Suppression of Flow Separation Around A Circular Cylinder by Utilizing Lorentz Force

Both experimental and numerical investigations on the flow past a cylinder under the influence of Lorentz force （electromagnetic force） were conducted in an electrically low-conducting fluid. The Lorentz force is applied beth locally, wholly and periodically on the surface of the cylinder, and their control effects for flow ,separation were investigated Both experimental and numerical results show that Lorentz force can suppress the flow separation with Lorentz force applied on beth local and whole surface of the cylinder. However, when the periodic and opposite Lorentz force adopted, the cylinder wake cannot be stabilized.

Lorentz force electrical impedance tomography using pulse compression technique

Lorentz force electrical impedance tomography （LFEIT） combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that：（i） LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely; （ii） LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB; （iii） axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.

Influences of Lorentz force on the hydrofoil lift

In this paper, Lorentz forces are proved to be able to suppress separation in flows over hydrofoils. Furthermore, a differential equation of pressure distributions on the hydrofoil surface is derived, from which it is found that BVF （boundary vortex flux） σ is a suitable criterion for describing the lift coefficient variations during the electromagnetic control process. According to our numerical results, the periodic variations of lift for a hydrofoil at an attack angle of 17 ° are analyzed and its inherent mechanism is discussed in detail with the concept of BVE On the other hand, the effects of Lorentz force on the hydrofoil＇s lift are investigated both experimentally and numerically for different magnitudes and locations.

Experimental Research on the Mechanism of Lift Amplification and Vibration Suppression of Lorentz Force

The Lorentz force generated by electromagnetic field on the surface of the cylinder in the electrolyte solution may modify the structure of the flow boundary layer effectively. The transient control process of Lorentz force is investigated experimentally for lift amplification and vibration suppression. The experiments are conducted in a rotating annular tank filled with a low-conducting electrolyte. A cylinder with an electro-magnetic actuator is placed into the electrolyte. The lift force of cylinder is measured using the strain gages attached to a fixed beam, and the flow fields are visualized by the dye markers. The results show that the upper vortex on the cylinder is suppressed, and the wake becomes a line and leans to the lower side under the action of upside Lorentz force while the lower vortex on the cylinder is suppressed and limited in a small region. Therefore, the value of lift increases with the variation of flow field. However, the vortexes on the cylinder are suppressed fully under the action of symmetrical Lorentz force which leads to the suppression of lift oscillation and then the vibration of cylinder are suppressed fully.

Mechanism of controlling turbulent channel flow with the effect of spanwise Lorentz force distribution

A direct numerical simulation（DNS） is performed to investigate the control effect and mechanism of turbulent channel flow with the distribution of spanwise Lorentz force. A sinusoidal distribution of constant spanwise Lorentz force is selected, of which the control effects, such as flow characters, mean Reynolds stress, and drag reductions, at different parameters of amplitude A and wave number k_x are discussed. The results indicate that the control effects vary with the parameter A and k_x. With the increase of A, the drag reduction rate D_r first increases and then decreases rapidly at low k_x,and slowly at high k_x. The low drag reduction（or even drag increase） is due to a weak suppression or even the enhancements of the random velocity fluctuation and mean Reynolds stress. The efficient drag reduction is due to the quasi-streamwise vortex structure induced by Lorentz force, which contributes to suppressing the random velocity fluctuation and mean Reynolds stress, and the negative vorticity improves the distribution of streamwise velocity. Therefore, the optimal control effect with a drag reduction of up to 58% can be obtained.

Mechanism of drag reduction by spanwise oscillating Lorentz force in turbulent channel flow

Numerical simulations and experimental research are both carried out to investigate the controlled effect of spanwise oscillating Lorentz force on a turbulent channel flow. The variations of the streaks and the skin friction drag are obtained through the PIV system and the drag measurement system, respectively. The flow field in the near-wall region is shown through direct numerical simulations utilizing spectral method. The experimental results are consistent with the numerical simulation results qualitatively, and both the results indicate that the streaks are tilted into the spanwise direction and the drag reduction utilizing spanwise oscillating Lorentz forces can be realized. The numerical simulation results reveal more detail of the drag reduction mechanism which can be explained, since the spanwise vorticity generated from the interaction between the induced Stokes layer and intrinsic turbulent flow in the near-wall region can make the longitudinal vortices tilt and oscillate, and leads to turbulence suppression and drag reduction.

