Abstract: Aiming at the compressibility of fluid, the flow ripple and method to improve it are studied. The conventional discharge flow formula of a high-pressure vane within vane type pump in fluid drive field power transmission is corrected, which is calculated when the fluid is considered to be incompressible. In order to simulate the actual discharge flow and calculate the uneven coefficient of flow ripple, a mathematic model of theoretical flow is built when the fluid compressibility is considered. Through the study of relationship between working condition parameter and flow ripple of pump, it reveals that the fluid bulk modulus, discharge pressure, rotate speed and the structure of relief grooves are the main influential factors of flow-ripple. The results show that choosing appropriate structure and parameters of relief grooves to make the overall losing flow almost constant can reduce the flow ripple of pump effectively. The overall losing flow is generated by compressed flow, backfilling flow and negative flow due to the thickness of vane.

Key words: Discharge flow, Flow ripple, Uneven coefficient of flow, Vane within vane type pump