Optimization of the turbine diffuser of a multipurpose microturbine

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One of the applications of microturbines is their use as part of a hybrid transmission. This will significantly improve the environmental friendliness of vehicles. One of the problems of microturbines with a radial turbine and heat exchanger is the effective braking of the gas flow behind the turbine in the turbine diffuser. The purpose of this paper is a design study of the flow of gas in diffusers of various designs in order to determine the optimal (for losses of the total pressure and uniformity of the velocity field) structure. For the study, two variants of the layout of the microturbine were taken. In the first case, the axis of rotation of the heat exchanger was located parallel to the axis of rotation of the impeller of the turbine stage, in the second case - perpendicular. In order to minimize losses, the geometry of the output device of the first variant of the arrangement of the microturbine was varied, in particular, the output device without and with deflectors was considered. From the results of calculations it follows that the introduction of deflectors into the geometry of the output device makes it possible to reduce the vortex formation and, correspondingly, the total pressure loss. To determine the loss and the optimal value of the diffuser opening angle, a series of flow computations in the stage of the radial-axial turbine with a variation in the slope angle of the upper generator of the output diffuser α (0.0°, 2.5°, 4.0°, 6.0°, 7.0°) were conducted. A preliminary study was made of the effect of the selected model of turbulence and the size of the grid on the results of the calculation. Analysis of the results of calculations showed that the minimum losses of the total pressure and the maximum increase in static pressure are provided by the diffuser with an angle of inclination of the upper generatrix of 6°. An increase in the angle of inclination of the upper generatrix of 7° leads to developed detachment currents and an increase in losses. A comparative analysis of the obtained data for different versions of the diffuser showed that the second version of the layout of the microturbine (with a straight circular annular baffle diffuser) has significantly lower total pressure losses in the turbine output device.