Chin-Cheng Wang

Bulk flow modification with horseshoe and serpentine plasma actuators

Two different control devices are introduced to modify the boundary layer thickness by plasma induced velocity in the low speed region. These horseshoe and serpentine shaped actuators are surface compliant and have a significant three-dimensional influence on neighbouring flows. A numerical investigation of the quiescent and flow condition demonstrates active electrodynamic actuation of fluid in all three principal (streamwise, crosswise and surface normal) directions altering the boundary layer thickness. Based on the powering scheme of electrodes, these actuators not only induce flow attachment to the work surface but can also extract momentum from an upstream flow injecting it into the bulk fluid. Such designs could be useful for tripping the flow as well as for separation control as needed.

Three-dimensional effects of curved plasma actuators in quiescent air

This paper presents results on a new class of curved plasma actuators for the inducement of three-dimensional vortical structures. The nature of the fluid flow inducement on a flat plate, in quiescent conditions, due to four different shapes of dielectric barrier discharge (DBD) plasma actuators is numerically investigated. The three-dimensional plasma kinetic equations are solved using our in-house, finite element based, multiscale ionized gas (MIG) flow code. Numerical results show electron temperature and three dimensional plasma force vectors for four shapes, which include linear, triangular, serpentine, and square actuators. Three-dimensional effects such as pinching and spreading the neighboring fluid are observed for serpentine and square actuators. The mechanisms of vorticity generation for DBD actuators are discussed. Also the influence of geometric wavelength (λ) and amplitude (Λ) of the serpentine and square actuators on vectored thrust inducement is predicted. This results in these actuators p...

Energy and force prediction for a nanosecond pulsed dielectric barrier discharge actuator

A three-species physical model is presented for dielectric barrier discharge (DBD) actuator under atmospheric pressure. The governing equations are solved for temporal and spatial distribution of electric potential and charge species using the finite element based multiscale ionized gas flow code. The plasma model is loosely coupled with compressible Navier-Stokes equations through momentum and energy source terms. Two cases of rf powered and nanosecond pulsed barrier discharge actuators are simulated. Based on the imparted time average electrohydrodynamic force and power deposition to the neutral gas, the nanosecond pulsed DBD actuator creates significant pressure variations within few microseconds. These results are in reasonable agreement with recently reported experimental shadow images.

Microscale plasma actuators for improved thrust density

We present a study of the dielectric barrier discharge (DBD) plasma actuators for microscale applications. Traditional macroscale DBD actuators suffer from relatively small actuation effect as characterized by small induced force density and resulting flow velocity. As a remedy we propose microscale plasma actuators that may induce orders of magnitude higher force density. We study the physics of such actuation using a multiscale ionized gas flow code based on the high-fidelity finite-element procedure. First, a two-dimensional volume discharge with nitrogen as a working gas is investigated using a first-principles approach solving coupled system of hydrodynamic plasma equations and Poisson equation for ion density, electron density, and electric field distribution. The quasi-neutral plasma and the sheath regions are identified. As the gap between electrodes is reduced, the sheath structure dominates the plasma region. Second, we simulate a first generation plasma micropump. We solve multiscale plasma-gas...

Combustion stabilization using serpentine plasma actuators

This letter presents a numerical model for combustion stabilization with plasma actuators. Recently, we demonstrated that serpentine actuators induce complex neighboring flow structures due to pinching and spreading effects suitable for rapid flow mixing. Here, the influence of serpentine plasma actuator is numerically investigated on inner and outer recirculation zones of a gas turbine combustor. Beyond benchmarking with reported experimental data, we show that the swirl generated by the serpentine plasma actuators creates local low velocity regions stabilizing the flame. Such simple flow-mixing device does not need any moving parts, hence may be useful in the any combustors.

Electrodynamic enhancement of film cooling of turbine blades

Three concepts are numerically investigated to promote lateral mixing of the cold jets and to ensure their better attachment to the surface. First, we introduce electrodynamically enhanced interaction of cool air jets with hot crossflow for improved cooling of hot surfaces. We identify mechanisms to “push” or “pull” the essentially stagnant fluid just downstream of the hole by enforcing an active pressure pulsation in streamwise and crosswise directions. Such method utilizes electrodynamic force that induces attachment of cold jet to the work surface by actively altering the body force in the vicinity using a plasma actuator for different cooling hole geometries. Second, we employ a negative pressure region just downstream of the cooling hole. This may be generated by utilizing a suction vent or other mechanisms. Third, we propose three geometric modifications of the cooling hole exit for enhancing lateral tripping of the cold jet. Detailed computation of a single row of 35 degree round holes on a flat pl...

Plasma actuated heat transfer

We introduce plasmas for film cooling enhancement in gas turbines and other engineering applications. We identify mechanisms to actuate essentially stagnant fluid just downstream of the cooling hole by employing three-dimensional body force for different hole geometries. Such methods actively alter flow structures in the vicinity of an actuator using an electrodynamic mechanism that induces attachment of cold jet to the work surface. Numerical results are compared with published experimental data and other numerical predictions for the latest film cooling technology. An effectiveness improvement of above 100% over the standard baseline design is predicted.

Three-dimensional simulation of a microplasma pump

We present a three-dimensional simulation of dielectric barrier discharge (DBD) using the finite element based multiscale ionized gas (MIG) flow code. The two-species hydrodynamic plasma model coupled Poisson equation and Navier‐Stokes equation are solved using MIG flow code to predict complicated flow structure inside a plasma induced micropump. The advantage of such a micropump is rapid on/off switching without any moving parts. Results show a reasonable distribution for ion and electron densities as well as an electric field. The key factors of microplasma pump design are the location of actuators and input voltage. The flow rate of the microplasma pump is on the order of mlmin −1 . Such a flow rate may be beneficial for micropropulsion in space. (Some figures in this article are in colour only in the electronic version)

Geometry Effects of Dielectric Barrier Discharge on a Flat Surface

We present four different shapes of dielectric barrier discharge (DBD) actuators for the inducement of fluid flow. Three-dimensional plasma governing equations have been solved based on in-house MIG flow code. We numerically test these actuators in quiescent air. Numerical results show plasma force vectors as well as detailed flow behaviors such as velocity and vorticity. Novel designs of three-dimensional (triangular, serpentine, and square) actuators produce much strong flow mixing downstream of the actuator than traditional two-dimensional (linear) actuators. Specifically, square actuator has the best performance in flow mixing than others. Three-dimensional effects such as pinching or spreading the neighboring fluid become an important index to enhance the performance of the actuator.

A Computational Diagnostic Tool for Understanding Plasma Sterilization

Plasma sterilization is fast evolving into a sought after sterilization method in industries such as medicine, biology, food and healthcare. Atmospheric, non-thermal dielectric barrier discharge (DBD) plasma poses certain advantages in terms of sterilization: it is fast, non-toxic and versatile. While abundant research deals with several different plasma types (inductive, capacitive, microwave) and their application to different kinds of bacteria and spores, the need for a deeper intuitive understanding of the fundamental plasma processes is being realized. We propose using the rate of ionization, determined by computational simulations, as a marker to obtain the killing rate in plasma sterilization processes.