Induced Body Force Research Articles

Traction-Associated Peridynamic Motion Equation and Its Verification in the Plane Stress and Fracture Problems

How to prescribe traction on boundary surface is still an open question in peridynamics. This problem is investigated in this paper. Through introducing the induced body force defined by boundary traction, the Silling's peridynamic motion equation is extended to a new formulation called the traction-associated peridynamic motion equation, which is verified to be compatible with the conservation laws of linear momentum and angular momentum. The energy conservation equation derived from the traction-associated peridynamic motion equation has the same form as that in the original peridynamics advanced by Silling. Therefore, the constitutive models of the original peridynamics can be directly applied to the traction-associated peridynamic motion equation. Some benchmark examples in the plane stress problems are calculated. The numerical solutions agree well with the classical elasticity solutions, and the volume correction and the surface correction are no longer needed in the numerical algorithm. These results show that the traction-associated peridynamic motion equation not only retains all advantages of the original peridynamics, but also can conveniently deal with the complex traction boundary conditions.

Electrostatic Body Forces and their Implications for Cracks

AbstractA Griffith‐type crack in a dielectric solid under electromechanical loading is investigated by numerically solving the combined boundary value problem. The focus is on the contribution of electrostatically induced body forces, coming along with the still controversially discussed Maxwell stress tensor, to the crack tip loading. A 1/r‐singularity of compressive stress is found to evolve at the crack tip, however, just being dominant over the mechanically induced 1/√r‐behavior within a very small region.

Pulsed Velocity Created by a Plasma Actuator in the Vicinity of the Wall

Surface dielectric barrier discharge plasma actuators, which have a few advantages and are involved in continuous and burst modes, have attracted worldwide attention for aircraft flow control in the last two decades. It is believed that understanding the flowfield generated by surface dielectric barrier discharge plasma actuators has a great effect on promoting the control effects of plasma actuators. Nevertheless, the details of the flowfield close to the wall remain unclear. Motivated by this requirement, the flowfield created by a single asymmetrical plasma actuator is investigated in still air by using the two-dimensional time-resolved particle image velocimetry device. Interestingly, a pulsed velocity created by the plasma actuator with the continuous mode near the dielectric surface is first observed, which might cause the impact effect by creating large-size disturbances, and benefits flow control. It is speculated that the formation of the pulsed velocity is related to the coupling effect between the entrainment of the starting vortex and the induced body force at the initiation stage closely. In addition, the present results reveal the underlying mechanism that the control effect of the burst pattern has significantly outperformed that of the continuous one.

Formation Mechanism of Wall Jet Generated by Plasma Actuators in Quiescent Air

Flow control technology using dielectric barrier discharge plasma actuators stimulated by a sinusoidal alternating current (AC) high-voltage power supply has been studied explosively during the last two decades in the aerospace area for promoting the aerodynamics performance of the airplane. For the purposes of uncovering the controlling mechanism and enhancing the control effect of plasma actuators, the formation mechanism of the wall jet produced by plasma actuators in still air is studied by using a high-frequency particle image velocimetry system, a pressure-field microphone, and a high-accuracy phase-lock image freezing Schlieren technique. The discharge of the plasma actuator is mainly involved in the streamer discharge and the glowlike discharge during one sinusoidal AC period. It is found that the acoustic streaming flow generated by the plasma actuator lifts the airflow, and the body force generated by the plasma actuator pushes the airflow, during the streamer discharge stage. In addition, the airflow is drawn by the entrainment and pushed by the induced body force, respectively, during the glowlike discharge stage. Based on the body force and acoustic streaming flow, the influences of the plasma actuator on quiescent air are summarized as lift–push–push behavior.

Evaluation of Cylindrical Asymmetric Surface Dielectric Barrier Discharge Actuators for Surface Decontamination and Mixing

Surface dielectric barrier discharge (SDBD) was used to evaluate cylindrical plasma actuators for inactivation of Salmonella enterica. A cylindrical SDBD configuration was evaluated to determine if the inherent induced body force could be leveraged to impel plasma species, such as reactive oxygen and nitrogen species (RONS), as an apparatus to sterilize surfaces. The cylindrical structure is evaluated in this study to observe whether an increase in mixing is possible to efficiently distribute the plasma species, thereby improving bacterial inactivation efficiency. The increase in induced airflow of SDBD actuators with increased numbers of electrodes correlates with increased bacterial inactivation. These results suggest that improving the particle velocity, airflow mixing tendencies, and plasma volume for the same power inputs (same net power to the actuators) results in increased surface decontamination efficiency.

