基于重叠网格的唇口移动变几何进气道数值模拟研究

Numerical Investigation of Variable Geometry Inlet with Translating Cowl Based on Overset Grid

关键词:  冲压发动机  变几何进气道  重叠网格技术  气动特性  数值模拟

Key words:  Ramjet engine  Variable geometry inlet  Overset grid method  Aerodynamic characteristics  Numerical simulation

摘要:

为研究吸气式冲压发动机变几何进气道的气动特性及流动机理，采用发展的重叠网格技术，对变几何平动方式的进气道开展了数值模拟研究。针对存在物面接触重叠网格的挖洞操作在执行时无法取得合理的插值模板问题，引入了虚拟单元赋值方法和“Collar”网格方法，实现了多体相交时重叠网格的计算。为了引入“Collar”型重叠网格，对其算法作了适当修改以适应本论文所建立的洞面优化方法。对平移过程中内收缩比变化对启动过程的影响进行了研究。通过迎着来流方向平移唇口，增大了进气道的内收缩比，导致内压缩段出现边界层分离，分离泡随着唇口的前移而增大，当其移出内压缩段时，原本启动的进气道进入不启动状态，而后移唇口减小了内收缩比，使分离泡减小并向下游移动，辅以边界层排移，可以改善进气道的启动性能。此外，对平移速度和振荡频率对启动过程的影响也进行了研究，进气道迟滞效应随平移速度和振荡频率增大而增大。

Abstract:

In order to study aerodynamic characteristics and flow mechanism of the variable geometry inlet for air-breathing ramjet engines， the numerical simulation of inlet cowl translation for high Mach number variable geometry inlet is performed with developed dynamic overset grid. For overset grid of multiple bodies in contact with each other， the valid target cell may not be found in hole-cutting process. In order to solve this problem， the two improvement methods are proposed： the one is the introduction of traditional “Collar” grid， the other is the ghost cell method， thus the computation of overset grid with multiple bodies in contact is implemented. In order to introduce “Collar” to overset grid， appropriate modifications is done to accommodate overlap optimization algorithm. The effects of internal contraction ratio variations on starting characteristics caused by cowl translation are investigated. The calculated results show that with the moving forward of cowl， internal contraction ratio increases， the separation bubble moves upstream and moves out of the internal contraction segment， thus inlet unstarts. However， with the decrease of the internal contraction ratio caused by cowl moving backward， the separation bubble becomes smaller gradually and moving downstream which may improve the starting characteristics with a boundary layer diverter. The influences of translation velocity and oscillating frequency have significant effect on inlet performance. Moreover， the effects of translation velocity on the starting characteristics are studied and hysteresis effect becomes stronger with the increase of translation velocity and oscillating frequency.