Application of a continuous scale switch equation in steady and unsteady flow simulation

In order to get the higher precision of the unsteady flow predicted by using liner turbulence model as well as keep the capability of solving the steady flow, the Reynolds-stress term is combined with continuous scale switch equation(CSSE) to form one new stress term which can automatically adjust the local Reynolds-stress level according to the flow field scale, grid scale and Kolmogorov scale. The CSSE method eliminates the disadvantage of grid scale on the flow simulation, the problem of disagreement between the velocity profile obtained by the method of hybrid RANS/LES and the law of the wall is solved. Meanwhile, this method do not use the explicit sub-grid stress(SGS) model which can avoid the disadvantaged impact on the flow simulation caused by SGS coefficient, so the flow instability can be controlled more accurately. The simulations of the boundary flow of the plate and the flow over the cylinder both prove that CSSE method is robust. In the testcase of a turbulent flat-plate, the velocity profiles of flat-plate boundary layer solved by CSSE match with that solved by Reynolds averaged Navier-Stocks(RANS)method very closely, the simulation of cylinder wake proves that the CSSE method can precisely simulate the flow instability which is the advantage of hybrid RANS/LES.