微型向心透平级速比与DN值的最优选择

Analysis and Optimal Selection of Stage Velocity Ratio and DN-Value for Micro Radial Turbine

基于向心透平轮周效率的表达式,利用解析法分析了微型向心透平级速比和反动度的匹配关系,研究了关键参数变化对匹配结果的影响,对从级速比派生出的叶轮进口直径与转速的乘积值（DN值）这一参数进行了选取分析.结果表明：在向心透平设计时,级速比必须与反动度进行匹配选择,单纯选择级速比不能使向心透平具有较高的轮周效率;对于不同的微型向心透平叶轮结构,级速比选取范围不同,径向-轴流式为0.64-0.72,纯径向式为0.72-0.80,级速比为0.72可作为这两种叶轮结构形式选择时的分界点;叶轮DN值能直接反映出叶轮材料、结构形式、设计工况、叶轮尺寸以及轴承轴系等因素,这些因素直接关系向心透平能否实现微型化,因此叶轮DN值是一个高度集中的参数,在微型向心透平设计中可替代级速比.

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.