In the previous case study of optimum meridian profile of impeller and guidevane, the specific speed was the constant design specification. In this case study, the meridian profiles of optimum specific speed were studied. So, the specific speed is the variable design parameter. The impeller blade number and the guidevane blade number are also the variable design parameters. As the variable design parameters need to change gradually, the blade number is used as real number in the optimum process. In condition of the initial specific speed 1000, initial impeller blade number 2 and initial guidevane blade number 5, the meridian profile of which specific speed has the best efficiency and suction specific speed 1000 was obtained. In condition of the consideration of the only diffusion head loss, the efficiency isn’t affected by impeller outlet normal diameter and rotational speed. In this case study, the loss head of diffusion and the loss head of annular friction are considered. In the process of this optimum study, the 15 variable design parameters were changed constant or variable by two steps. As the result, the best meridian profile of specific speed 785, impeller real blade number 3.4 and guidevane real blade number 14.7 were obtained.

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