M. Abdollahzadeh

Two-dimensional numerical modeling of interaction of micro-shock wave generated by nanosecond plasma actuators and transonic flow

Abstract The influence of nanosecond pulse-driven, surface-mounted dielectric barrier discharge (DBD) actuators on a transonic flow is studied numerically. An airfoil representing turbomachinery blades in transonic flow is considered as a test case. A two-dimensional fluid model of DBD is used to describe the plasma dynamics. The model couples fluid discharge equations with compressible Navier–Stokes equations. Simulations were conducted with an airfoil of NACA 3506 profile in a transonic condition of M = 0.75 . When a nanosecond pulse voltage is used, with a rise and a decay time of the order of nanoseconds, a significant amount of energy is transferred in a short time from the plasma to the fluid, which leads to the formation of micro-shock waves and therefore to the modification of flow features. Moreover, a plasma energy deposition model is developed and presented by using the results of the plasma discharge model.

Numerical modeling of coanda effect in a novel propulsive system

Coanda effect (adhesion of jet flow over curved surface) is fundamental characteristics of jet flow. In the present paper, we carried out numerical simulations to investigate Coanda flow over a curved surface and its application in a newly proposed Propulsive system “A.C.H.E.O.N” (Aerial Coanda High Efficiency Orienting jet Nozzle) which supports thrust vectoring. The ACHEON system is presently being proposed for propelling a new V/STOL airplane in European Union. This system is based on cumulative effects of three physical effects such as (1) High speed jet mixing speeds (2) Coanda effect control by electrostatic fields (3) Coanda effect adhesion of an high speed jet to a convex surface. The performance of this nozzle can be enhanced by increasing the jet deflection angle of synthetic jet over the Coanda surface. This newly proposed nozzle has wide range of applications. It can be used in industrial sector such as plasma spray gun and for direct injection in combustion chamber to enhance the efficiency of the combustion chamber. Also, we studied the effect of Dielectric barrier discharge (DBD) plasma actuators on A.C.H.E.O.N system. Dielectric barrier discharge (DBD) plasma actuators are active control devices for controlling boundary layer and to delay the flow separation over any convex surfaces. Computations were performed under subsonic condition. Two dimensional CFD calculations were carried out using Reynolds averaged Navier stokes equations (RANS). A numerical method based on finite volume formulation (FVM) was used. SST k-ω model was considered to model turbulent flow inside nozzle. DBD model was used to model the plasma. Moreover, a body force treatment was devised to model the effect of plasma and its coupling with the fluid. This preliminary result shows that, the presence of plasma near Coanda surface accelerates the flow and delays the separation and enhances the efficiency of the nozzle.

Numerical Simulation of a Direct Methanol Fuel Cell through a 1D+1D Approach

Reasonable performance estimation of fuel cell systems with the aid of simple fast and accurate models is necessary for optimized design process of fuel cells. To this end, a quasi two-dimensional (1D+1D), multi-component model is developed in order to analyze the two-phase transport direct methanol fuel cell (DMFC). The effects of diffusion and the mixed potential due to methanol crossover through the membrane are also considered. Different operating parameters, including temperature and the methanol feed concentration are examined and their effects are discussed. The present simple and easy to implement model can be as accurate as a complete two-dimensional model. Furthermore, it is seen that the simplification made in this model reduce the computational time and is therefore suitable for inclusion in real-time system level DMFC calculations.

(1D + 1D) approach mathematical modeling of two phase multicomponent transport flow in PEMFC

A quasi two dimensional (1D + 1D), multi-component model is developed in order to analyze the two-phase transport in polymer electrolyte fuel cell. Different operating parameters, including temperature and wettability are examined and their effects are discussed. The present simple and easy to implement model can be as accurate as a complete two dimensional model. Furthermore, it is seen that the simplification made in this model reduce the computational time.

Plasma Actuators for Boundary Layer Control of Next Generation Nozzles

DBD plasma actuators are simple devices comprising two electrodes separated by a dielectric layer. One of the electrodes is covered by the dielectric layer and is completely insulated from the other one, which is exposed to the atmosphere in the top of the dielectric layer. The DBD plasma actuator operates by applying to the two electrodes an high voltage at high frequency from a power supply. When the amplitude of the applied voltage is large enough, in the exposed electrode, an ionization of the air (plasma) occurs over the dielectric surface which, in the presence of the electric field gradient, produces a body force on the ionized air particles. This induces a flow that draws ionized air along the surface of the actuator and it accelerates this neutral air towards downstream, in a direction tangential to the dielectric. Herein we will present this next generation plasma actuator for boundary layer control, which is demonstrated on the acceleration of the flow in a Coanda nozzle wall, thus contributing to help vectoring the exit jet flow. It will be shown that using only the plasma actuator it will be possible to vectorize the exit jet flow even under pure axial flow at the nozzle exit. Experimental results are obtained using flow visualization and Particle Image Velocimetry.Copyright

Exit Flow Vector Control on a Coanda Nozzle Using Dielectric Barrier Discharge Actuator

The paper presents a study on a Coanda nozzle with applications in vectorized propulsion. The nozzle is able to change the exist flow angle as a function of a differential two-stream incoming flow rate. Herein we demonstrate that by using Dielectric Barrier Discharge actuators we are able to extend the range of attainable exit flow angles. First the analysis is performed using a numerical approach; afterwards an experimental facility is implemented to study this same effect. We include a comparison between the experimental testing on the Coanda thruster and CFD computations. Following an analysis of the results we demonstrate that it is possible to achieve a higher exit thrust angle, with the DBD plasma actuators active, and this is shown to be important in order to be able to keep the desired angles under several swirl velocities incoming from the feeding turbofans.© 2014 ASME