Characteristics of a dielectric barrier discharge plasma actuator driven by pulsed-DC high voltage

Dielectric barrier discharge using pulsed-DC high voltage (pulsed-DC DBD) have been proven to be capable of effectively reducing skin friction drag in turbulent boundary layers with limited power consumption, thus producing significant net power savings. In this work, the characteristics of pulsed-DC DBD, including power consumption, induced flow structure, thermal effect, and body force, are investigated sequentially. Both the power consumption and pressure waves produced by pulsed-DC DBD are similar to that of DBD using nanosecond pulses (ns-DBD), whereas the wall-bounded jet structure resembles that of DBD using sinusoidal high voltage (ac-DBD). A curved wall jet is induced at a small pulse width, which turns into a straight one due to the combined effect of momentum and thermal addition when the pulse width increases. With increasing pulse width, the induced body force goes up while the thermal effect weakens. Although pulse frequency has no impact on the wall-bounded jet topology, the body force increases with pulse frequency because of the enhanced energy entrainment. With these results, four parameters that affect the performance of pulsed-DC DBD are extracted, including the pulse leading edge, pulse width, frequency, and amplitude, which lays the foundation for the optimization of pulsed-DC DBD.

Effect of pulse width on the characteristics of a dielectric barrier discharge plasma actuator driven by high-voltage pulses

In this study, high-voltage pulses are used to drive dielectric barrier discharge plasma actuators (DBDAs) for flow control purposes. The rising/falling edges of the pulse are kept nearly constant in nanosecond timescale, while the pulse width is varied from nanosecond to microsecond timescale. The impact of pulse width on the characteristics of the DBDA is investigated experimentally with a high-speed schlieren system and a high-fidelity force balance. In the case of small pulse width, a pressure wave propagating at the local speed of sound is produced each time at discharge ignition, and a vertical jet plume is induced after multiple discharge pulses due to heat accumulation (buoyancy effect). As a comparison, for cases with large pulse widths, two pressure waves are created sequentially with a time lag close to the pulse width, and a starting vortex followed by a near-wall jet is produced, demonstrating that significant momentum similar to that of DBD driven by sinusoidal high voltage has been imparted to the near-wall flow. A proportional increase of the induced body force with the cube root of the pulse width is demonstrated, while the pulse energy decreases nonlinearly as the pulse width increases. The maximum body force of 2.49 mN m−1 is reached at a pulse width of 380 μs.

Simulations of flow separation control numerically using different plasma actuator models

This study investigates the active flow control on NACA0012 airfoil numerically by introducing dielectric barrier discharge (DBD) plasma actuators. The flow over the airfoil simulations were performed using ANSYS program for free-stream velocity 14.6 m/s at wide range of angle of attacks (from 0 to 20 degrees) on NACA0012 airfoil with applied voltage 16 kV across the electrodes. There are several plasma actuator models, which simulate the effect of the plasma actuator. This paper focuses on two numerical methods: Shyy model and Suzen model. They depend on calculating the induced body force of the plasma and import it in Navier Stokes equation as an external body force. Mesh independence study is performed on the airfoil and validate the results without plasma activation with the experimental results. Two actuators were added at positions 0.1 and 0.3 of the chord length to the airfoil and an investigation is performed on the lift CL and drag Cd coefficients of the airfoil without and with the presence of the plasma. A comparison between the numerical results of the two different plasma simulation models is performed to check the accuracy of each model and the two simulation models give nearly the same results. Shyy model is recommended to simulate this type of flow due to its simplicity, faster convergence and accuracy.

