Jian Wu

Harbin Institute of Technology | HIT · School of Energy Science and Engineering

Natural convection with an electric field in the classic differentially heated square cavity is numerically studied. The electric conduction model for the generation of free space charges, which applies to weak and moderate electric field with weakly conducting liquids, is specially considered. The whole set of governing equations is implemented in...

The cavitation phenomenon is an important factor affecting the safe and stable operation of hydraulic machinery units. The cavitation of the hydraulic machinery units can lead to the increased vibration, reduced efficiency, and cavitation erosion of blades. Therefore, a method is needed to determine the incipient cavitation of hydraulic machinery r...

In this paper, the effect of a non-uniform electric field on pool boiling is investigated by using the pseudopotential lattice Boltzmann model and the leaky dielectric model. The focus of the study is on the field trap effect, which drives bubbles to migrate toward regions with a lower electric field intensity. Relevant results demonstrate that the...

In this work, we present a numerical investigation of the effect of a temperature gradient on the flow characteristics of electrohydrodynamic (EHD) conduction phenomenon. The influence of temperature on the physical properties of dielectric liquids together with the dielectric force has been investigated by a dimensional simulation. To better ident...

We numerically investigated the global linear instability and bifurcations in electro-thermo-convection (ETC) of a dielectric liquid confined in a two-dimensional (2-D) concentric annulus subjected to a strong unipolar injection. Seven kinds of solutions exist in this ETC system due to the complex bifurcations, i.e. saddle-node, subcritical and sup...

The mechanical seal performance in reactor coolant pump (RCP) is of great importance for the efficient and safe operation of primary loop in nuclear power plant. The sealing medium filling inside the seal encounters strong thermal gradient. In this paper, thermo-viscous effect on sealing characteristics with two typical mechanical seal faces, namel...

In this paper, we present direct numerical simulations of viscoelastic fluid flow in a cavity with an ion conduction-driven mechanism. The flow patterns, oscillation amplitudes, force competition mode, and power-law spectral scaling accompanying oscillatory flow are examined. The dimensionless parameter β (elucidating the electric-field-enhanced di...

Latent heat thermal energy storage (LHTES) devices aid in efficient utilization of alternate energy systems and improve their ability to handle supply–demand fluctuations. A numerical analysis of melting performance in a shell-and-tube LHTES unit in the presence of a direct current (DC) electric field has been performed. The governing equations of...

A finite volume method (FVM) solver for the electric field-enhanced boiling is developed based on the OpenFoam v2012 framework. The film-boiling scenario with the influence of electric fields is numerically analyzed. By coupling the Tanasawa model and the leaky-dielectric model, the accuracy of the numerical description of the natural physical phen...

The low thermal conductivity of organic phase change materials (PCMs) has seriously obstructed the performance of thermal latent-heat thermal storage (LHTS) system. For the first attempt, we experimentally studied the phase-change heat transfer characteristics of octadecane inside a horizontal cavity with the passive addition of nano graphene and t...

The mechanisms of a charge injection-induced electrohydrodynamics (EHD) pump using the lattice Boltzmann method (LBM) is numerically investigated in this paper. The pump is composed of a dielectric liquid layer and two substrate layers with embedded electrodes. There are three possible flow modes are found, which are associated with the generation...

This paper aims to study the electro-thermo-convection of a high Prandtl number fluid (silicone oil) in a rectangular cavity. A high accuracy numerical solver is undertaken to solve the problem. These numerical simulations are performed for a range of Rayleigh and electric Rayleigh parameters, Ra=0,104∼106 and T=0∼1000, which correspond to regimes...

In this paper, a direct numerical simulation (DNS) of dielectric fluid flow subjected to unipolar injection under an alternating current (AC) electric field is carried out. The effect of frequency f of pulsed direct current (PDC) and AC on the transient evolution of electroconvection and their subcritical bifurcations are investigated in details. E...

This study set out to systematically investigate the structural characteristics of plane electrohydrodynamic jets through the particle image velocimetry (PIV) techniques. Due to the wide range of applied voltages and electrode gaps under various experimental conditions, an assessment of the image quality and a statistical analysis of the velocity f...

Film transportation driven by Electrohydrodynamic(EHD) conduction pumping has become a new prospect in many micro-scale industrial applications. This work numerically studied the electro-convection in a film induced by EHD conduction pumping. The effect of the interface charge on the heterocharge layer and the flow pattern has been carefully invest...

In this work, the electro-thermo-hydrodynamic convection system induced by unipolar charge injection between two parallel electrodes is numerically investigated. A two-relaxation-time lattice Boltzmann method coupled with a fast Poisson solver is implemented to obtain the temporal and spatial distributions of the flow field, temperature field, elec...

