Rasool Erfani

Influence of shock wave propagation on dielectric barrier discharge plasma actuator performance

Interest in plasma actuators as active flow control devices is growing rapidly due to their lack of mechanical parts, light weight and high response frequency. Although the flow induced by these actuators has received much attention, the effect that the external flow has on the performance of the actuator itself must also be considered, especially the influence of unsteady high-speed flows which are fast becoming a norm in the operating flight envelopes. The primary objective of this study is to examine the characteristics of a dielectric barrier discharge (DBD) plasma actuator when exposed to an unsteady flow generated by a shock tube. This type of flow, which is often used in different studies, contains a range of flow regimes from sudden pressure and density changes to relatively uniform high-speed flow regions. A small circular shock tube is employed along with the schlieren photography technique to visualize the flow. The voltage and current traces of the plasma actuator are monitored throughout, and using the well-established shock tube theory the change in the actuator characteristics are related to the physical processes which occur inside the shock tube. The results show that not only is the shear layer outside of the shock tube affected by the plasma but the passage of the shock front and high-speed flow behind it also greatly influences the properties of the plasma.

The Influence of Electrode Configuration and Dielectric Temperature on Plasma Actuator Performance

In this paper further experimental studies have been conducted for a new con guration of the Multiple Encapsulated Electrodes (MEE) actuator. The MEE actuator consists of an encapsulated electrode split into smaller electrodes and distributed through the dielectric. This type of actuator has been shown previously to produce performance superior to the standard actuator design. This makes them more desirable as ow control devices. Using particle image velocimetry to visualize and quantify the ow eld, the new con guration has been applied individually and in pairs, and compared to another MEE con guration and the standard design. The results show that further manipulation of the encapsulated electrode can improve performance when compared to other MEE designs. The actuators have also been operated under three di erent surface temperature conditions. Operating the actuator at lower temperatures provided improved performance by increasing the induced velocity while lowering the power consumption.

Multiple Encapsulated Electrode Plasma Actuators to Influence the Induced Velocity: Further Configurations

Further configurations of the Multiple Encapsulated Electrode plasma actuators have been investigated. The actuators consist of 2 encapsulated electrodes distributed throughout the dielectric layer to influence the electric field distribution. The velocity fields have been recorded using PIV in a quiescent environment. Various velocity profiles have been extracted and used to compare the performance of the different configurations. The voltage and current characteristics, from which the power can be calculated, has also been recorded. The plasma is seen to couple momentum into the quiescent environment with the amount of coupling being influenced by the electrode configurations. The highest induced velocity achieved was 91.2% greater than the baseline case while using only 26.2% more power, at the same input voltage.

Plasma Actuators with Multiple Encapsulated Electrodes to Influence the Induced Velocity

A new configuration of plasma actuator, that uses multiple encapsulated electrodes has been compared to a corresponding standard configuration. The velocity fields generated have been recorded using PIV and the voltages and currents recorded. It has been shown that the encapsulated electrode affects the induced jet characteristics. The position to the initial jet has been manipulated as has the initial jet thickness. Velocity is seen to increase linearly along the encapsulated electrode, while momentum coupling has been achieved 15mm downstream of the encapsulated electrode. The magnitude of the induced velocity was also affected with all of the multiple encapsulated electrode actuators producing induced velocities greater than the baseline case. The highest induced velocity was 36.5% greater than the baseline case at the same input voltage while requiring 11.7% less power.

An evolutionary approach to solve a system of multiple interrelated agent problems

Graphical abstractDisplay Omitted HighlightsWe develop an evolutionary approach to solve interrelated optimisation problems.Multiple agents autonomously deal with their own problems and react to the others.Test problems in water pollution and aerospace modelling demonstrate the algorithm.Experiments on scalability and convergence of the algorithm show promising results. Deterministic approaches to simultaneously solve different interrelated optimisation problems lead to a general class of nonlinear complementarity problem (NCP). Due to differentiability and convexity requirements of the problems, sophisticated algorithms are introduced in literature. This paper develops an evolutionary algorithm to solve the NCPs. The proposed approach is a parallel search in which multiple populations representing different agents evolve simultaneously whilst in contact with each other. In this context, each agent autonomously solves its optimisation programme while sharing its decisions with the neighbouring agents and, hence, it affects their actions. The framework is applied to an environmental and an aerospace application where the obtained results are compared with those found in literature. The convergence and scalability of the approach is tested and its search algorithm performance is analysed. Results encourage the application of such an evolutionary based algorithm for complementarity problems and future work should investigate its development as well as its performance improvements.

