By using a pressure-based method and the finite volume method in the framework of the time dependent Reynolds-averaged Navier-Stokes equations, the authors studied the unsteady process of ventilated cavities generated...By using a pressure-based method and the finite volume method in the framework of the time dependent Reynolds-averaged Navier-Stokes equations, the authors studied the unsteady process of ventilated cavities generated forcing air through an orifice in a 2D hydrofoil without natural cavitation physically. The computation was carried out with the Volume Of Fluid （VOF） technique to track the gas-liquid two-phase interface. The results of simulation indicate that the ventilation rate is an important parameter in determining the morphology of cavity. There exists a critical value to convert sheet cavity into supereavity. A high ventilation rate can induce a two phase interface fluctuation and enable the ventilated eavitating flow to present a characteristic of periodicity.展开更多
The fluctuation law of magnetic fluid seal interface of an agricultural centrifugal pump is theoretically unknown;the pressure and velocity fluctuations are crucial factors that cause interface fluctuation.In this stu...The fluctuation law of magnetic fluid seal interface of an agricultural centrifugal pump is theoretically unknown;the pressure and velocity fluctuations are crucial factors that cause interface fluctuation.In this study,the pressure and velocity fluctuations of the sealing interface on an agricultural centrifugal pump during cavitation were investigated based on the methods of Ansys CFX numerical calculation and experimental verification.The results demonstrated that at the same flow rate,the pressure fluctuation amplitude of the sealing interface decreased gradually from the shaft surface to the bottom of the polar tooth.At different flow rates,the amplitude of the pressure fluctuation decreased with an increase in the flow rate.The cavitation of the medium aggravated the impact and water hammer of the liquid,leading to the occurrence of the jitter phenomenon in the sealing interface to accelerate the fluctuation frequency of the axial velocity of the sealing liquid,which accelerated the emulsification of the magnetic fluid.This law can provide a reference for the design of magnetic fluid sealing devices for agricultural centrifugal pumps.展开更多
The scale analysis of the layered flow problem of the shallow sea shows that the parameter of E V represented the relative thickness of the friction layer is the little value larger than Rossby number. This illustrat...The scale analysis of the layered flow problem of the shallow sea shows that the parameter of E V represented the relative thickness of the friction layer is the little value larger than Rossby number. This illustrates that they are not ignorable and the important control factors of the layered flow although friction effect is only limited within interface Ekman layer and bottom Ekman layer. Using larger little parameter E V as the little perturbation parameter is more reasonable than using the classical Rossby number ε. By using the perturbation expansion and doing the researches of the structure of the Ekman layer on the sea surface, sea bottom and interface, a group of new layered flow vorticity equation is derived. It combines the vorticity of the flow of every layer, the inclination of the interface, the inclination of the sea bottom and the wind stress vorticity on the sea surface. Different from the conventional vorticity equation, which derived by using Rossby number as little parameter and is applied to large scale motion, it allows relatively large interfaces fluctuation, even it is applied to the problem that interface touch the bottom or touch the sea surface.展开更多
To better analyzing the temperature oscillation and the two-phase behavior inside a flat loop heat pipe,visual studies were conducted.Under the 20℃ water cooling and horizontal orientation,the effects of the filling ...To better analyzing the temperature oscillation and the two-phase behavior inside a flat loop heat pipe,visual studies were conducted.Under the 20℃ water cooling and horizontal orientation,the effects of the filling ratio and heat loads on the temperature oscillation were analyzed.Based on the experimental data,the results indicate that owing to the increased system pressure,the temperature oscillation decays as the filling ratio increases from 34%to 58%.Meanwhile,during the startup process,temperature oscillation tends to occur during the boiling and steady stages due to the more violent two-phase behavior,while the temperature curves are smooth during the slow evaporation stage.Moreover,as the heat load increases,the evaporation becomes more intense at the active zone of evaporator,leading to a faster startup process and a higher oscillation frequency.Besides,owing to the synergistic effect of two-phase flow in the compensation chamber caused by heat leak and subcooled liquid backflowing,a“breathing”oscillation behavior of the vapor-liquid interface is observed at the compensation chamber,which further leads to the unstable operation behavior of the loop heat pipe system.展开更多
文摘By using a pressure-based method and the finite volume method in the framework of the time dependent Reynolds-averaged Navier-Stokes equations, the authors studied the unsteady process of ventilated cavities generated forcing air through an orifice in a 2D hydrofoil without natural cavitation physically. The computation was carried out with the Volume Of Fluid （VOF） technique to track the gas-liquid two-phase interface. The results of simulation indicate that the ventilation rate is an important parameter in determining the morphology of cavity. There exists a critical value to convert sheet cavity into supereavity. A high ventilation rate can induce a two phase interface fluctuation and enable the ventilated eavitating flow to present a characteristic of periodicity.
