# Research on the High Speed of Piston Pumps Based on Rapid Erecting of Launch Vehicles
## 4 Results and Discussion
### Mechanisms for Achieving High Speed of Piston Pumps  
The following is an analysis of the reasons why improved cylinders can achieve high speeds from the perspective of inhibiting cavitation and backflow in the piston chamber. The volume fraction characterises the degree of cavitation development. A higher volume fraction suggests that the region has more serious cavitation. The numerical model takes into account both vaporous cavitation and gaseous cavitation. The vapour volume fraction is used to characterise vaporous cavitation, and the dissolved gas volume fraction is used to characterise gaseous cavitation. The gas phase volume fraction serves to characterise the sum of the two types of cavitation because they both result in a reduced piston chamber filling rate. As shown in Section 4.1, the improved cylinder increases the volumetric efficiency of the piston pump and lowers flow pulsation, which indicates a considerable cavitation suppression effect at speeds exceeding 1500 rpm. In order to explore the gas phase volume fraction in the piston chamber, three sets of conditions were chosen: 2000 rpm, 2500 rpm and 3000 rpm. The analysis is performed when the piston chamber is at 90\({}^{\circ}\), and the lower dead point is at 0\({}^{\circ}\). As shown in Figure 11, when the rotational speed is 2000 rpm, the gas phase volume fraction of the A and B zones of the piston chamber of the modified cylinder block reduces dramatically, and the gas phase volume fraction of the A zone decreases to 0. When the rotational speed is 2500 rpm or 3000 rpm, the gas volume fraction in the A and B zones of the piston chamber of the improved cylinder block does not decrease much due to the rise in centrifugal force, but the gas volume fraction of the entire piston chamber falls. The variation of the gas phase volume fraction in the piston chamber with time for the traditional and improved cylinder blocks under three sets of operating conditions (Figure 12) exhibits that the improved cylinder block effectively suppresses cavitation in the piston chamber. The peak gas phase volume fraction in the piston chamber of the modified block dropped by 3.508%, 9.423% and 6.962%, respectively, at speeds of 2000 rpm, 2500 rpm and 3000 rpm, compared to the traditional block, greatly suppressing cavitation in  
Figure 11: Traditional and improved gas-phase volume fraction cloud map of the piston chamber. the piston chamber. This is due to the increased window area and increasing piston pump discharge flow. While at the same rate of change in volume, the larger overflow surface reduces the suction speed to the critical cavitation speed. Therefore, under high-speed conditions, increasing the window overflow area can effectively inhibit cavitation in the piston pump. The main form of cavitation in the piston pump at high speeds is vaporous cavitation. The magnitude of the vapour volume fraction reflects the degree of vaporous cavitation. The vapour volume fraction curves of both traditional and improved piston chambers are shown in Figure 13. The peak vapour volume fraction of the piston chamber is lowered by 0.492%, 1.498% and 4.250% for 2000 rpm, 2500 rpm and 3000 rpm, respectively, compared to the conventional cylinder block, as shown in the graph. As a result, the improved cylinder can effectively suppress vaporous cavitation in the piston chamber, and the quicker the speed, the better the effect of suppressing vaporous cavitation. The filling rate of the piston chamber is considerably enhanced when the cylinder block is improved, as indicated in Table 2. At 2000 rpm, the piston chamber filling rate before and after improvement is 89.703% and 97.532%, respectively, and the volume efficiency  
Figure 12: Traditional and improved gas-phase volume fraction curve of the piston chamber. Figure 13: Vapour volume fraction curve. is 74.465% and 91.755%. The liquid filling rate and volumetric efficiency of the piston chamber are not identical, owing primarily to backflow.