Abundant dynamic effects on an ion-selective surface provide a new solution for the development of microfluidic technology. If an increasing bias voltage is applied to the electrolyte solution with the ion-selective surface, the passing ion current will experience a complex nonlinear evolution. A convection phenomenon will be triggered when the imp...

This study numerically investigates the flow structures and bifurcation scenarios of three-dimensional (3D) laminar electroconvection (EC). An efficient parallel lattice Boltzmann model is undertaken to numerically solve the model problem. The results present three steady flow patterns and three pitchfork bifurcations. These three patterns each hav...

Three-dimensional (3D) electro-thermo-hydrodynamic (ETHD) flows of dielectric fluid driven by simultaneous Coulomb and buoyancy forces in a cubic box is numerically studied. The set of coupled equations associated with the ETHD phenomena are solved with finite volume method. The code is first validated by comparing the numerically obtained linear c...

We study the two-dimensional Rayleigh–Bénard instability subject to the combined effects of a solid–liquid phase boundary and shear using linear stability theory and energy analysis. We consider two thermal states of the solid (isothermal and conducting), and two types of shear that can arise in different contexts. When the melting temperature is e...

This paper presents a two-dimensional direct numerical simulation (DNS) of dielectric fluid flow subjected to unipolar injection under an alternating current (AC) electric field. The effect of frequency f of pulsed direct current (PDC) and AC on the transient evolution of electroconvection and their subcritical bifurcations are investigated for the...

Transition sequences with various flow patterns and heat transfer enhancement of a dielectric liquid layer between two parallel planar electrodes of infinite length are investigated numerically. External electric field and internal temperature field are considered to be two independent driving factors of the flow, while unipolar charge injection vi...

The mechanism of an EHD wall jet generated by a surface dielectric barrier injection (SDBI) actuator remains to be elucidated due to asymmetry of the electrode structure and existence of the dielectric layer. Taking into account the charge injection and dissociation mechanisms as well as the surface charge accumulation effect, an EHD wall jet model...

The Space Plasma Environment Research Facility aims to research the space plasma physics in the laboratory. Two elliptical magnets are used to form a magnetic mirror field simulating the interplanetary magnetic field to investigate the magnetic reconnection at the magnetopause and magnetotail of the earth on the ground. To perform the research, the...

In the present study, two schemes named face discernment and flux correction are proposed to achieve single-phase transportation of free charge in multiphase electrohydrodynamic(EHD) problems. Many EHD phenomena occur between air and another liquid while the free charge can only be transported in the liquid phase through ohmic conduction and convec...

Modal global linear stability analysis of thermal convection is performed with the linearized lattice Boltzmann method (LLBM). The onset of Rayleigh–Bénard convection in rectangular cavities with conducting and adiabatic sidewalls and the instability of two-dimensional (2-D) and three-dimensional (3-D) natural convection in cavities are studied. Th...

In this work, a two-dimensional droplet confined between two parallel electrodes under the combined effects of a nonuniform electric field and unipolar charge injection is numerically investigated using the lattice Boltzmann method (LBM). Under the non-Ohmic regime, the interfacial tension and electric forces at the droplet surface cooperate with t...

Direct numerical simulations of electroconvection instability near an ion-selective surface are conducted using a mesoscopic lattice Boltzmann method (LBM). An electrohydrodynamic model of ion transport and fluid flow is presented. We numerically solve the Poisson-Nernst-Planck equations for the electric field and the NavierStokes equations for the...

In this paper, a detailed two-dimensional numerical study on the nonlinear behaviors of electrohydrodynamic flows of Oldroyd-B viscoelastic dielectric liquid between two coaxial cylinders is conducted. The liquid is subjected to strong unipolar injection from inner annulus. The entire set of coupled equations, including the Navier-Stokes equations,...

Unstable flow within a reactor coolant pump (RCP)’s mechanical seal may cause the change of its sealing parameters, possibly threatening RCP’s safe operations. In this study, based on the moving grid technology, a 3D fluid–structure interaction analysis model is established, where the influence of parameters such as the inlet pressure fluctuation,...

Direct numerical simulations and linear stability analysis are performed to study the three-dimensional electro-thermo-convective (ETC) flow between two parallel plates under a simultaneously applied temperature difference and voltage. Entropy generation analysis and hexagonal pattern analysis are used to illustrate the transient evolution and stat...

Injection-induced electro-convection (EC) of dielectric liquids is a fundamental problem in electrohydrodynamics. However, most previous studies with this type of EC assume that the liquid is perfectly insulating. By perfectly insulating, we mean an ideal liquid with zero conductivity, and in this situation, the free charges in the bulk liquid orig...

A dipole magnet is designed in the SPERF to create the magnetic field for simulating the large-scale magnetosphere of the earth. The design and construction process of the dipole magnet is presented here to settle the issues in regard to electricity, vacuum, and support, etc. Several measures are taken to improve the magnet's insulation performance...