基金support of the National Natural Science Foundation of China(Grant No.52079118)the Science and Technology Department of Sichuan Province(Grant No.2020YFH0135)+2 种基金the Open Research Subject of Key Laboratory of Fluid and Power Machinery(Xihua University)Ministry of Education(Grant No.LTDL2021-005)Project of Science and Technology Department of Sichuan Province,(Grant No.202573).
文摘The fluctuation law of magnetic fluid seal interface of an agricultural centrifugal pump is theoretically unknown;the pressure and velocity fluctuations are crucial factors that cause interface fluctuation.In this study,the pressure and velocity fluctuations of the sealing interface on an agricultural centrifugal pump during cavitation were investigated based on the methods of Ansys CFX numerical calculation and experimental verification.The results demonstrated that at the same flow rate,the pressure fluctuation amplitude of the sealing interface decreased gradually from the shaft surface to the bottom of the polar tooth.At different flow rates,the amplitude of the pressure fluctuation decreased with an increase in the flow rate.The cavitation of the medium aggravated the impact and water hammer of the liquid,leading to the occurrence of the jitter phenomenon in the sealing interface to accelerate the fluctuation frequency of the axial velocity of the sealing liquid,which accelerated the emulsification of the magnetic fluid.This law can provide a reference for the design of magnetic fluid sealing devices for agricultural centrifugal pumps.
文摘The scale analysis of the layered flow problem of the shallow sea shows that the parameter of E V represented the relative thickness of the friction layer is the little value larger than Rossby number. This illustrates that they are not ignorable and the important control factors of the layered flow although friction effect is only limited within interface Ekman layer and bottom Ekman layer. Using larger little parameter E V as the little perturbation parameter is more reasonable than using the classical Rossby number ε. By using the perturbation expansion and doing the researches of the structure of the Ekman layer on the sea surface, sea bottom and interface, a group of new layered flow vorticity equation is derived. It combines the vorticity of the flow of every layer, the inclination of the interface, the inclination of the sea bottom and the wind stress vorticity on the sea surface. Different from the conventional vorticity equation, which derived by using Rossby number as little parameter and is applied to large scale motion, it allows relatively large interfaces fluctuation, even it is applied to the problem that interface touch the bottom or touch the sea surface.
基金This work was supported by National Natural Science Foundation of China(NSFC)(Grant No.51878254)National Key R&D Program of China(Grant No.2018YFE0111200)+1 种基金Key Research and Development Plan of Hunan Province(2020WK2012)Hunan Provincial Science and Technology Department(2020GK4057).
文摘To better analyzing the temperature oscillation and the two-phase behavior inside a flat loop heat pipe,visual studies were conducted.Under the 20℃ water cooling and horizontal orientation,the effects of the filling ratio and heat loads on the temperature oscillation were analyzed.Based on the experimental data,the results indicate that owing to the increased system pressure,the temperature oscillation decays as the filling ratio increases from 34%to 58%.Meanwhile,during the startup process,temperature oscillation tends to occur during the boiling and steady stages due to the more violent two-phase behavior,while the temperature curves are smooth during the slow evaporation stage.Moreover,as the heat load increases,the evaporation becomes more intense at the active zone of evaporator,leading to a faster startup process and a higher oscillation frequency.Besides,owing to the synergistic effect of two-phase flow in the compensation chamber caused by heat leak and subcooled liquid backflowing,a“breathing”oscillation behavior of the vapor-liquid interface is observed at the compensation chamber,which further leads to the unstable operation behavior of the loop heat pipe system.
