可压缩自由剪切流混合转捩大涡模拟

针对湍流气动光学效应与冲压发动机气体混合机理问题,开展了可压缩混合层流动空间模式大涡模拟和时间模式直接数值模拟研究.通过对流场(包含亚/亚混合、超/亚混合两种情况)失稳、转捩直至完全湍流的空间发展过程的研究表明,对流Mach数0.4状态下流场失稳以二维最不稳定扰动为主;非线性发展中,基频涡对并及展向涡撕裂主控流动转捩,流场发生混合转捩;转捩后脉动流场基本达到局部各向同性,此时,湍流Mach数低于0.3,流动压缩性可近似忽略.

An analysis of transition coherent structuresin convective Mach Number 0.4 compressible free shear flow

The transition process and full turbulence mechanism of compressible mixing layers in convective Mach number 0.4 is investigated by spatial large eddy simulation (LES). The evolution of instable structures is analyzed. The numerical method is studied with a hybrid method of a fifth-order upwind compact difference and a sixth-order symmetric compact difference for the three-dimensional compressible Favre-filtered Navier-Stokes equations. The compact storage third-order explicit Runge-Kutta method is applied for time-integration. The sub-grid scales are formulated according to the modified Smagorinsky eddy-viscosity model. The instant and statistical parameters are discussed in detail, and the numerical results show a good agreement with the relevant literatures and theory. The computational results show that the most instable disturbance mechanism is mainly induced by 2-D wave perturbation in current convective Mach number. These results present that LES can simulate translation mechanism of mixing layers well.