The Numerical Study Of Prediction The Transition Location And Propagation Of Spanwise Disturbance Packet In A Boundary Layer

The phenomenon which is transition of laminar-turbulent exists broadly indiversified projects. The laminar flow and the turbulent flow have different characters.It is very important to predict the transition location of laminar-turbulent.In this paper, direct numerical simulation was adopted for the spatial evolution ofdisturbance by the coarse grid in a two-dimensional boundary layer on a flat plate. Wealso predicted the transition location based on the different amplitude disturbance atthe entrance. For the three-dimensional boundary layer, we studied the evolution ofspanwise disturbance packet at the entrance in the calculation region. We drew thefollowing conclusions:1. When the spanwise and streamwise velocity of free flow don’t depend on xand z, we can answer the similarity solution u and v firstly, and then get thevelocity w according the relation of spanwise and streamwise velocity. Sowe get the solution of the three-dimensional boundary layer equation.2. For the two-dimensional basic flow and that one finite amplitudetwo-dimensional T-S wave and two symmetrical three-dimensional T-Swaves were taken as the disturbers at the entrance, the disturbance evolutionwas simulated by coarse grid and the transition location was gained. Theresult indicated that when the amplitude of the two-dimensional T-S wavechanged form0.01to0.004, the transition location changed form350to520.The prediction the transition location can be studied by the coarse grid inorder to save calculational capacity.3. The eigenfunction and amplitude increase altered along with the differentvalues of the ratio of spanwise and streamwise velocity. When the ratiochanged form0.01to0.8, the u and v had tiny change and w changed smallfirstly and then changed big. The wavenumber in x decreased and thecurvature of increase ratio grew along with the values of ratio grew.4. The amplitude increase and disturbance evolution of wave package in thethree-dimensional basic flow accorded with the results which were get bythe theory of hydrodynamic stability. In this example, the propagationdirection of the peak value was a beeline and the angle with the x axis was0.29. This direction was consistent with the direction of the outer flow velocity.