Case Study of Tandem Impeller Rotating at Different Speeds

In previous study, the optimum meridian profile of tandem impeller rotating at the same speed was obtained by means of calculation of efficiency and suction specific speed considering two diffusion factors of tandem impeller. The effect of theoretical head ratio between the first impeller and the second impeller was obtained. In this study, the optimum meridian profile and design parameters of tandem impeller rotating at two kinds of different speed was obtained. In the process of this study, a lot of design parameters were needed. Therefore, in the optimum calculation process the predominant design parameters of two impellers were selected and re-selected. The predominant design parameters were inlet relative flow angle, turning angle, meridian velocity ratio, inlet and outlet diameter ratio and so on. The impeller meridian velocity ratios of shape factors were defined as k_c12(= C_m2/C_m1) and k_cp2(= C_m2/C_mp), and the impeller diameter ratios were defined as k_d12(= D_1c/D_2c) and k_dp2(= D_pc/D_2c). The subscripts 1,p and 2 means the first impeller inlet, the second impeller inlet and the second impeller outlet respectively. And theoretical head ratio between first impeller and second impeller was defined as k_Hth(= H_tha/H_thb). The rotational ratio between the first impeller and the second impeller defined as R_na(= n_a/n_b). The Optimum R_na(= n_a/n_b) was effected by the other design parameter. As the result, the optimum meridian profile of tandem impeller rotating at different speeds was obtained. This method can be also used for the suitable rotative guidevane.