侧滑角对V字形钝化前缘激波振荡特性影响

Effects of Sideslip Angle on Shock Oscillations of V-Shaped Blunt Leading Edge

关键词:  进气道  激波干扰  流动分离  高速纹影  图像处理  激波振荡

Key words:  Inlet  Shock wave interaction  Flow separation  High-speed schlieren  Image processing  Shock oscillations

摘要:

针对三维内转式进气道在侧滑状态下唇口处面临的非对称激波干扰问题，将唇口简化为V形钝化前缘，在来流马赫数为4的风洞中，采用高速纹影拍摄与壁面脉动压力测量，并辅以数值模拟，研究了半径比R/r=1（V形根部倒圆半径R与前缘钝化半径r之比）的V形钝化前缘在0°和2°侧滑角时的流动特性。结果表明，V形根部存在大尺度流动分离和分离激波振荡现象，并且这种振荡现象导致的壁面压力脉动对有/无侧滑非常敏感。与0°侧滑角相比，2°侧滑角时，迎风侧的分离区减小、振荡主频增加、脉动压力峰值显著升高，而背风侧的变化趋势则相反。有/无侧滑时，分离激波振荡主频经同侧的分离区尺度及直前缘激波后气流速度无量纲后，得到的斯特劳哈尔数均为St≈0.1，表明振荡现象均来源于沿壁面的逆流与来流之间的竞争机制。基于高速纹影图像的本征正交分解表明，无侧滑时，两侧分离激波振荡存在强耦合；而侧滑不仅会破坏这种振荡耦合，还使得前两阶振荡模态能量占比的差异性明显增大。

Abstract:

The cowl lip of three-dimensional inward turning inlet is simplified as a V-shaped blunt leading edge to reveal asymmetric shock wave interactions in the sideslip state. Flow characteristics of the V-shaped blunt leading edge with a radius ratio R/r=1 （the ratio of crotch radius R to the blunt radius r） at sideslip angles of 0° and 2° are investigated at a freestream Mach number of 4. High-speed schlieren photography and wall pressure measurements are adopted in the experiments and numerical simulations are performed. The results show that large-scale flow separations and shock wave oscillations occur at the V-shaped crotch and the fluctuating pressure on the wall is sensitive to the sideslip angle. Compared with those of the sideslip angle of 0°， the size of the separation decreases， the oscillation frequency increases， and the peak value of the fluctuating pressure increases significantly on the windward side of the sideslip angle of 2°. On the contrary， the variation trends of these parameters on the leeward side are opposite. When the oscillation frequencies of the separation shocks with and without sideslip are nondimensionalized by the separation length and the flow velocity behind the shock wave induced by the straight blunt leading edge on the same side， a nearly constant Strouhal number of St≈0.1 is achieved， which suggests that the origin of the oscillations is due mainly to the competition between the incoming flow and the reverse flow along the wall. The proper orthogonal decomposition based on high-speed schlieren images without any sideslip identifies a strong coupling between the shock oscillations on both sides. However， a small sideslip angle can not only destroy the original coupling but also enlarge the difference in the energy proportions of the first two modes.