Classical Gravitational Interactions and Gravitational Lorentz Force

In quantum gauge theory of gravity, the gravitational field is represented by gravitational gauge field.The field strength of gravitational gauge field has both gravitoelectric component and gravitomagnetic component. In classical level, gauge theory of gravity gives classical Newtonian gravitational interactions in a relativistic form. Besides,it gives gravitational Lorentz force, which is the gravitational force on a moving object in gravitomagnetic field The direction of gravitational Lorentz force is not the same as that of classical gravitational Newtonian force. Effects of gravitational Lorentz force should be detectable, and these effects can be used to discriminate gravitomagnetic field from ordinary electromagnetic magnetic field.

Numerical investigation of turbulent channel flow controlled by spatially oscillating spanwise Lorentz force

A formulation of the skin-friction drag related to the Reynolds shear stress in a turbulent channel flow is derived. A direct numerical simulation （DNS） of the turbulent control is performed by imposing the spatially oscillating spanwise Lorentz force. Under the action of the Lorentz force with several proper control parameters, only the periodi- cally well-organized streamwise vortices are finally observed in the near-wall region. The Reynolds shear stress decreases dramatically, especially in the near-wall area, resulting in a drag reduction.

Improving Residence Time Distribution in Glass Melting Tanks Using Additionally Generated Lorentz Forces

Continuous glass melting tanks represent thermo-chemical reactors with very complex flow patterns. Controlling the flow patterns within the glass melting tanks with the aim of improving their performance is one of the glass industry primary challenges. The tank performance is basically determined by the RTD （residence time distribution） of the glass melt, which directly impacts the glass quality and energy distribution. In the present work, numerical simulations are carried out on the electromagnetic flow control to investigate how well the flow can be controlled by externally generated electromagnetic （Lorenz） forces that are added to the glass melt. Furthermore, the melting tanks are equipped with supplementary electric heating systems called ＂electric boosters＂. The desired result would be an improved RTD. The electromagnetic flow control is called ＂electromagnetic boosting＂ and can be realized by exposing the glass bath to an external magnetic field generating Lorentz forces on the glass melt as an additional flow component. The numerical simulations of the present study require coupled calculations of electromagnetic field, flow field, and temperature field, because the material properties of glass melt are strongly temperature-dependent. The computational results show that electromagnetic boosting is an excellent way of improving the RTD in glass melting tanks, ultimately resulting in better glass quality and increased productivity. Of course, the glass industry is highly interested in achieving exactly this result.

The influences of wall Lorentz force and field Lorentz force on the cylinder drag reduction

In this paper,the effects of Lorentz force on drag reduction for a circular cylinder have been studied experimentally and numerically.Based on its effects on drag reduction,the Lorentz force is found to be classified into two parts：one acts directly on the cylinder,named as the wall Lorentz force,and the other called the field Lorentz force acts on the fluid inside the boundary layer.The wall Lorentz force leads to the generation of a thrust,whereas the field Lorentz force results in drag increase.Since the former dominates the drag variation,the drag would reduce accordingly and even turn into negative （thrust） with the application of Lorentz force.

Lorentz Force from a Current-Carrying Wire on a Charge in Motion under the Assumption of Neutrality in the Symmetrical Frame of Reference

It is commonly assumed that a wire conducting an electric current is neutral in the laboratory frame of reference (the rest frame of the lattice of positive ions). Some authors consider that the wire is neutral only in a symmetrical frame of reference, in which the velocities of electrons and protons have equal norm and opposite direction. In this paper, we discuss the Lorentz transformation between different frames of reference in the context of the special theory of relativity for a current-carrying conducting wire and a probe charge in motion with respect to the wire. A simple derivation of the Lorentz force in the laboratory frame of reference for the assumed neutrality in a symmetrical frame of reference is presented. We show that the Lorentz force calculated assuming neutrality in the symmetrical frame of reference and the one assuming neutrality in the laboratory frame of reference differ by a term corresponding to a change in the test charge speed of one half the drift velocity of the electrons.

