圆柱型粗糙元诱导的超声速边界层转捩实验研究

Experimental Study of Supersonic Boundary Layer Transition Induced by Cylindrical Roughness Elements

采用纳米粒子示踪的平面激光散射(NPLS)技术研究了马赫数为3.0条件下,不同高度和不同数量的圆柱型粗糙元诱导的边界层转捩过程.获得了超声速流动中圆柱型粗糙元诱导的边界层的流向和展向精细流场结构.观察到了粗糙元尾迹边界层的发展过程,再附后的边界层将在一定范围内保持稳定.同时,在边界层发展过程中观测到了清晰的发卡涡结构.利用分形理论对边界层NPLS图像进行定量分析,获得了几种情况下边界层转捩的位置.研究结果表明,多个粗糙元间的相互作用能够抑制边界层的转捩以及尾迹中发卡涡的演化.然而,当两侧粗糙元高于中间的粗糙元时,粗糙元间的相互影响对于尾迹边界层发展的抑制作用反而不明显.

The boundary layer transition process induced by different heights and quantities of the cylindrical roughness elements at Mach 3.0 is investigated experimentally by using the nano-tracer-based planar laser scattering(NPLS)technique.Fine structures of the boundary layers of both streamwise and spanwise induced by the cylindrical roughness elements in the supersonic flow are obtained,and the development of the boundary layer in the roughness element wakes is observed.The boundary layer after reattachment will keep the laminar state within a certain distance,meanwhile hairpin vortexes can be observed clearly during the development of the boundary layer.The fractal theory is used to quantitatively analyze the NPLS images of the boundary layer.This method can achieve the positions of the boundary layer transition in several cases.The research results show that the interaction between multiple roughness elements can inhibit the boundary layer transition and the evolution of hairpin vortexes.However,when the roughness elements on both sides are higher than those in the middle,the interaction between roughness elements has no obvious inhibitory effects on the development of the boundary layer.