In this study, a mixed-flow pump with a specified specific speed was optimally designed by utilizing computational fluid dynamics (CFD). Additionally, the shape of the mixed-flow pump and flow characteristics depending on the specific speed were studied, in order to development of hydrodynamic design system for mixed-flow pump. A mixed-flow pump consists of an impeller and a diffuser and the shapes of mixed-flow pumps show a certain tendency depending on specific speed. With an analysis of the shapes of a mixed-flow pump, the optimal shape to satisfy design specifications can easily be designed. The design variables of the impeller and diffuser were defined in meridional plane and vane plane development, and optimum design of the impeller and diffuser was carried out by using design of experiment (DOE). The tendencies of design variables depending on specific speed were analyzed by utilizing the shape of optimally designed mixed-flow pump. The mixed-flow pump shape of required design specification was designed by using the tendencies of design variables depending on specific speed. The performance of designed model has been verified using CFD.
To investigate the internal distribution regularities of shock wave structure in 1+1/2 (without low pressure guide vane) counter-rotating turbine, both steady and unsteady numerical simulation about a designed 1+1/2 counter-rotating turbine are conducted, and experimental research about the shock wave structure of high pressure guide vane, high pressure rotor and low pressure rotor was also conducted by using the schlieren apparatus under different working conditions. The numerical simulation divides into two parts: steady and unsteady calculation. The result of steady simulation under designed condition shows that there appears supersonic flow and shock wave at the exit of root in high pressure guide vane, while supersonic flow appears at the entire passage of the blade outlet in both the high pressure rotor and low pressure rotor, together with strong shock wave and complex wave structures. From the point of the unsteady results, the unsteady effect has few influence on the flow field of high pressure guide vane, but the wake of the high pressure guide leaves periodically sweeps through the front edge of the high pressure blade and there presents strong unsteady effect on flow field of high pressure rotor. Then, to deeply research the characteristics of the shock wave structure, 50% height section of the blade of the three types of blades are extracted respectively to make plane cascades which are conducted blowing experiments in supersonic wind tunnel. During the experiment schlieren display technology is used to record the shock wave structure changing process in three cascade flow passage under the design Angle of attack when pressure ratio changes from 1.7 to 2.5. The final photograph were analyzed by comparing with the CFD results. Results show that with the increase of expansion ratio, the wave structures in both high and low pressure blade channel move toward the exit and the caudal interference between the outer tail wave and is strengthened gradually. The results show that the current design of high pressure blade and low pressure blade show better advantages for controlling the structure of the shock wave.
To improve centrifugal pump cavitation performance, the slot pulse jet pump is proposed. The slot is designed directly on the impeller shroud near the suction side of the blade leading edge. The slots are alternately blocked by the cambered prominence, which is designed at the impeller front side chamber along the circumferential direction. The leakage flow from the front side chamber flows into the slot alternately, and the pulse jet is formed near the blade inlet. Because of the strong shear, the pulse jet is more efficient than steady jet in terms of energy transmission. Based on the numerical simulation, the hydraulic performances of the slot pulse jet pumps with two different pulse frequencies are compared with the slot steady jet pump. The calculation result shows that with the increase of flow rate, the head and efficiency of the three kinds of pumps are basically the same. The cavitation performance of slot pulse jet pump is better than that of slot steady jet pump, especially for slot pulse jet pump II. The distribution of pressure difference acted on the slot appears to be jagged, and the pulse frequency is consistent with shaft frequency or its harmonic frequency. The amplitude of the pressure fluctuation on slot jet pump II is much higher than that of the slot pulse jet pump I. The vapor volume distribution in the middle span of the impeller for slot pulse jet pump is less than that of slot steady jet pump. So, the pulse jet is an effective way to further improve the cavitation performance of slot steady jet pump, and NPSHr is significantly decreased, especially at design condition.