| Starting from computational fluid dynamics and by referencing the hydraulic design parameters of a hydropower station, the geometrical models of spiral case, stay vane, guide vane, runner, draft tube, and other flow passage components of this power station are established.According to the lower discharge capacity and lower efficiency during large flow rate of the original runner, the linear type crown is changed into arc type crown,meanwhile according to the unreasionable position design of the inlet edge and the outlet edge of the original vane,the outlet edge is moved to the outboard,which have increased the discharge capacity of the turbine and improved the energetic property during large flow rate. Structural grid is used for mesh generation of these models. Computational module in NUMECA software is used for the setting of boundary conditions and for solution computation. The distribution of velocity vector and static pressure in the flow passages of HL260 before modification and HL260A after modification are obtained through flow field analysis. Through analyzing the flowing state (including pressure distribution and velocity distribution) and through detailed comparing the pressure distributions of working face and rear face of the two runner blades before and after modification, we find that the variation of pressure gradient on the working face and rear face of the modified HL260A runner blade is uniform, centralized pressure zone does not exist on the head of working face and rear face, lower pressure zone does not exist on the zone in the blade rear face adjacent to the band.This provides references for the improvement of the hydraulic performance indexes by only changing the runner instead of changing the spiral case, stay vane, guide vane, the flow passage form and geometric dimension of the draft tube of the old power station. This also provides references and approaches for the current situation of the modification of old power station. |
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