Control of Complex Turbulent Flow

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The ability to manipulate a flow field to change it to the desired form is one of the essential topics in fluid dynamics. Although employing flow control can be seen in different engineering devices, its impact is more significant in the aerodynamics, especially at the low Reynolds number flow regime. The flow pattern may dramatically be reformed by any disturbance in low speed flow and causes a sudden increase of drag and loss of lift and thrust. Therefore, in order to achieve better aerodynamic efficiency, suitable flow control techniques are required in low Reynolds number. Unsteady aerodynamics at a low Reynolds number is a common phenomenon observed in a variety of real-world engineering applications. Typical examples are wind turbines, flying drones, micro aerial vehicles (MAV), small unmanned aerial vehicles (UAV), a flying object operating at low-density atmosphere other than Earth's small-scale lifting surfaces such as insect and bird wings. The combination of small length scale and low velocities results in low Reynolds operating conditions where the viscous effect will cause the unsteady flow separation. The fundamental nature of low Reynolds aerodynamics has enormously rich flow physics, making it an exciting research topic. In this flow regime, the passive flow control cannot improve the aerodynamic performance when the flow changes dramatically. Therefore, active flow control is required to modify the flow pattern in the complex flow conditions. Among different active flow control methods, periodic actuation of the boundary layer has shown a better performance. Smart materials such as Macro Fiber Composites actuators can produce the periodic motion required for aerodynamic performance improvement. Improving science and technology in developing smart materials makes it possible to generate different shapes on the surface (surface morphing) to control the flow pattern. In this research program, the effects of the surface morphing in the form of a traveling wave on controlling the flow separation will be studied by inspiring from aquatic swimmers. The complex flow behavior near the wall region will be investigated. Different mechanisms of exchanging momentum across the boundary layer due to the traveling wave on the surface will be explored. Also, an analytical model will be developed that predicts the optimum surface motion in various working conditions. This model can be used later in the closed-loop control system to adjust the controller. This flow control will be tested numerically on a wind turbine blade to assess its performance to improve the unsteady aerodynamic loads. This program advances our current knowledge in the role of surface morphing on the flow dynamics, which transfers to the development of innovative techniques in developing a new method for controlling the fluid flow. It has significant and broad implications for engineering new tools and technologies from designing smart wind turbines to spy insects.