Plasma actuators have shown their ability for different applications within the active flow control and heat transfer fields. These simple devices are inexpensive, present robustness, low weight and are fully electronic. However, they still present some debilities in terms of durability and maximum induced flow velocity. To overcome these issues, during the last years, a few different configurations of dielectric barrier discharge plasma actuators have been proposed but, always making use of dielectric barrier discharge layers of constant thickness. For the first time, the present study herein introduces a new plasma actuator configuration that makes use of a stair-shaped dielectric layer, which aims to increase the induced flow velocity and improve the mechanical efficiency without compromising the durability of the device. In this new concept, instead of using a dielectric layer with constant thickness, the thickness of the dielectric layer decreases along the covered electrode width, which leads to an increase of the plasma discharge extension and an increase of the maximum induced flow velocity. Several actuators based on a stair-shaped dielectric layer were experimentally tested and compared with the conventional actuators. The results demonstrated that the stair-shaped actuators allow us to obtain a plasma discharge longer. It was found that by implementing a stair-shaped dielectric layer with a slope angle, in a 1.92 mm thickness actuator, it is possible to increase the maximum induced flow velocity in about 32% by consuming 36% less power. These results lead to a mechanical efficiency five times bigger than the obtained with conventional constant thickness actuators.

In the present study, two dimensional flow over a backward-facing step in laminar flow regime with application of active flow control (AFC) technique is analysed. The aim of the present work is to gauge the effectiveness of implementing AFC to reduce drag and study its effects on flow characteristics. In order to analyse the influence of AFC on the boundary layer and the downstream vortex shedding, two different kinds of AFC techniques have been used in this study namely zero net mass flow actuators and fluidic actuators. A parametric non dimensional analysis has been carried out by varying the frequency from 0.025 to 0.1 and jet amplitude from 0.05 and 1. Four different positions of the groove were simulated; groove was respectively located at 0.024a, 0.047a, 0.072a and 0.097a, measured upstream from the right side upper edge. Three different non dimensional groove widths 0.023a, 0.048a and 0.073a were also evaluated, where a is the step height. The idea behind this study was to determine an optimal configuration to reduce the drag on the step and to suppress the vortex dissipation in the wake of the step. It was observed that when using an AFC frequency ± 10% of the vortex shedding one, was causing the maximum drag reduction. When comparing the effects of zero net mass flow actuators with the fluidic actuators, it was observed that zero net mass flow actuators were more effective.