Forebody asymmetric vortex control with extended dielectric barrier discharge plasma actuators**Project supported by the National Natural Science Foundation of China (Grant Nos. 51607188 and 61971345), the Foundation for Key Laboratories of National Defense Science and Technology, China (Grant No. 614220202011801), the Natural Science Basic Research Program of Shaanxi Province of China (Grant No. 2019JM-393), and Xi’an Municipal Science and Technology

Plasma control of forebody asymmetric vortices is mostly achieved by means of dielectric barrier discharge (DBD) plasma actuators. However, DBD actuators suffer from some disadvantages such as a weak induced body force, a single-direction induced jet, and an unclear control mechanism. We carry out wind tunnel experiments involving the forebody vortex control of a slender body at high angles of attack using an innovative extended DBD actuator, which has a stronger capacity to induce an electric wind than a DBD actuator. Through synchronous measurements of the pressure distribution and particle image velocimetry (PIV), the spatiotemporal evolution of the dynamic interactions between plasma-actuation-induced vortices and forebody asymmetric vortices is analyzed. The influence of plasma discharge on the boundary layer separation around a slender body and the spatial topological structures of asymmetric vortices are further surveyed, as the optimized actuation parameters. Extended DBD actuators are found to be more capable of controlling asymmetric vortices than DBD actuators, and a linear proportionality of the sectional lateral force versus the duty ratio is achieved. There exists an optimal normalized reduced frequency (f+ = 2π fpd/U∞ = 2.39) for asymmetric vortex control under the present experimental conditions. The research results can provide technical guidance for the control and reuse of forebody asymmetric vortices.

Influence of actuation parameters of multi-DBD plasma actuators on the static and dynamic behaviour of an airfoil in unsteady flow

The purpose of this paper is to perform a numerical study regarding the implementation of dielectric barrier discharge plasma micro-actuators for load alleviation on a NACA 23012 oscillating blade in a freestream flow.The work aims to evaluate the feasibility of using multiple dielectric barrier discharge (multi-DBD PAs) plasma actuators as a novel approach for load alleviation and stability control of airfoils in unsteady flow. A 6-actuators configuration, positioned at the trailing edge, is designed and tested. In this configuration, half of the actuators operate on the suction surface and the others on the pressure surface.In particular, the actuators located on the suction surface reduce the airfoil lift force if the induced body force is in a direction that is opposite of the main flow, because they lead to a slight and local increment of pressure on the surface. Instead, when actuators produce a body force aligned with the streamwise direction, they lead to a slight reduction of pressure, increasing lift. Contrarily, the actuators located on the pressure surface increase the lift, if the induced body force is in the direction opposite of the flow and reduce the lift in the opposite case. The effects of plasma actuators on the flow are incorporated into Navier–Stokes equations as a body force vector into the momentum equation.Different switching on/off laws of the actuators have been are compared, in order to reduce the loads amplitude of the airfoil, and to increase the stability of the blade response to the flow, and thus, alleviating fatigue phenomena on the blade and enhancing its aeroelastic stability. The effect of the phase of the plasma actuators switching law was evaluated for different pitching oscillation reduced frequencies, ranging from 0.1 to 0.5.The results underline the capability of DBD-PAs to control and reduce unsteady loads on an oscillating airfoil, improving also the airfoil stability if the phase of the actuation force is optimized for each pitching oscillation reduced frequency.

Control of crossflow instability over a swept wing using dielectric-barrier-discharge plasma actuators

This paper investigates the potential use of dielectric-barrier-discharge (DBD) plasma actuators to control the crossflow instability of the boundary layer on a 45° swept NLF-0415 airfoil at −4∘ angle of attack.The disturbance evolution is resolved using nonlinear parabolized stability equations (NPSEs). Actuators are mounted near the leading edge and generate an electric wind perpendicular to the crossflow vortex axes. The spanwise distance between neighboring actuators is first set to be the fundamental wavelength of the unstable mode. This harmonic actuation reduces the disturbance energy only when the induced body force and the disturbance velocity have reverse sign. At certain different locations, the actuators can actually increase the disturbance energy. The robustness in laminar flow control is improved when two actuators per fundamental wavelength are used. This subharmonic actuation leads to reduction in the energy of the primary unstable mode independent of the actuator locations. Finally, the simulation without baseflow forcing reveals that harmonic modes play important roles in this subharmonic control.

