|M.Sc Student||Romm Iliya|
|Subject||Subcritical Pipe Flow Transition Control Using Dielectric|
Barrier Discharge Plasma Actuators
|Department||Department of Mechanical Engineering||Supervisor||PROF. David Greenblatt|
|Full Thesis text|
Dielectric barrier discharge (DBD) plasma actuators have been used increasingly in recent years for active flow control (AFC) in gasses such as air and presently they dominate this area of research. While much work was done in external flows, such as the flow over airfoils and bluff bodies, no work has been done in internal flows, such as those in circular pipes and channels. This work details the application of DBD actuators to the control of transition in subcritical Reynolds number (250 ≤ Re ≤ 1000) circular pipe flows for the purposes of increasing mixing and momentum/heat transfer. Primary flow measurements were made using a single hot-wire anemometer and these were augmented using smoke filament visualization with high-speed photography. A sensitive balance was used to calibrate the momentum (force) generated by the actuator as a function of input power. The actuator introduces a body force into the boundary layer of the flow, thus generating a local instability and triggering intermittent transition to turbulence. Several distinct actuator configurations were considered and a down-selection indicated that the introduction of swirl produced the largest coherent oscillations and purely turbulent fluctuations. Using the swirl actuator, a detailed parametric study was conducted where operation parameters (such as: duty cycle, input power, frequency, momentum, etc.) were systematically varied. Dimensional analysis indicated that the largest coherent disturbances occur at a reduced frequency of ~0.08 while peak turbulence levels occur around 0.34. High-speed flow visualization indicated a complex three-dimensional flow structure within the actuated flow regime, with regions of localized reverse flow. Several diameters downstream, however, the flow became essentially axi-symmetric in a phase-averaged sense and a fairly simple model could be used to describe the basic mechanisms. The principles found in this research can be applied to similar systems operating with other fluids, such as weakly conducting liquids used in conjunction with Lorentz force actuators.