激励小尺度模式在湍流圆管射流中的应用

采用非涡黏性的激励小尺度（Stimulated Small Scale)模式对空间发展的轴对称湍流圆管射流进行了大涡模拟。以雷诺数为10000的流动为例，考证了激励小尺度模式在自由剪切流模拟中的可行性，描述了湍流强度、雷诺应力和湍流耗散量的变化，同时与标准的Smagorinsky涡黏性模式的计算结果进行了比较。数值结果显示，激励小尺度模式能够更为合理地描述湍流的耗散特性和能量传输特性，从而较为准确地展示出空间发展射流中由于流动不稳定而出现的旋涡产生、发展、破碎及合并等过程。

APPLICATION OF STIMULATED SMALL SCALE MODEL IN TURBULENT ROUND JET FLOWS1)

The large eddysimulation of the axisymmetric turbulent round jet flow is presented.The non-eddy viscosity stimulated small scale (SSS) model is adopted tosimulate the spatially developing jet flow at a Reynolds number of10 000. The round jet flow is governed by incompressible, unsteadyNavier-Stokes equations in a cylindrical coordinate system and theprojection method proposed by Chorin is applied to solve them.Third-order and fourth-order compact finite difference schemes are used tocalculate the first and second derivatives in the convective and viscous terms respectively. The Poisson equation for the pressure issolved using the Gauss-Chebyshev transform in the streamwise directionand then solving the tridiagonal matrixes in the radial direction. Thetime integration is conducted by the third-order Runger-Kunter scheme. Theconvective boundary condition for velocity at the outlet is imposed toensure less effect of noise on the upstream flow. 　　A staggered gridarrangement is adopted, where the pressure and other scale variables aredefined in the center of the cell while velocity components are definedon the surfaces. Uniform meshes are used in the streamwise andcircumferential direction. The grid spacing in the radial direction isnonuniform with the grid points clustered near the jet orifice. Due tocomputational limit, the computational domain is taken equal to 25orifice diameters and 15 orifice diameters in the streamwise and radialdirection respectively. The grid system consists of 514 150 points in thestreamwise, radial direction, respectively. 　　The comparison between Smagorinsky's model and SSS model implies thatthe former model underestimates the turbulence intensity withSmagorinsky's constant of 0.1, while the results obtained by SSS modelshow a better agreement with the experiment. SSS model does not requirethe homogeneity and permits backscatter of energy fromsmall to large scales. Furthermore, it not only captures the dissipative natureof turbulence but also provides a good representation of instantaneousenergy transfer between the large and small scales. Hence, SSS model is ableto describe more exactly the generation, development and breaking of the vortexin round jet.