4.7. Optimization design of radial inflow turbineThe numerical calculation of the turbine is carried out using theoptimized nozzle and rotor models. The total-to-static efficiency is usedas an indicator to analyze the original design and the optimized modelof the turbine. In the turbine model, there are 12 rotor blades, 17 nozzleblades and 19 optimized nozzle blades. The number of rotor singlepassage grids is 460,000, that of nozzle single passage grids is 200,000,and that of whole flow passage grids is about 8.3 million. The nozzleinlet takes the pressure boundary, the total pressure is 0.393 MPa, andthe total temperature is 345.15 K. The rotor outlet takes the pressureboundary, the pressure is 0.102 MPa, and the working fluid is R123.The rotor flow passage adopts a rotating coordinate system, and therotational speed of the rotor is set to 54,950 r/min, the nozzle flowpassage is a stationary coordinate system. The interface boundary isused to connect the moving area to the static area, and the wall conditionis set to the adiabatic wall condition.The static pressure distribution of the turbine before and after theoptimization is shown in Fig. 19. The cross section at 50% of the bladeheight is selected for observation. The trends of corresponding workingfluid flow before and after optimization are basically the same. Afterthe working fluid passes through the throat of the nozzle blade, thepressure begins to decrease, as shown in Fig. 19(a). There is a highpressure region near the suction surface at the outlet of the nozzleblade, and a small amount of low pressure region is located near thepressure surface, which is consistent with the analysis result of thesingle passage. In the nozzle inlet region, the pressure of the workingfluid is considerably lower than that in the blade. There is a localizedhigh pressure region near the suction surface of the rotor inlet, which isrelated to the shape of the rotor inlet. The optimized turbine flowcharacteristics are superior in Fig. 19(b). The pressure drop gradient ofthe working fluid in the nozzle flow passage is obvious, and the highpressure region of the rotor inlet substantially disappears. The flowcharacteristics of the working fluid have been redistributed, whichimproved the performance of the turbine.The streamline distribution of 50% of the blade height of turbinebefore and after the optimization is shown in Fig. 20. The velocitystreamline of the flow passage in the nozzle is the same, and it issmoother in the flow passage without obvious vortex. At the rotor inlet,there is a small amount of high velocity area, in the velocity streamlineof the working fluid, and the velocity at the pressure surface is relativelyhigher. The velocity of the gas at the rotor outlet is significantlyhigher and there is no remarkable separation. Overall, there is a dramaticalincrease in the velocity of the airflow in the nozzle and rotorflow passage. The nozzle plays a major role in accelerating the workingfluid, and the rotor plays a good guiding role.