Theoretical study of turbine stage characteristics in off-design conditions Free

The article deals with the theoretical analysis of the basic axial turbine stage characteristics. In the introduction, the analytical derivation of the stage efficiency is analysed, and the influence of the change of reaction, the velocity ratio u/cf and the absolute velocity exit angle from the stator blades are monitored. The next part consists of a 1D calculation in the middle blade radius with VT-400 (air turbine) input parameters, which is part of the experimental research at the Department of Power System Engineering. The calculation was carried out for 3 blading variants (low, medium and full reaction). Modes outside the turbine optimum operating point were induced by changing the velocity ratio u/cf, especially by changing the absolute isentropic velocity cf at constant circumferential velocity u. This action results in a change of the relative velocity vector flowing at the rotor blade. This leads to a redistribution of velocity triangles and causes additional losses (incidence losses).