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This article details the construction of an experimental visualization platform for observing cavitation. The platform uses high-speed photography and particle image velocimetry (PIV) techniques to conduct experimental research into the flow pattern and vortex field of cavitation in Venturi tubes. Dynamic mode decomposition is employed to extract the energy distribution characteristics of the cavitation flow field. Cavitation occurs at an exit-to-inlet pressure ratio of 0.595, and the length of the cavitation zone increases as this ratio decreases. When the pressure ratio reaches 0.280, the flow rate remains almost constant and the flow becomes chocked. The cavitation shape evolves periodically in the chocking flow, and the cavitation zone can be divided into three parts: an initiation and development area, a fusion area, and a collapse area. The fusion area exhibits periodic changes in the form of contraction, expansion, and re-contraction. Near the wall, the collapse area exhibits complex boundary conditions, with re-entrant jet causing bubble aggregation, rolling, and shedding. PIV and energy extraction reveal that vortices primarily appear near the wall, where they undergo a periodic process of fragmentation and fusion. The strength of the vortices exhibits a small–large–small pattern that is related to the cloud aggregation, rolling, and shedding caused by the re-entrant jet. [ABSTRACT FROM AUTHOR]

In this study, phenomenological observations and the Kreuer interpretation of the origin of viscosity were used to develop a computational method for solving the turbulence problem of incompressible viscous Newtonian fluids based on extended Navier–Stokes (N–S) equations. The shear process in fluid flow was hypothesized to be accompanied by eddy formation, and the effects of eddies on the convection and diffusion were considered. The classical N–S equations were improved to obtain extended N–S equations. The extended equations are closed, and the sources of the velocity fluctuations are explicitly considered to be additional convection and diffusion. The extended equations are compatible with the classical N–S equations; thus, they can describe laminar and turbulent flows in a unified manner. In fluid flow simulations, the equations describing the mean flow quantities could be directly obtained from the extended N–S equations without any additional turbulence models. A numerical investigation was carried out to verify the extended equations by exploring the flow over a cube placed in a channel. The simulation results were compared with both the large eddy simulation and experimental results. [ABSTRACT FROM AUTHOR]

The magnetic fluid seal (MFS) is a new type of sealing method that offers the advantages of no leakage and low wear. Hence, it is widely used in rotary seals in coal, chemical, and electric power fields. However, at high speeds, the degradation and even failure of the sealing performance severely limits the application of MFS in engineering. Therefore, this study designed a combined sealing device comprising a double screw seal and MFS and optimized the pressure resistance of the screw seal using an orthogonal test in combination with the response surface optimization method. Thus, the pressure resistance could be raised to 3.1 times that before optimization. The effect of the sealing gap on the sealing pressure of the MFS was analyzed by numerical simulation, and an optimal sealing gap value of 0.2 mm was obtained. The results of the verification test showed that the performance of the combined seal was significantly better than that of MFS alone. When sealing liquids, the pressure resistance of the combined seal reached 3.3 times that of the MFS at 3000 rpm, which indicates the application potential of MFS in high-speed working conditions. [ABSTRACT FROM AUTHOR]

Significant breakthroughs in the theory and applications of ferrofluid have broadened their usage in areas such as sealing and actuation. However, the development of numerical ferrofluid dynamics has been slow owing to inadequate multi-field coupling techniques and incomplete equations for turbulence in ferrofluid flow. The understanding of low-Reynolds-number turbulent flow mechanisms in ferrofluid at small scales, particularly in sealing and actuation applications, remains limited, therefore hindering further advancements. This article delves into the turbulent flow equations for general fluid and discusses the influence of different-scale vortices on the average fluid motion. An anisotropic turbulence model was introduced and verified using fluid flow around a cylinder. Magnetic and flow fields data were coupled through node ranking and interpolation methods. By introducing the interaction force of magnetic dipoles, the turbulent equations were refined within Euler grids, thereby establishing a numerical model for the turbulent motion of ferrofluids influenced by multiple fields. This model was applied to study the deformation and migration processes of ferrofluid under an external magnetic field. The variations in ferrofluid motion under magnetic forces were encapsulated, and macroscopic flow comparisons were made through experiments, which demonstrated good consistency. This research provides new methods and ideas for use in ferrofluid numerical studies. Additionally, it offers valuable technical support that can aid in developing industrial products such as sealing and driving devices based on ferrofluids. [ABSTRACT FROM AUTHOR]

