Research of radiality degree effect on stream structure in a flow range of radial-axial turbine in a gas-turbine plant

The relevance of the work is caused by the necessity to improve a flow range of the radial-axial turbine of new generation of gas-turbine plants, applied in various industries. Microturbines with electric capacity from 15 up to 600 kW, with oil gas as fuel, are the separate group of low power gas-turbine plants. The aim of the work is to investigate the influence of radiality degree on stream structure in the flow range of the radial-axial turbine with 140 mm driving wheel by means of Ya.A. Sirotkin model of axissymmetry vortical current of a nonviscous compressed liquid in the flow range of radial-axial turbomachines. Methods of research: Ya.A. Sirotkin method for calculation axissymmetry vortical current of nonviscous compressed liquid in the flow range of radial-axial turbomachines. Results. The paper introduces the issues of a choice of radiality degree of the radial-axial turbine of the low power gas-turbine plant. Based on the method of Lagrange uncertain multipliers the authors have designed the driving wheels of the radial-axial turbine with radiality degree m=0,47, m=0,52, m=0,57. The analysis studies on the influence of radiality degree on characteristics of the radial-axial turbine were carried out. The paper introduces the characteristics of turbines on the efficiency and on capacity in the stationary stream, obtained on the basis of the method for calculating a turbine on average radius. Based on these characteristics it is shown, that the turbine efficiency and capacity grow at reduction of radiality degree. The influence of radiality degree on the stream structure in the flow range of the radial-axial turbine is shown. As a result of calculation of axissymmetry flow in driving wheels, the distributions of meridian speeds depending on a normal length and distribution of relative speed along the lines of meridian contour of driving wheels are resulted. The zone of return currents was determined on the basis of these distributions. The paper introduces the results of calculation of current surfaces. The border of the return current zone is determined under condition of ws=0. In all computational regions the error in the speeds ws was amounted less than 1 %. After calculation of the stream structure by the Ya.A. Sirotkin model it is shown, that reducing the radiality degree the zone of return currents increases, despite of high efficiency determined by the model of calculation on average radius. The paper introduces the experimental and design distribution of absolute speeds at the output of the turbine driving wheel with the radiality degree m=0,57. The comparison of the results of calculation of axissymmetry current by the method of Ya.А. Sirotkin with the experimental results shows, that there is an insignificant divergence of the experimental and design values of the absolute speeds in radical and central areas of the stream.