Some features of cavitation. Throttles are widely used in hydraulic components and hydraulic systems. Therefore, cavitation is also widely present in various hydraulic systems. Cavitation phenomenon itself has some inherent characteristics. By studying these characteristics, not only can we further understand the nature of cavitation phenomenon, but also can give a method to eliminate cavitation phenomenon. When cavitation occurs, it has the following characteristics: (1) After cavitation occurs, although the pressure difference before and after the orifice continues to increase, the flow through the orifice no longer increases. This feature can be called the “occlusion” feature of cavitation. The reason for this characteristic is that the increased pressure difference is consumed in the vaporization zone caused by cavitation. (2) The geometry of the inlet of the throttle position has a considerable influence on cavitation. After cavitation occurs in the orifice with no rounded transition at the entrance, the “bubble curtain” generated by the cavitation is congested in the orifice, causing the orifice to be blocked, which has a significant impact on the flow characteristics. The “bubble curtain” produced by the orifice with rounded transition at the entrance mostly occurs behind the orifice, which has a relatively small impact on the flow characteristics. Therefore, air pockets are more sensitive to the microstructure at the entrance of the orifice and in the orifice. (3) When cavitation occurs, it is accompanied by loud noises, which sounds like “hushing” screams. After testing, it is found that this is caused by the generation and collapse of bubbles in the air pockets. At the same time, high-frequency pulsation occurs in oil pressure, and the frequency of the pulsation is above 200 Hz. If this pulsation is coupled with the natural frequency of other components, it may cause high-frequency pulsation in the hydraulic system.
The effect of cavitation on the operating characteristics of the engine. Cavitation in the process of start-up acceleration By analyzing the start-up and acceleration process of the turbojet engine fuel supply adjustment system, it can be seen that when the regulator valve is opened, the pump outlet pressure has basically risen to the rated pressure. At this time, the fuel regulating valve has not been opened yet, and the restrictor alone supplies fuel to the combustion chamber. Because the pump outlet pressure p rises quickly and the fuel pressure p increases relatively late for a period of time, the pressure difference before and after the restrictor is very large. Comparing the flow characteristics of the restrictor, it can be seen that cavitation occurs in the restrictor at this time, and this period of time lasts about 4s. As the fuel regulating valve opens, the fuel pressure rises rapidly, and when it reaches the second half of the acceleration stage and the cruise state, The pressure difference before and after the restrictor is reduced, and the cavitation phenomenon disappears. Therefore, in the acceleration section, cavitation occurs in the restrictor and lasts for about 4 seconds, which will definitely have a certain impact on the normal operation of the fuel supply regulation system.
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