Mathematical modeling and optimizationof flow structure in Francis turbine stage of microturbine power plant

This article presents information about the main distinguishing features of microturbine power plants and their advantages in comparison with other stand-alone sources of electricity. The justification of the use of Francis turbine in microturbine power plants with rated power of 100 kW is given. Initial analytical Engineering calculations of the turbine (without using computational fluid dynamics) with appropriate calculation methods are considered. The basic features of Francis turbine as a turbomachine, which operates a large heat drop with a high degree of reactivity are descripted. The approach to the definition of the geometry of the blade profile of turbine nozzles using arcs, Bezier curves and straight sections is given. For the parametric geometry in ANSYS program computational grid and calculation model were created. A parametric study of the flow in the nozzle was performed with various geometric configurations and the optimum configuration for the value of the speed ratio for different values of the angle of the output stream from the nozzle unit was determined (where the minimum of the range of angles under consideration is limited to manufacturing techno-logy). After exploring the nozzle the flow in turbine stage was studied (taking into account the flow in the impeller), for which limits of variation of geometrical parameters were also set and series of calculations were performed. The calculations determined the optimal geometry of the turbine stage on the criterion of maximizing efficiency. The calculation results are presented in graphical form, as well as the velocity and pressure fields at the interscapular channels of nozzle unit and the impeller.