Liquid based cooling has become a new prospect in the thermal management of electronic devices. This work numerically investigates the potential of EHD conduction pumping to remove heat from a high density flux heat source, as commonly encountered in electronic cooling applications. A 2 − D horizontal plate configuration with a heated patch releasi...

The externally imposed direct current (DC) electric field mightily impacts on the conjugate heat transfer existing somewhere between the solid and liquid phases, which is numerically investigated via Lattice Boltzmann method (LBM) in this paper. The model is a square cavity filled with dielectric liquid, in which has a centred heat-generating solid...

In this paper, a numerical investigation of bubble dynamics during nucleate pool boiling is conducted using the lattice Boltzmann method (LBM). Unlike the perfectly dielectric fluid assumption used in most previous studies, the leaky-dielectric model (LDM) used in this work allows free charges to accumulate at the gas-liquid interface and more clos...

Despite the valuable previous studies on energy harvesting from flutter instability, no decisive ranking still exists between fluttering generators and harvesters based on other Flow-Induced Vibration (FIV) instabilities. In the current empirical study, the hydroelastic response and the energy performance of a self-sustained NACA 0015 hydrofoil are...

Although the issue of charge formation mechanisms is a major area of interest within the field of electrohydrodynamic (EHD) flows, no attempt has been made to quantitatively investigate theoretical models from the perspective of electrode processes. This paper aims to provide a novel simulation model considering both electrochemical injection and f...

In this work, the electrohydrodynamic instability induced by a unipolar charge injection is extended from a single-phase dielectric liquid to a two-phase system that consists of a liquid-air interface. A volume-of-fluid model-based two-phase solver was developed with simplified Maxwell equations implemented in the open-source platform OpenFOAM. The...

As an advanced flow control and generation technology, electrohydrodynamic (EHD) pumping has received extensive attention in recent years. EHD conduction pumping is a type of EHD pumping that makes use of electric Coulomb force produced by an applied electric field and heterocharge layers formed near the electrodes in dielectric liquids. In this pa...

Due to the Onsager–Wien effect (enhanced electric field dissociation), electrohydrodynamic (EHD) conduction pumping problems in the Oldroyd-B viscoelastic dielectric liquid are solved using the finite volume method. Fully coupled nonlinear equations, including the Naiver–Stokes (N–S) equation, the Nernst–Plank equation of the ion conduction mechani...

Preclinical imaging with photoacoustic tomography (PAT) has attracted wide attention in recent years since it is capable of providing molecular contrast with deep imaging depth. The automatic extraction and segmentation of the animal in PAT images is crucial for improving image analysis efficiency and enabling advanced image post-processing, such a...

In this study, we experimentally inquire into the mechanism of the electric field for heat transfer enhancement by a point-to-ring corona gas discharge with either positive or negative applied voltage. We use a self-assembly 2D2C particle imaging velocimetry system to visualize and record the flow field. Results show that in our configuration the o...

In this paper the melting heat transfer process of n-octadecane when confined in a cylinder-cubic cavity under the influence of an electric field is experimentally investigated. N-octadecane is a typical organic phase change material (PCM) and possesses a well-defined melting point. The cylinder is subject to the simultaneous actions of electric po...

A R T I C L E I N F O Keywords: Organic phase change materials (PCMs) Melting Combined heat transfer enhancement technique Fin Electric field Particle image velocimetry (PIV) A B S T R A C T This work extends our recent study (Sun et al., 2021 [1]) on the n-octadecane's melting with electric field inside a cavity. The combined heat-transfer enhance...

In this work, the electrohydrodynamic (EHD) instability induced by a unipolar charge injection is extended from a single-phase dielectric liquid to a two-phase system that consists of a liquid-air interface. A volume of fluid (VOF) model based two-phase solver was developed with simplified Maxwell equations implemented in the open-source platform O...

The two-dimensional regular and chaotic electro-convective flow states of a dielectric liquid between two infinite parallel planar electrodes are investigated using a two-relaxation-time lattice Boltzmann method. Positive charges injected at the metallic planar electrode located at the bottom of the dielectric liquid layer are transported towards t...

Experiments on the melting characteristics of n-octadecane with electric field inside a cavity are carried out. The classical differentially heated cavity is considered to explore the effect of electric field on solid-liquid phase change heat transfer. The influence of the applied voltage's polarity and magnitude on the melting process of n-octadec...

The spatial resolution of photoacoustic tomography (PAT) can be characterized by the point spread function (PSF) of the imaging system. Due to the tomographic detection geometry, the PAT image degradation model could be generally described by using spatially variant PSFs. Deconvolution of the PAT image with these PSFs could restore image resolution...

In this study, a lattice Boltzmann method (LBM) is extended for the problem of electrohydrodynamic (EHD) solid-liquid phase change in a square cavity. Four unified lattice Boltzmann equations (LBEs) are used to solve the fully coupled mathematical equations, including the Navier-Stokes equations, the energy conservation equation, the Poisson’s equa...