Rarefied gas electro jet (RGEJ) micro-thruster for space propulsion

This article numerically investigates a micro-thruster for small satellites which utilizes plasma actuators to heat and accelerate the flow in a micro-channel with rarefied gas in the slip flow regime. The inlet plenum condition is considered at 1 Torr with flow discharging to near vacuum conditions (<0.05 Torr). The Knudsen numbers at the inlet and exit planes are ~0.01 and ~0.1, respectively. Although several studies have been performed in micro-hallow cathode discharges at constant pressure, to our knowledge, an integrated study of the glow discharge physics and resulting fluid flow of a plasma thruster under these low pressure and low Knudsen number conditions is yet to be reported. Numerical simulations of the charge distribution due to gas ionization processes and the resulting rarefied gas flow are performed using an in-house code. The mass flow rate, thrust, specific impulse, power consumption and the thrust effectiveness of the thruster are predicted based on these results. The ionized gas is modelled using local mean energy approximation. An electrically induced body force and a thermal heating source are calculated based on the space separated charge distribution and the ion Joule heating, respectively. The rarefied gas flow with these electric force and heating source is modelled using density-based compressible flow equations with slip flow boundary conditions. The results show that a significant improvement of specific impulse can be achieved over highly optimized cold gas thrusters using the same propellant.

Parametric Optimization of Multi-Electrode Plasma Actuator with Serrated Electrode

The thrust performance of the multi-electrode plasma actuator has been investigated and optimized in terms of the configuration of the actuator element and the driving conditions, from the viewpoint of electrical mobility of ions. A trielectrode plasma actuator that has two exposed electrodes with serration in bilateral symmetry was used in this study. The induced body force of the plasma actuator was investigated on quiescent air, by measuring thrust of the induced jet. With the experimental results, the physical factors that affect the growth of thrust is considered, by estimating total momentum of ions from their drift velocity.

Turbulent jet flow generated downstream of a low temperature dielectric barrier atmospheric pressure plasma device.

Flowing low temperature atmospheric pressure plasma devices have been used in many technological applications ranging from energy efficient combustion through to wound healing and cancer therapy. The generation of the plasma causes a sudden onset of turbulence in the inhomogeneous axisymmetric jet flow downstream of the plasma plume. The mean turbulent velocity fields are shown to be self-similar and independent of the applied voltage used to generate the plasma. It is proposed that the production of turbulence is related to a combination of the small-amplitude plasma induced body forces and gas heating causing perturbations in the unstable shear layers at the jet exit which grow as they move downstream, creating turbulence.

Optimization of micro single dielectric barrier discharge plasma actuator models based on experimental velocity and body force fields

Recently, the Micro Single Dielectric Barrier Discharge Plasma Actuator has become attractive for application in aeronautics and micropopulsion thrusters. The present work carried out a preliminary characterization of such device, acting on initially quiescent air by experimental and numerical approaches. Sinusoidal voltage excitation with amplitude up to 7kV and frequency up to 2.5kHz was applied. The induced flow was investigated by particle image velocimetry and the measured velocity fields were used to estimate experimentally the time-averaged induced body force distributions by a differential method. Plasma induced forces were modeled by following three different approaches, later implemented as a source term in the Navier–Stokes equations for the fluid flow simulations. Potentialities, advantages and disadvantages of the considered force modeling methods were investigated. Quantitative comparison of the experimental and numerical induced force, as well as of the velocity fields, allowed establishing which model best predicted the actuator effects. The algebraic Dual Potential Model provided a good agreement between experimental and simulated results, in terms of flow velocities and thickness of the induced wall-jet. The downstream decay of the wall-jet velocity, experimentally observed, was also successfully predicted. A maximum induced velocity of ≈2 m/s was obtained and a jet thickness of ≈3 mm.

Analytic derivation of electrostrictive tensors and their application to optical force density calculations

Using multiple scattering theory, we derived for the first time analytical formulas for electrostrictive tensors for two dimensional metamaterial systems. The electrostrictive tensor terms are found to depend explicitly on the symmetry of the underlying lattice of the metamaterial and they also depend explicitly on the direction of a local effective wave vector. These analytical results enable us to calculate light induced body forces inside a composite system (metamaterial) using the Helmholtz stress tensor within the effective medium formalism in the sense that the fields used in the stress tensor are those obtained by solving the macroscopic Maxwell equation with the microstructure of the metamaterial replaced by an effective medium. Our results point to some fundamental questions of using an effective medium theory to determine optical force density. In particular, the fact that Helmholtz tensor carries electrostrictive terms that are explicitly symmetry dependent means that the standard effective medium parameters cannot give sufficient information to determine body force density, even though they can give the correct total force. A more challenging issue is that the electrostrictive terms are related to a local effective wave vector, and it is not always obtainable in systems with boundary reflections within the context of a standard effective medium approach.

