Numerical Investigation Of Unsteady Vortex Flow Fields In A Draft Tube

Commercial softerware-CFX5.5 was used in this paper. Based on Reynolds equations closed by k-εturbulence model,the numerical simulation of three-dimensional unsteady and steady turbulent flow was conducted under different operating conditions,achieving flow filed in the draft,vortex rope and frequency with fluctuation range,which was carried out in the model draft of a power station. The main research findings were as follows.The flow state at the draft tube inlet was specially discussed,suggesting the method of giving inlet boundary of draft, and then periodicity circumvolve inlet was modeled,achieved by User Fortran. The result clearly reappearances vortex movement at the part load condition and flow field and pressure distribution in the draft tube under different conditions,which were much more rational and similar to practical experiment results,and which assure that the inlet velocity model is very close to the authenticity.By comparing two simulation results with pier and without pier,it was assured that pier have no obvious effect to improve flow state and restrain vortex rope under condition of part load,but which can sharply decrease pressure value of fluctuation.It is obvious for the pier action from the extent to smooth flow line as sets runs optimum working condition.Also, outlet tank have a good effect to convergence in the process of calculation. And also, the rectangle at the tail of pier was remodeled to cylinder face before CFX-solver working, which can obviously improve the boundary conditions at the draft tube outlet and contribute to increase convergence.By simulation of three-dimensional unsteady turbulent flow at part load condition,the results show that the max compressive stress occur at the underside of cone part closed by bend.At the same time,the fluctuation frequency accorded with times frequency rule very well.