Study on the Vortex in a Pump Sump and Its Influence on the Pump Unit

The vortex in a pump sump is a negative problem for the pump unit, which can lead to the decline of pump performance. Focusing on the internal pressure characteristics of the floor-attached vortex (FAV) and its influence on the pump unit, the FAV was analyzed adopting the previously verified numerical simulation method and experiment. The results show that the pressure in the vortex core gradually decreases with time, drops to a negative pressure at the development stage, and then reaches the lowest pressure during the continuance stage. When the negative pressure of the vortex tube is around the vaporization pressure of the continuance stage, it can cause a local cavitation at the impeller inlet. The evolution of the FAV is accompanied by a change of pressure gradient in the vortex core which is discussed in detail. This research provides theoretical guidance for a better understanding of the vortex characteristics and the optimal design for the pump.

Vortex Dynamics Analysis of Internal Flow Field of Mixed-Flow Pump under Alford Effect

A multi-region dynamic slip method was established to study the internal flow characteristics of the mixed-flow pump under the Alford effect. The ANSYS Fluent software and the standard k-ε two-equation model were used to numerically predict the mixed-flow pump’s external characteristics and analyze the forces on the impeller and guide vane internal vortex structure and non-uniform tip gap of the mixed-flow pump at different eccentric distances. The research results show that the external characteristic results of the numerical calculation are consistent with the experimental measurement. The head error of the design flow operating point is about 5%, and the efficiency error is no more than 3%, indicating the high accuracy of numerical calculation. Eccentricity has a significant influence on the flow field in the tip area of the mixed-flow pump impeller, the distribution of vortex core in the impeller presents obvious asymmetry, the strength and distribution area of the vortex core in the small gap area of the tip increase obviously, which aggravates the flow instability and increases the energy loss. With the increase of eccentricity, the strength and number of vortex core structures in the guide vane also increase significantly, and obvious flow separation occurs near the inlet of the guide vane suction surface on the eccentric side of the impeller. The circumferential distribution of L1 and L2 values represents the friction pressure gap in the eccentric state, and the eccentricity has a more noticeable effect on L1 and L2 values at the small gap; With the increase of eccentricity, the values of vorticity moment components L1 and L2 increase, and the Alford moment on the impeller increases. The leading-edge region of the blade is the main part affected by the unstable torque of the flow field. With the increase of eccentricity, the impact degree of tip leakage flow deepens, and the change of the tip surface pressure is the most obvious. The impact area of tip leakage flow is mainly concentrated in the first half of the impeller channel, which has an impact on the blade inlet flow field but has little impact on the blade outlet flow field.

Quantifying the quality of optical vortices by evaluating their intensity distributions

Optical vortices are widely used in optics and photonics, ranging from microscopy and communications to astronomy. However, little work has been done to quantify the quality of scalar optical vortices. Since the quality of an optical vortex affects measurements and conclusions derived from their use, development of tools to evaluate the vortex quality is crucial. Moreover, the quality of a vortex strongly depends on the application. Therefore, this work aims to establish metrics for the evaluation of optical vortex quality. We propose to evaluate vortex quality using the following intensity parameters: eccentricity of the intensity distribution, cross-sectional peak-to-valley measurements, cross-sectional peak difference, and the ratio of the ring width to the vortex core diameter (doughnut-ratio). These parameters can be used as a guide for the quality of optical vortices depending on their implementation for specific optical technologies.

The flow topology transition of liquid–liquid Taylor flows in square microchannels

This work investigates the change of the flow topology of Taylor flow and qualitatively relates it to the excess velocity. Ensemble-averaged 3D2C-$$\upmu$$ μ PIV measurements simultaneously resolve the flow field inside and outside the droplets of a liquid–liquid Taylor flow that moves through a rectangular horizontal microchannel. While maintaining a constant Capillary number Ca = 0.005, the Reynolds number ($$0.52 \le {\text{Re}} \le 2.14$$ 0.52 ≤ Re ≤ 2.14 ), the viscosity ratio ($$0.24 \le \lambda \le 2.67$$ 0.24 ≤ λ ≤ 2.67 ) and surfactant concentrations of sodium dodecyl sulfate (0–3 CMC) are varied. We experimentally identified the product of the Reynolds number Re and the viscosity ratio $$\lambda$$ λ to indicate the momentum transport from the continuous phase (slugs) into the droplets (plugs). The position and size of the droplet’s main vortex core as well as the flow topology in the cross section of this vortex core changed with increased momentum transfer. Further, we found that the relative velocity of the Taylor droplet correlates negatively with the evoked topology change. A correlation is proposed to describe the effect quantitatively. Graphical abstract

The unsteady swirling jet in a model of radial burner

The experimental study of an isothermal swirl flow with the formation of a precessing vortex core in the radial swirler upon non-confinement and confinement conditions is carried out. Velocity profiles are obtained with varying Re and guide vane angle, changing the swirl number S. Four acoustic sensors and LDA system are used to measure Strouhal number as the function of the integral swirl number in the range from 0.5 <S <0.8. It is shown that the unsteady flow with PVC effect significantly changes upon non-confinement and confinement conditions.

Nanocavity-Mediated Fast Magnetic Vortex Core In-Situ Switching by Local Magnetic Field

Fast in situ switching of magnetic vortex core in a ferromagnetic nanodisk assisted by a nanocavity, with diameter comparable to the dimension of a vortex core, is systematically investigated by changing the strength as well as the diameter of the effective circular region of the applied magnetic field. By applying a local magnetic field within a small area at the nanodisk center, fast switching time of about 35 ps is achieved with relatively low field strength (70 mT) which is beneficial for fast data reading and writing. The reason for this phenomenon is that the magnetic spins around the nanocavity is aligned along the cavity wall due to the shape anisotropy when the perpendicular field is applied, which deepens the dip around the vortex core, and thus facilitates the vortex core switching.

Observation of frequency dependent resonances in magnetic vortex core gyration using time-resolved magneto-optical Kerr microscope with pulsed semiconductor laser illumination

Frequency dependent resonance of magnetic vortex core gyration in micrometer sized permalloy squares was observed by time-resolved magneto-optical Kerr microscope using pulsed semiconductor lasers as a light source in stroboscopic method. Uniform and efficient laser illumination was realized by a speckle reducer consisting of an oscillating multimode optical fiber and a microbending mode scrambler. The resonance frequency of the same sized permalloy squares showed a non-uniformity of up to 15%, suggesting the flatness of the underlayer have a strong influence to the gyration motion.