Mach number P Pressure Pt Freestream total pressure x, y Cartesian coordinates y Ratio of specific heats 6 Boundary layer thickness 6* Boundary layer displacement thickness 0 Boundary layer momentum thickness 9C Cowl angle p Density * Principal staff engineer, senior member AIAA ** Senior staff engineer, member AIAA ^ Associate staff engineer, member AIAA Copyright © American Institute of Aeronautics and Astronautics, Inc., 1996. All rights reserved. Subscripts 0 Freestream 2 Entrance to cowl 4 Inlet throat cl Wall conditions at cowl lip inj Injectant Introduction Airbreathing engines that operate at supersonic and hypersonic speeds require inlets to capture and compress air for processing by the remainder of the engine. The goal in the design of any inlet is to define a minimum weight geometry that provides an efficient compression process, generates minimum drag, produces nearly uniform flow entering the compressor or combustor, and provides these characteristics over a wide range of flight and engine operating conditions. For efficient operation and moderate induced drag, most inlets use a combination of external and internal compression. The introduction of internal contraction in an inlet adds complexity in the design and analysis process in that the starting of the inlet must be ensured. For efficient operation, supersonic and hypersonic inlets must operate in a started mode. The process of inlet starting and unstarting is well understood at a conceptual level, although significant details remain to be resolved. Some variation exists in the very definition of a started inlet. One convention states that a started inlet is one with supersonic flow in the inlet throat, but it is well known that some unstarted inlets can have complex internal flowfields with a significant fraction of supersonic flow in the inlet throat. In the present work, the term "started" is used to denote operation under conditions where flow phenomena in the internal portions of the inlet do not alter the air capture characteristics of the inlet. (Reduction in the captured mass flow through the use of bleed holes or bypass channels is not considered in assessing whether an inlet is started.) An inlet can be unstarted by either over-contracting to the point where the flow chokes at the inlet throat or by raising the back pressure beyond the level that can be sustained by the inlet. Currently, a significant uncertainty exists regarding the conditions under which an inlet will unstart or restart. Part of this uncertainty is due to the large variety of 1 American Institute of Aeronautics and Astronautics geometries that have been considered in designing engines. The design of an inlet is strongly affected by vehicle considerations, and a variety of two-dimensional planar, axisymmetric, and three-dimensional inlet designs have been investigated. The diversity found in inlet designs can be seen in the sample inlets shown in Fig. I.'" Preliminary estimates of the internal contraction that will self-start can be obtained from the Kantrowitz limit. This limit is determined by assuming a normal shock wave at the beginning of the internal contraction and calculating the one-dimensional, isentropic internal area ratio that will produce sonic flow at the inlet throat. For a perfect gas, the Kantrowitz limit can be calculated as follows: Oswatisch inlet HRE-type inlet A2] /KANTROWITZ M, l)MJ

Starting characteristics of supersonic inlets

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