Antisymmetric planar Hall effect in rutile oxide films induced by the Lorentz force

The conventional Hall effect is linearly proportional to the field component or magnetization component perpendicular to a film. Despite the increasing theoretical proposals on the Hall effect to the in-plane field or magnetization in various special systems induced by the Berry curvature, such an unconventional Hall effect has only been experimentally reported in Weyl semimetals and in a heterodimensional superlattice. Here, we report an unambiguous experimental observation of the antisymmetric planar Hall effect(APHE) with respect to the in-plane magnetic field in centrosymmetric rutile RuO_(2) and IrO_(2) single-crystal films. The measured Hall resistivity is found to be linearly proportional to the component of the applied in-plane magnetic field along a particular crystal axis and to be independent of the current direction or temperature. Both the experimental observations and theoretical calculations confirm that the APHE in rutile oxide films is induced by the Lorentz force. Our findings can be generalized to ferromagnetic materials for the discovery of anomalous Hall effects and quantum anomalous Hall effects induced by in-plane magnetization. In addition to significantly expanding knowledge of the Hall effect, this work opens the door to explore new members in the Hall effect family.

Numerical Analysis on Lorentz Force Field in φ160 Billet Under Harmonic Magnetic Field

A method was developed to quantitatively describe the time-varying Lorentz force field induced in billet under harmonic magnetic field.Based on the numerical analysis of the Lorentz force,the numeral features were concluded, which comprised of the mean force,the maximum force,the long axis,short axis and rotation direction of ellipse,the phase difference index,and so on.Using this method,the Lorentz force field in φ160 billet under 3 Hz harmonic magnetic field were analyzed.

Electronically enhancing the long-range nanopositioning accuracy of a Lorentz force actuator

This paper presents a precision centimeter-range positioner based on a Lorentz force actuator using flexure guides.An additional digital-to-analog converter and an operational amplifier(op amp)circuit together with a suitable controller are used to enhance the positioning accuracy to the nanometer level.First,a suitable coil is designed for the actuator based on the stiffness of the flexure guide model.The flexure mechanism and actuator performance are then verified with finite element analysis.Based on these,a means to enhance the positioning performance electronically is presented together with the control scheme.Finally,a prototype is fabricated,and the performance is evaluated.This positioner features a range of 10 mm with a resolution of 10 nm.The proposed scheme can be extended to other systems.

Lorentz Force Velocimetry for Poorly Conducting Fluids-Development and Validation of a Novel Flow Rate Measurement Device

The paper demonstrated the feasibility of Lorentz Force Velocimetry for flow rate measurements of weakly conducting electrolytes using experimental results on salt water flow exposed to a permanent magnet system.This innovative flow measurement technique allows the non-contact determination of flow rates and relies on the interaction between a magnetic field and a moving conducting fluid.When an electrically conducting fluid moves through the magnetic field a Lorentz force is generated and acts on the measurement system.The present report provides an overview about the experimental setups and the first measurement results.

Numerical Analysis of Unsteady Natural Convection Flow and Heat Transfer in the Existence of Lorentz Force in Suddenly Expanded Cavity Using OpenFOAM

The present study reveals the significance of the magnetic field or Lorentz force on the unsteady natural convection flow and heat transfer in the suddenly expanded cavity.The Lorentz force based magnetohydrodynamics(MHD)solver using electric potential formulation coupled with the energy equation by the means of Boussinesq approximation is developed in the open-source CFD tool OpenFOAM.The unsteady flow is generated by the buoyancy force keeping the Rayleigh number(Ra)at 109,at the fixed Prandtl number(Pr)of 0.71.The effects of the magnetic field on the flow and heat transfer are explained for various orientations of magnetic field(Bx,B45,and By)in terms of Hartmann number(Ha=0,50,100,300 and 500).The increase in the magnetic field increases the strength of the Lorentz force,which regulates the flow pattern and suppresses down the unsteady nature of flow and heat transfer into the steady-state.It is perceived that the average Nusselt number decreases as the intensity of Bx and B45 magnetic field increases.However,for By magnetic field the average Nusselt number increases up to Ha of 100 as compared to the non-MHD case(Ha=0).The distribution of Lorentz force in the domain plays a significant role in the governing of the fluid flow and heat transfer.