Electrokinetic flow in a microchannel driven by charged surface heterogeneity in the presence of an external electric field is investigated by three-dimensional simulations. A computational framework is developed coupling a two-relaxation-time lattice Boltzmann solver for the transport equations of fluids, charged species, and passive tracing scala...

Two commonly used discrete velocity models [the linear discrete velocity model (LDVM) and the full discrete velocity model (FDVM)] are investigated using the two-relaxation time lattice Boltzmann method coupled to a fast Poisson solver in an electroconvection system. We derived analytically the LDVM, i.e., D2Q5 and D3Q7 and FDVM, i.e., D2Q9 and D3Q...

The two-dimensional (2D) electro-convection (EC) flow of dielectric liquids between two concentric cylindrical electrodes driven by unipolar injection of ions is investigated numerically. The finite volume method is used to resolve the spatiotemporal distributions of the flow field, electric field, and charge density. The flow transition routes fro...

Magnetic resonance imaging (MRI) and photoacoustic tomography (PAT) are two advanced imaging modalities that offer two distinct image contrasts: MRI has a multi-parameter contrast mechanism that provides excellent anatomical soft tissue contrast, whereas PAT is capable of mapping tissue physiological metabolism and exogenous contrast agents with op...

A numerical investigation of electro-thermo-convection in a 2 − D differentially heated square cavity filled with a dielectric liquid is presented. Fully coupled governing equations of electric potential, charge transport, Navier–Stokes equations, and the energy equation are implemented in the finite-volume framework of Open�FOAM®. For this kind...

Electrothermohydrodynamic convection driven by strong unipolar charge injection in the presence of a stabilizing inverse thermal gradient between two parallel electrodes is investigated by a linear stability analysis and a numerical simulation. The generalized Schur decomposition is used to solve for the eigenvalues of the linearized system reveali...

There has been a remarkably increasing interest in applying acoustofluidics in micro-electro-mechanical systems and lab-on-a-chip systems in the past decades. This paper investigated the heat transfer performance in a straight microchannel heat sink which applies standing surface acoustic waves (SSAW) to disturb the flow. Two-dimensional numerical...

A numerical investigation of electrohydrodynamic flows of a dielectric liquid in a single wire–plate configuration with a cross Poiseuille flow has been presented. Unipolar charge injection takes place from a metallic wire electrode immersed in a dielectric liquid at the center of the channel. Although this configuration is frequently studied with...

In recent times, transverse Flow Induced Vibration (FIV) has emerged as a promising technique for energy harvesting from fluid motion. However, relatively low harnessed power and efficiency remain as major challenges. Although several studies on hydrokinetic energy harvesting of circular oscillators at the wake of similar cylinders are reported in...

This paper investigates the steady coherent solutions, bifurcated from the linear stability of a stationary flow, in 2D penetrative convection. Results show that the thickness of the upper stably stratified layer, which is measured by a dimensionless temperature θ M (the temperature at which the density is maximal), plays an important role in the l...

The mechanism of surface charge convection (SCC) reveals inherently nonlinear coupling between the electrostatic problem and the hydrodynamic flow in the Melcher–Taylor electrohydrodynamic (EHD) model. Considering that most previous numerical models are based on decoupled leaky dielectric equations, the quantitative effect of SCC on two-phase EHD u...

Recent experimental results demonstrate that electric field can effectively decrease the melting time of dielectric Phase Change Materials (PCMs). In this study, a Finite-Volume Method (FVM) based numerical model for the solid-liquid phase change heat transfer of dielectric PCM under the influence of electric field is presented. Fully coupled gover...

Electro-thermo-convection is a typical interdisciplinary problem, that has been widely studied in terms of its physical phenomena in Newtonian fluids. As an essential supplement to the study of electrohydrodynamics, electro-thermo-convection in power-law fluids within rectangular enclosures is investigated in this paper. Two geometrical configurati...

Owing to an inconsistent load demand, hydraulic turbines are often operated under off-load range. Resultant flow instabilities comprise low-frequency pressure fluctuations, which are dependent on the operating condition and unavoidable high-frequency fluctuations evolving from the interactional design concept of hydrofoils. Through the analysis of...

Experiments on the electrohydrodynamic (EHD) flow characteristics of a dielectric liquid in a sharp needle-plate configuration under direct current (DC) and alternating current (AC) electric field are carried out. The current-voltage characteristics and the velocity field are simultaneously recorded for understanding the flow behavior and its mecha...

The 1D hydrostatic base state of electroconvection driven by unipolar charge injection between two parallel electrodes is investigated using a finite difference method. A boundary layer near the anode surface is derived analytically. The computational grid is required to resolve this boundary layer to maintain high order accuracy.