Abstract:The regime of compressible flow generally refers to the super/subsonic case. However, several remarkable cases with low Mach number could not be appropriately described with the incompressible method. It is a similar case for a cavitating jet inside a poppet valve. In order to comprehensively address the discrepancy between incompressible and compressible methods, both non-cavitating and cavitating cases are performed in experiment and calculation based on OpenFOAM. Experiment reveals a transition in flow patt… Show more
“…Due to throttling loss, the pressure drops sharply at the recovery valve, when the pressure drops to the saturated vapor pressure of the oil, gas will be released from the oil around the recovery valve. Because the oil is mixed with large bubbles, resulting in the oil presents a non-contact state, this phenomenon is known as the hydraulic shock absorber cavitation phenomenon (Yuan, Song, & Liu, 2019).…”
Section: Mechanism Of Cavitation Phenomenonmentioning
To prevent the occurrence of the cavitation phenomenon in hydraulic shock absorber, the production process of the cavitation during the recovery process of shock absorber is studied, and the parameter model of cavitation production mechanism is built. Based on Computational Fluid Dynamics (CFD) numerical method, a high-precision mesh model of shock absorber is established and the simulation analysis is carried out by using FLUENT software. Therefore, the specific position and distribution of cavitation in the hydraulic shock absorber are obtained, and the measures to inhibit cavitation are put forward. Finally, the simulation results are verified by experimental study and the experimental results show that the cavitation is mainly distributed around the recovery valve of shock absorber, and the cavitation phenomenon becomes more obvious with increasing the piston speed; using low viscosity oil and increasing the diameter of piston rod can effectively inhibit cavitation phenomenon. This study provides a certain reference for preventing the cavitation phenomenon of hydraulic shock absorber.
ARTICLE HISTORY
“…Due to throttling loss, the pressure drops sharply at the recovery valve, when the pressure drops to the saturated vapor pressure of the oil, gas will be released from the oil around the recovery valve. Because the oil is mixed with large bubbles, resulting in the oil presents a non-contact state, this phenomenon is known as the hydraulic shock absorber cavitation phenomenon (Yuan, Song, & Liu, 2019).…”
Section: Mechanism Of Cavitation Phenomenonmentioning
To prevent the occurrence of the cavitation phenomenon in hydraulic shock absorber, the production process of the cavitation during the recovery process of shock absorber is studied, and the parameter model of cavitation production mechanism is built. Based on Computational Fluid Dynamics (CFD) numerical method, a high-precision mesh model of shock absorber is established and the simulation analysis is carried out by using FLUENT software. Therefore, the specific position and distribution of cavitation in the hydraulic shock absorber are obtained, and the measures to inhibit cavitation are put forward. Finally, the simulation results are verified by experimental study and the experimental results show that the cavitation is mainly distributed around the recovery valve of shock absorber, and the cavitation phenomenon becomes more obvious with increasing the piston speed; using low viscosity oil and increasing the diameter of piston rod can effectively inhibit cavitation phenomenon. This study provides a certain reference for preventing the cavitation phenomenon of hydraulic shock absorber.
ARTICLE HISTORY
“…Furthermore, the computational fluid dynamics (CFD) technology has been increasingly used in the research of the multiphase pumps, valves or other multiphase flows (Hao & Tan, 2018;Yuan et al, 2019). And the CFD reliability has been confirmed by the comparisons with experimental tests (Ramezanizadeh et al, 2019;Yu et al, 2015Yu et al, , 2019.…”
Instantaneous gas-liquid flow and distribution have an important influence on the performance of a multiphase pump, especially under the high gas content conditions. How to accurately simulate the complete working cycle of a multiphase pump and reflect the transient oil-gas flow inside the pump cavity are the main difficulties of the study. A three-dimensional whole-cycle numerical simulation has been conducted to predict the void fraction waves of the reciprocating multiphase pumps under the high gas rates and to evaluate the effects of multi-case parameters on its pulsation characteristics. The instantaneous two-phase distribution and fluctuation characteristic accompanying the movement of the piston and the valves during each process of the multiphase pump are innovatively obtained under the high gas rates. Five different ideal gas model and real gas models used in this simulation are compared and optimized first, and then validated by the experimental results. Void fraction wave signals in the time and frequency domains are obtained from multiple working cycles of the multiphase pump, and the pulsation rates, propagation speeds, amplitudes, and power spectral densities are analyzed in great detail under different inlet gas contents, pressure ratios, crank speeds, and stroke lengths.
“…Previous experimental evidence (Kumagai et al, 2016) indicated that an intimate interrelationship exists between the periodic behavior of the cavitating bubbles and the induced pressure fluctuation inside a poppet valve, but the underlying mechanisms associated with the microscopic flow dynamics have not been thoroughly clarified. Notably, an earlier study on numerical methods for a transitional cavitating jet (Yuan et al, 2019b) motivated a two-dimensional transient simulation of the cavitating jet inside an oil poppet valve, which revealed the complicated correlation between cavitation evolution and flow performance. However, owing to the much smaller viscosity of water fluid, the unsteady behavior of a water cavitating jet may display a substantial difference from that of an oil cavitating jet, and simulation of the water cavitating jet requires both an elaborate numerical treatment and significantly more computational resources to resolve the small-scale vortex cavitation structure featured with both three-dimensionality and highly transient characteristics.…”
Owing to the strong three-dimensionality and transient evolution, the flow dynamics of a cavitating jet inside a water poppet valve is poorly understood, leading to insufficient basis for exploring the governing mechanism of cavitation effects. In this paper, a three-dimensional simulation considering the compressibility of each constituent phase is performed, to clarify the governing mechanisms under the cavitating flow inside two water poppet valves. The cavitation structures inside the poppet valves are primarily located at three regions and triggered by different mechanisms. The vortex cavitation, mainly confined within the free shearing layer, is due to vortex dynamics, while the attached cavitation at the poppet trailing edge and within the chamfered groove arises from flow separation. The fast laminar-turbulent transition process contributes to the three-dimensionality within the free shearing layer and the rear part of the chamfered groove. The flow separation due to the chamfered groove leads to increased velocity of the central potential core, contributing to a different flow discharge performance from that of the poppet valves with a sharp seat. In addition, the periodic variation in cavitation reveals the significant interaction between the shed cavitating vortex and attached cavitation at the poppet trailing edge. In conclusion, the change in velocity distribution due to different poppet valve seat structures leads to variation in flow discharge performance, and the vortex dynamics makes sense for all three kinds of cavitation occurring inside poppet valves.
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