粗糙元诱导的高超声速转捩机理及应用

采用直接数值模拟（DNS）方法细致刻画了不同类型粗糙元诱导的高超声速边界层从层流到湍流的转捩过程，从拓扑结构稳定性和边界层流动稳定性两个角度分析了不同类型粗糙元诱导转捩的机理。通过对不同类型粗糙元诱导转捩机理的研究，设计了一种对齿型粗糙元，其具有小尺度、低摩阻、低热流、诱导转捩能力强的特点。研究发现不同类型的粗糙元底部区域均存在鞍点-结点-鞍点（SNS）型轨线，在扰动的作用下其会形成非定常、非对称的振荡结构。同时针对斜坡型以及对齿型粗糙元的工程应用开展了研究，验证了不同类型粗糙元诱导转捩的机理，为强制转捩装置设计提供了基础理论支撑。

Mechanism of hypersonic transition induced by a roughness element and its application

The physical mechanisms of hypersonic boundary layer transition induced by the roughness element are investigated by means of Direct Numerical Simulation (DNS) in terms of topological structure stability and boundary layer stability. Based on an analysis of the transition mechanism induced by roughness elements of different types, a new roughness element is designed. The new roughness element has the characteristics of small scale, low friction, low heat flux and easy to induce transition. The results show that all the base zones of the roughness elements of different types include a Saddle-Node-Saddle point (SNS) structure. Under the action of disturbance, the SNS structure forms into an unsteady and asymmetric oscillatory structure. In addition, comparisons are made between different types roughness (ramp and "gear" roughness), and transition mechanism of the different types roughness is analyzed, which supports design of hypersonic forced-transition device in the theory.