Selection of the Radial-Axial Turbine Design Methods for the Piston Engines
The paper provides rationale for the need to select a mathematical model supplemented by empirical formulas to calculate the kinetic energy losses making it possible to determine the gas-dynamic and energy characteristic values of a turbine stage at the average radius with accuracy sufficient for the practical use. Theoretical substantiation is presented of eligibility in using results of calculation performed for the gas-dynamic characteristics, which numerical values are typical for the average radius of the designed turbine meridional section. A way of improving the one-dimensional calculation methods for optimizing the turbine stage is presented. It includes the method of indefinite Lagrange multipliers (efficiency factor depending on the characteristic number and the degree of reactivity is taken as the target function); selection of the optimal dimensions of the impeller and rotor blades; accounting for the influence of gas flow non-one-dimensionality in the outlet section on its gas-dynamic characteristics; accounting for phenomena in interventional gaps and labyrinth seals; constructing meridional bypass of the flow path. It is shown that these methods with appropriate addition of the empirical dependencies making it possible to determine the loss in gas kinetic energy and taking into account the interblade channels configuration could be used to calculate the gas-dynamic parameters of turbines.