The flow and temperature properties of the magnetic fluid are the primary elements impacting the seal stability in the main shaft magnetic fluid seal of the turbine. This study investigated the eddy current and heat field of the magnetic fluid at the seal gap using a mix of numerical computation and experiment and came to the following conclusions: Under the pole tooth groove and the permanent magnet, the magnetic fluid creates symmetrical vortices in the clearance of the magnetic fluid seal device. Below the pole tooth, the magnetic fluid velocity is minimal and essentially constant. The pole shoe and spindle next to the air side of the magnetic fluid seal device have the lowest temperature, and the device's core has the greatest temperature. [ABSTRACT FROM AUTHOR]

The widths and shapes of sealing interfaces are key indicators for characterizing the sealing stability of dynamic and static magnetic fluid seals. In this study, the interface of a magnetic fluid seal was numerically simulated and changes in the interfacial shape and width were tested and verified using a magnetic fluid seal device. The results showed that the pressure resistance decreased with an increase in seal clearance, and the magnetic fluid seal interface generated a small leakage channel. Following the complete formation of the leakage channel, the static seal gradually failed. During failure, the interface width of the magnetic fluid became narrow. At a certain pressure, the maximum pressure resistance decreased as a function of the rotational speed. Compared with a static seal, more small leakage channels and bubbles were generated. In constant conditions, such as fixed sealing clearance speed during dynamic and static sealing, the change in the width of the magnetic fluid interface of the dynamic seal was 5–7 times that of the static seal. [ABSTRACT FROM AUTHOR]

Ferrofluid micropumps have become an important development in the field of micropumps because of their self-sealing, self-lubricating, and integral properties. To further explore the relationship between pumping velocity and pumping period, in this study, an overlapping grid technology is coupled with a model with six degrees of freedom to perform numerical analyses on the inlet- and outlet-velocity pulsation characteristics of a micropump. The results show that the inlet and outlet velocities of the micropump are periodic and region-dependent and are not affected by backpressure and rotating speed. The rotating speed determines the pumping speed of the micropump, and the ratio of the rotating speeds under two working conditions is equal to the ratio of the pumping speeds. In a laminar flow range, where the Reynolds number is 8, the outlet velocity exhibited a small lateral pulsation (of 10−4 orders of magnitude). The backpressure and pumping fluid at the outlet pressurized by the micropump are key factors that induce the backflow of the micropump. To solve the backflow problem, a double-piston micropump structure that is effective in restraining backflow, without requiring additional mechanical devices, and retains the compactness and simplicity of the micropump is proposed. [ABSTRACT FROM AUTHOR]

The rheological mechanisms governing the viscosity characteristics of nano-ferrofluids are very complicated; there is no universal theoretical treatment that explains the dependence of the ferrofluid viscosity on the flow, magnetic, and temperature fields. Thus, determining the viscosity characteristics of ferrofluids in various physical fields is of great theoretical and practical significance. This study explores experimentally the relationship between the ferrofluid viscosity and temperature, magnetic-field strength, and magnetic-field inclination. A special experimental bench on which the magnetic field and temperature can be precisely controlled is designed and constructed. It is found that the ferrofluid viscosity is negatively correlated with temperature. Increasing the percentage of the magnetic particles in the ferrofluid increases the viscosity at any given temperature. Ferrofluids are shown to exhibit the magnetic–viscosity phenomenon: under the action of a magnetic field, the viscosity increases until a magnetic viscosity saturation value is reached. Increasing the magnetic field inclination can aggravate the magnetic–viscosity phenomenon but does not change the saturation value. Contrary to the naïve Hall theory but in agreement with earlier phenomenological studies, the magneto-viscous effect is greater with horizontal than with vertical magnetic fields. Simultaneous exposure to temperature and magnetic fields is investigated; the two fields appear to act independently on the viscosity. The magnetic viscosity saturation value is not affected by temperatures in the range of 30–60 °C. [ABSTRACT FROM AUTHOR]