标题： 平面未膨胀冲击射流产生的壁面射流的相似性 显示英文标题

标题： Similarity of the Wall Jet Resulting from Planar Underexpanded Impinging Jets

摘要： 壁面剪切应力在喷嘴参数（离距高度、射流水力直径和喷嘴压力比）上进行映射，针对二维平面未扩展冲击射流。 计算流体动力学用于计算由冲击射流产生的流场，其高度与直径比为15-30，喷嘴压力比为1.2-3.0。 发现由未扩展冲击射流产生的壁面射流具有与传统壁面射流相同的三层次结构的自相似性。 发现可压缩性对壁面射流的影响可以忽略不计，对于马赫数小于0.8的壁面射流，无需对平均密度变化进行调整。 假设局部壁面射流变量具有源依赖系数的幂律关系。 发现通过动量进行归一化，而不是特征长度或源速度，有助于实现相似性。 开发了归一化最大速度、摩擦速度以及最大速度和半最大速度壁面距离相对于动量归一化的纵向位置的幂律关系。 使用共轭梯度法，将源依赖系数确定为喷嘴参数的函数。 这些幂律关系允许在一系列喷嘴参数范围内对冲击表面的壁面剪切应力进行完整映射。 显示英文摘要

摘要： Wall shear stress is mapped across nozzle parameters (stand-off height, jet hydraulic diameter, and nozzle pressure ratio) for two dimensional planar underexpanded impinging jets. Computational fluid dynamics is used to calculate the flow field resulting from impinging jets with height-to-diameter ratios of 15-30 and nozzle pressure ratios of 1.2-3.0. The wall jet resulting from underexpanded impinging jets is found to be self-similar in the same triple-layer structure as traditional wall jets. The effects of compressibility on the wall jet were found to be insignificant, and adjustment for mean density changes are not necessary for wall jets with Mach numbers of less than 0.8. Power laws with source dependent coefficient are assumed for local wall jet variables. It is found that normalizing by momentum, rather than characteristic length or source velocity, is beneficial for achieving similarity. Power laws for normalized maximum velocity, friction velocity, and maximum and half-maximum velocity wall distances versus momentum normalized streamwise location are developed. Source dependent coefficients are determined as a function of nozzle parameters using the conjugate gradient method. These power laws allow for complete mapping of wall shear stress on the impingement surface for a range of nozzle parameters.