Analysis and optimal selection of stage velocity ratio and DN-value for micro radial turbine

Based on the expression of the wheel efficiency for radial turbines, the matching relationship between the stage velocity ratio and the reaction degree was analyzed by the analytic method. The influences of the key parameters on the matching results were discussed. Then, the DN-value derived from the stage velocity ratio was analyzed and selected. The results indicate that the stage velocity ratio should match the reaction degree in the design of micro radial turbines, otherwise the higher wheel efficiency can not be obtained. With the different structure of the micro turbine, the optimum range of the stage velocity ratio is 0.64-0.72 for a radial-axial turbine and 0.72-0.80 for a pure radial turbine, respectively. Moreover, the DN-value is relative to structural style, size, design working condition, efficiency, bearing and shafting of the micro radial turbine more directly than the stage velocity ratio. These results imply that the DN-value is a highly concentrated parameter and can be applied in the design of micro radial turbines instead of the stage velocity ratio.