S0530204 鋸歯多電極プラズマアクチュエータの噴流特性

The objective of this research is to demonstrate the advantage and characterize the thrust performance and the induced flow field generated by the TED plasma actuator with sawtooth electrode. The induced body force of the sawtooth TED plasma actuator was investigated on quiescent air, by measuring thrust of the induced jet. A time-resolved PIV was used to acquire velocity field. From the results of the thrust measurement, it was confirmed that the sawtooth TED actuator enhances the thrust compared to the straight-edge TED actuator. From the PIV analysis, it was clearly found that the sawtooth TED actuator generates uniform facing jet from both of the electrode, by the uniform generation of the plasma from the sawtooth vertexes.

Simulating plasma actuators in a channel flow configuration by utilizing the modified Suzen–Huang model

Objective: The present investigation is an attempt to simulate a channel flow driven by two plasma actuators placed on top of each other.Methodology: The model utilizes a modified form of the Suzen-Huang plasma actuator which accounts for a 'dielectric shielding' boundary condition for the potential governing the electric field. In addition, the Fokker-Planck (drift-diffusion) characteristics were implemented on the potential governing the surface charge density.Results: The model is able to correctly predict the maximum velocities for channel flow at larger channel heights. However, at lower channel heights, the model underestimates the maximum velocities.Analysis and Discussion: An analysis of the body force profile at the centreline region in the vicinity of the plasma actuators indicated that negative vertical body forces may have contributed to the discrepancies. Following this observation, a hypothetical model which does not account for vertical body force contributions on the fluid domain was simulated. While the results from this hypothetical model show marginally improvements to the maximum induced velocities at larger channel heights in relation to experimental data, the model still underpredicts the velocity magnitude at lower channel heights. This could point to the presence of interactions between the induced body force of the top and bottom actuators, specifically at lower channel heights, that have not been captured in the present model.

Velocity-information-based force-term estimation of dielectric-barrier discharge plasma actuators

Particle image velocimetry measurements in close proximity to dielectric-barrier discharge plasma actuators are conducted to quantify the momentum transfer of the plasma to the surrounding air flow. Based on these data a comparative analysis of six existing approaches to estimate the induced body force is presented. Integral methods calculate an integral value for the actuator force based on the momentum-balance equation. Insight into the spatial distribution of the body force is provided by differential methods, which are based either on the Navier–Stokes equations or on the vorticity equation. It is demonstrated that the intensity as well as the domain of the force increase with increasing operating power levels. Emphasis is also placed on the issue of self-induced drag. It is shown that 30% of the induced momentum is consumed by wall friction. All results are validated with previously obtained balance force data and luminosity analysis of identical actuators.

Modeling and simulation of electrification delivery in functionalized textiles in electromagnetic fields

This work investigates the deformation of electrified textiles in the presence of an externally supplied magnetic field (Bext). The electrification is delivered by running current (J) through the fibers from an external power source. Of primary interest is to ascertain the resulting electromagnetic forces imposed on the fabric, and the subsequent deformation, due to the terms J×Bext and PE, where P is the charge density, E is the electric field and the current given by J=σ(E+v×Bext), where σ is the fabric conductivity, and v is the fabric velocity. As the fabric deforms, the current changes direction and magnitude, due to the fact that it flows through the fabric. The charge density is dictated by Gauss’ law, ∇·D=P, where D=ϵE,ϵ is the electrical permittivity and D is the electric field flux. In order to simulate such a system, one must solve a set of coupled equations governing the charge distribution, current flow and system dynamics. The deformation of the fabric, as well as the charge distribution and current flow, are dictated by solving the coupled system of differential equations for the motion of lumped masses, which are coupled through the fiber-segments under the action of electromagnetically-induced forces acting on a reduced order network model. In the work, reduced order models are developed for (a) Gauss’ law (∇·D=P), (b) the conservation of current/charge, ∇·J+∂P∂t=0, and (c) the system dynamics, ∇·T+f=ρdvdt, where T is the Cauchy stress and f represents the induced body forces, which are proportional to PE+J×Bext. A temporally-adaptive, recursive, staggering scheme is developed to solve this strongly coupled system of equations. We also consider the effects of progressive fiber damage/rupture during the deformation process, which leads to changes (reduction) in the electrical conductivity and permittivity throughout the network. Numerical examples are given, as well as extensions to thermal effects, which are induced by the current-induced Joule-heating.