|M.Sc Student||Elatov David|
|Subject||Separation Control in a Centrifugal Fan Using|
|Department||Department of Mechanical Engineering||Supervisor||Professor David Greenblatt|
|Full Thesis text|
Centrifugal blowers are turbo-machines in which air enters in the axial direction. After being diverted to flow in the radial direction along the impeller blades, the air discharges from the outer circumference, to the blower housing and exits the blower. The blowers are classified by the curve of their blades relative to the direction of rotation, namely forward curved, backward curved and straight bladed.
Recent surveys show that approximately 20% of the industrial power consumed in the US and EU is channeled to the operation of industrial fans and blowers. However, in certain regimes of operation, the otherwise smooth airflow over the blades detaches - a phenomenon known as stall - causing a pressure drop, efficiency losses, noise, and potentially harmful vibrations. Despite the fact that flow control, both active and passive, has been proven to improve the performance of airfoils subjected to uniform flow, very little research was conducted regarding flow control over centrifugal and axial impellers. The stalled regime is, therefore, generally avoided rather than dealt with.
Dielectric Barrier Discharge plasma actuators are a simple, elegant, and robust way of implementing active flow control. These actuators consist of two thin electrodes, separated by a dielectric material. Implementing high voltage between both electrodes creates a strong electric field that ionizes the ambient air, creating plasma. Activating the plasma in pulsed mode can harness the instabilities observed in stalled flow, causing the downstream flow entrainment, thus attaching the separated flow. Another method of operation is activating the plasma in a non-pulsed mode, causing it to produce a flow similar to that of a steady jet.
In order to conduct the research, an experimental apparatus for passive and active flow control was designed and constructed using the housing of a 0.5 kW industrial blower in which the 3D printed designed experimental impellers were installed and tested.
Using different actuators and actuation locations, up to 10% improvement was achieved. Moreover, the power required to drive the actuators varied significantly for different actuator configurations. Based on a comparison with the squirrel cage blowers, it was concluded that conventional stall was not observed on the blades. Furthermore, high speed footage of tufts over the blades had shown poor aerodynamic performance. A basic theory was developed to explain the effect of the jet flap actuator and the results corresponded well with experimental data.