Computation of the throat area of a turbine blade ring

Аннотация

The throat area is a geometric parameter of the blade ring necessary to profile its blades and compute the turbine capacity. As applied to the filament flow model, the area is defined by the involute of the throat solid figure onto the plane formed by the cascade throat located on one of the cylindrical sections of the blade ring and the radius. An equation is derived for computing the area of the involute, which considers the effect of the shape of the ring’s tailing outlines and the fillets at the transition from the outlines to the blade feather. Comparison of the area values for several turbines computed by the derived equation and by a more complex method based on a search for the minimum distances from the tailing edge of the blade to the suction surface of the neighboring blade in the channel revealed slight differences. The fluid-dynamic 2D analysis determined the radial boundaries of the filament bands, the parameters of the cascade that lie on a filament’s cylindrical surfaces, and the flow velocity normal to the throat section of the filament. The proposed approach to computation of the throat area is common for problems of both designing and analyzing the turbine operation and allows for excluding, in practice, methodological differences in determination of the flow rate and the flow angles at the outlet of the blade ring.