Fair Resource Allocation Using Multi-population Evolutionary Algorithm

Resource allocation between selfish agents are performed under centralised and/or distributed mechanisms. However, there are issues in both cases. In centralised solution, although the resources are allocated in an efficient way, the allocation decisions may not be acceptable for some selfish agents making them reluctant to cooperation. In decentralised solution, although the problem is solved from each agent’s perspective, the allocation leads to an inefficient usage of provided resources. For example, such an issue is evident in a water network distribution system where different agents share the river water and a central planner (CP) maximises the social welfare to the whole system. Issue arises when the CP solution is not acceptable by some agents. Therefore, a mechanism should be devised to encourage each agent to accept the CP decision. This paper introduces a mechanism in re-distributing the CP revenue value amongst the competing agents based on their contribution to the CP value. To find each user’s contribution, this paper develops a parallel evolutionary search algorithm which enables the agents to autonomously solve their local optimisation problem whilst interacting with the other agents and the whole system. The search evolves towards a solution which is used as an incentive for calculating a fair revenue for each agent. The framework is applied to a river reach with five competitive users. Results show decentralised coupled centralised approaches has the potential to represent mechanisms for a fair resource allocation among competing self-interested agents.

Flow Control of a NACA0015 Airfoil in a Turbulent Wake Using Plasma Actuators

This work involves the control of leading edge ow separation occurring over an aerofoil at high angle of attack. It also contains the documentation of boundary layer transition from the laminar to the turbulent state over an aerofoil facing the wake of circular cylinder. A symmetric NACA 0015 aerofoil was used because of its well documented stall properties. Surface pressure measurement was used to determine the lift coe cient. Mean velocity pro les of the wake of the aerofoil were used for drag coe cient calculation. The experiment was carried on in the chord Reynolds number of 1:5 10. A Multiple Encapsulated Electrode (MEE) plasma actuator was embedded at the leading edge of the aerofoil. It was found that it can delay separation and increase the stall angle. It was accompanied by improvement of the aerodynamic coe cient of aerofoil facing the wake.

Optimization of Induced Velocity for Plasma Actuator with Multiple Encapsulated Electrodes using Response Surface Methodology

In design problem such as a new configuration of plasma actuator for maximizing the velocity of the airflow, experimental setup is done by an ad-hoc procedure. This provides the researcher with a relationship of the input parameters (width of the electrode, distance of the electrodes, the voltage and etc) and the velocity. As the experiments are time consuming and expensive in most of the cases, the above method is not always a reasonable approach in finding the optimal plasma configuration. In this paper response surface methodology, a surrogate modelling approach, is used to allow a systematic investigation in setting the experiments and finding the optimal plasma configuration. This allows the researcher to consider the uncertainty in observation and find a reliable approximate model for the induced velocity. Furthermore, the velocity of the airflow is modelled with small while enough number of experimental setups. The model is validated with the experimental data.

Approximation of the pareto surface via a hybrid of scalarization method and evolutionary algorithm

© 2015, American Institute of Aeronautics and Astronautics Inc. All Rights Reserved.In engineering design process, multiobjective optimization plays an important role. Since the solution to the problem is not unique, the designer requires a set of evenly distributed solutions for trade-off analysis. Classical gradient based algorithms and evo- lutionary approaches have shown their capability on producing such a set. This paper introduces a hybrid method which exploits a classical scalarization approach to partition the solution space into different and distinct local search spaces. The sub-problems in each local search domain are then solved by evolutionary strategies in parallel by using the neighboring population information. The fitness function is constructed to handle the problem constraints and meanwhile minimize the distance of the solution to the true opti- mum frontier. The algorithm behavior is studied on different numerical test cases as well as an engineering aerodynamic problem. The results are compared in both convergence and diversity to those of another well known approach to demonstrate the efficacy of the proposed method. It is concluded that scalarization increases the convergence speed while maintaining a well spread set of solutions.

Multiple encapsulated electrode plasma actuator effect on aerofoil-wake interaction

Dielectric barrier discharge (DBD) plasma actuators have received considerable attention by many researchers for various flow control applications. Having no moving parts, being light-weight, easily manufacturable, and their ability to respond almost instantly are amongst the advantages which has made them a popular flow control device especially for application on aircraft wings. The new configuration of DBDs which uses multiple encapsulated electrodes (MEE) has been shown to produce a superior and more desirable performance over the standard actuator design. The objective of the current study is to examine the effect of this new actuator configuration on the aerodynamic performance of an aerofoil under wake interaction conditions. The plasma actuator is placed at the leading edge of a symmetric NACA 0015 aerofoil which corresponds to the location of the leading edge slat. The aerofoil is operated in a chord Reynolds number of 0.2×10. Surface pressure measurements along with the mean velocity profile of the wake using pitot measurements are used to determine the lift and drag coefficients, respectively. The results show an increase in the lift coefficient. It is also demonstrated that the drag coefficient decreases at all the measured angles of attacks.