Investigation of Lorentz Force Velocimetry Using Electromagnets

The present work is an analysis on the ElectroMagnetic Lorentz Force Velocimetry(EM-LFV).This noncontact flow measurement technique is based on evaluating the Lorentz force generated by the interactions of an electrically conducting fluid with a localized magnetic field that is produced by electromagnets.Analytical and numerical calculations were carried out as a continuation of a previous work published by Thess et al.The objective is to establish the behavior of the Lorentz force as a function of the main geometric parameters considered in the studied geometry. Thus we present here the evolution of the Lorentz force induced in a translating cylindrical solid body and the coefficient of sensitivity of the flowmeter thanks to numerical simulations in respect with the main geometrical parameters of the problem.

Flowrate Measurement in Turbulent Liquid Metal Channel Flow Using Time-of-Flight Lorentz Force Velocimetry:Experimental Investigations and Numerical Modeling

Lorentz force velocimetry(LFV)is a suitable non-contact technique to measure flow velocity and flowrates in electrically conducting high-temperature melts.LFV is based on the principles of magnetohydrodynamics:when an electrically conducting fluid passes the field lines produced by a magnet system,eddy currents are induced within the fluid.The interactions of the eddy currents with the magnetic field generate Lorentz forces.Using LFV the counterforce acting on the magnet system is measured.Such a flowmeter consists of a permanent magnet system and an attached digital force sensor.The force recorded by the flowmeter is proportional to the flowrate Q and depends on both the electrical conductivity σ of the fluid and the spatial distribution of the applied magnet field B.However,in metallurgical applications,σ is often unknown or fluctuates in time as it strongly depends on both temperature and composition of the melt.In the present paper we investigate a technique called Time-of-Flight Lorentz force velocimetry ToF LFV.In this technique,the flowrate can be determined by just cross-correlating the two force signals recorded by two flowmeters which are arranged one behind the other separated by a certain distance D.Sensing the passage of the triggered vortices, this ToF LFV measures the transit time τ of these vortices.Then we recalculate the velocity V according to the relation V = D/τ.We experimentally and numerically study turbulent liquid metal flow in the test facility EFCO(electromagnetic flow control channel)using the eutectic alloy GainSn as a test fluid.Our experiments show that this electromagnetic ToF LFV is well suited to determine the flow velocity and flowrate.The experiments are accompanied by numerical simulations using the commercial program package FLUENT.

Lorentz Force Sigmometry

The present communication reports a new technique for the contactless measurement of the specific electrical conductivity of a solid conductor or an electrically conducting fluid.We term the technique 'Lorentz Force Sigmometry' where the neologism 'Sigmometry' is derived fiom the Greek letter sigma,often used to denote the electrical conductivity.Lorentz force sigmometry(abbreviated LoFoS)is based on similar principles as the traditional eddy current testing but allows a larger penetration depth and is less sensitive to variations in the distance between the sensor and the sample.Here we formulate the theory of LoFoS and numerically compute the calibration function which is necessary for determining the unknown electrical conductivity from the measurement of a Lorentz force.

The Pairing Analysis Improvement of Magnetized Structure in Electromagnetic Bulging Process in Case of Tube with Field Shaper

In the current practical science, the accuracy in the formability of metal alloys being the goal when using electromagnetic forming (EMF) technology, which is a high-speed processing technology that uses Lorentz forces to achieve plastic deformation of sheet metal;according to the previous analysis, the results have shown that in most cases, the Lorentz force acting on the workpiece (metal) is not uniform, there are uneven axial deformations of the metal plates which prevent the rapid advancement of today’s technology. In this article, we presented some advanced analyzes which will lead us to improve the technical solution for the problems of non-uniform axial deformations of the metals in the traditional tube electromagnetic forming technology (EMF). A field shaper is used as a practical forming tool to influence the magnetic field and magnetic pressure distribution, thereby improving the forming ability and result during the electromagnetic forming (EMF) process and we see that induced eddy current control is realized by changing the structural parameters of the magnetic field shaper;which improves the strength and controllability of the magnetic force that acts on the workpiece;thereby a greater radial magnetic pressure can be achieved with field shaper than the case without it;the field shaper regulates the electromagnetic force, the distribution of the magnetic pressure decreases, and the uniform force area of the tube increases which effectively enhances the uniform range of the pipe electromagnetic bulging and the electromagnetic induction coupling between the coil and the metallic workpiece is generally required to produce the Lorentz forces. Using COMSOL Multiphysics® simulation software helped us to accurately represent the real world, simulating multiple physical effects that happened in this model during the process.