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Register a new userComparison of Analytical and Numerical Models for Point to Ring Electro-Hydrodynamic Flow
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An electrohydrodynamic (EHD) flow in a point-to-ring corona configuration is investigated experimentally, analytically and via a multiphysics numerical model. The interaction between the accelerated ions and the neutral gas molecules is modeled as an external body force in the Navier-Stokes equation (NSE). The gas flow characteristics are solved from conservation principles with spectral methods. The analytical and numerical simulation results are compared against experimental measurements of the cathode voltage, ion concentration, and velocity profiles. A nondimensional parameter, X, is formulated as the ratio of the local electric force to the inertial term in the NSE. In the region of X > 1, the electric force dominates the flow dynamics, while in the X << 1 region, the balance of viscous and inertial terms yields traditional pipe flow characteristics.
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Electrohydrodynamic (EHD) flow induced by planar corona discharge in the wall boundary layer region is investigated experimentally and via a multiphysics computational model. The EHD phenomena has many potential engineering applications, its optimization requires a mechanistic understanding of the ion and flow transport. The corona EHD actuator consisting of two electrodes located in the wall boundary layer creates an EHD driven wall jet. The applied voltage between the electrodes is varied and the resulting effects in the charge density and flow field are measured. Constant current hotwire anemometry is used to measure velocity profile. The airflow near the wall acts a jet and it reaches a maximum of 1.7 m/s with an energy conversion efficiency of ~2%. The velocity decreases sharply in the normal direction. Multiphysics numerical model couples ion transport equation and the Navier Stokes equations to solve for the spatiotemporal distribution of electric field, charge density and flow field. The numerical results match experimental data shedding new insights into mass, charge and momentum transport phenomena. The EHD driven flow can be applied to flow control strategies and design of novel particle collectors.
The study focuses on the 3D electro-hydrodynamic (EHD) instability for flow between to parallel electrodes with unipolar charge injection with and without cross-flow. Lattice Boltzmann Method (LBM) with two-relaxation time (TRT) model is used to study flow pattern. In the absence of cross-flow, the base-state solution is hydrostatic, and the electric field is one-dimensional. With strong charge injection and high electrical Rayleigh number, the system exhibits electro-convective vortices. Disturbed by different perturbation patterns, such as rolling pattern, square pattern, and hexagon pattern, the flow patterns develop according to the most unstable modes. The growth rate and the unstable modes are examined using dynamic mode decomposition (DMD) of the transient numerical solutions. The interactions between the applied Couette and Poiseuille cross-flows and electroconvective vortices lead to the flow patterns change. When the cross-flow velocity is greater than a threshold value, the spanwise structures are suppressed; however, the cross-flow does not affect the streamwise patterns. The dynamics of the transition is analyzed by DMD. Hysteresis in the 3D to 2D transition is characterized by the non-dimensional parameter Y, a ratio of the coulombic force to viscous term in the momentum equation. The change from 3D to 2D structures enhances the convection marked by a significant increase in the electric Nusselt number.
In a cylindrical container filled with an eutectic GaInSn alloy, an electro-vortex flow (EVF) is generated by the interaction of a non-uniform current with its own magnetic field. In this paper, we investigate the EVF phenomenon numerically and experimentally. Ultrasound Doppler Velocimetry (UDV) is applied to measure the velocity field in a cylindrical vessel. Second, we enhance an old numerical solver by taking into account the effect of Joule heating, and employ it for the numerical simulation of the EVF experiment. Special focus is laid on the role of the magnetic field, which is the combination of the current induced magnetic field and the external geomagnetic field. For getting a higher computational efficiency, the so-called parent-child mesh technique is applied in OpenFOAM when computing the electric potential, the current density and the temperature in the coupled solid-liquid conductor system. The results of the experiment are in good agreement with those of the simulation. This study may help to identify the factors that are essential for the EVF phenomenon, and for quantifying its role in liquid metal batteries.
Spark plasma discharges induce vortex rings and a hot gas kernel. We develop a model to describe the late stage of the spark induced flow and the role of the vortex rings in the entrainment of cold ambient gas and the cooling of the hot gas kernel. The model is tested in a plasma-induced flow, using density and velocity measurements obtained from simultaneous stereoscopic particle image velocimetry (S-PIV) and background oriented schlieren (BOS). We show that the spatial distribution of the hot kernel follows the motion of the vortex rings, whose radial expansion increases with the electrical energy deposited during the spark discharge. The vortex ring cooling model establishes that entrainment in the convective cooling regime is induced by the vortex rings and governs the cooling of the hot gas kernel, and the rate of cooling increases with the electrical energy deposited during the spark discharge.
Modification and control over the vaporization kinetics of microfluidic droplets may have strong utilitarian implications in several scientific and technological applications. The article reports the control over the vaporization kinetics of pendent droplets under the influence of competing internal electrohydrodynamic and ferrohydrodynamic advection. Experimental and theoretical studies are performed and the morphing of vaporization kinetics of electrically conducting and paramagnetic fluid droplets using orthogonal electric and magnetic stimuli is established. Analysis of the observations reveals that the electric field has a domineering influence compared to the magnetic field. While the magnetic field is noted to aid the vaporization rates, the electric field is observed to decelerate the same. Neither the vapour diffusion dominated kinetics nor the field induced modified surface tension can explain the observed vaporization behaviours. Velocimetry within the droplet shows largely modified internal ferro and electrohydrodynamic advection, which is noted to be the crux of the mechanism towards modified vaporization rates. A mathematical treatment is proposed and takes into account the roles played by the governing Hartmann, electrohydrodynamic, interaction, the thermal and solutal Marangoni, and the electro and magneto Prandtl and Schmidt numbers. It is observed that the morphing of the thermal and solutal Marangoni numbers by the electromagnetic interaction number plays the dominant role towards morphing the advection dynamics. The model is able to predict the internal advection velocities accurately. The findings may hold significant promise towards smart control and tuning of vaporization kinetics in microhydrodynamics transport paradigms.
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