Abstract
An experimental study of the response of a piezoceramic actuator set at the throat to a transonic diffuser is carried out by measuring wall static pressure fluctuations and by visualizing the flow field using schlieren technique. The visualized flow fields are captured with a digital still camera and a digital high speed video camera. The piezo ceramic actuator is attached at the throat of the diffuser and driven by sinusoidal amplified voltage signals. The diffuser used in this experiment is circular arc half nozzle with the height h* and width w of 3 mm and 25 mm, respectively. The blockage factor of the piezoceramic actuator to the diffuser throat is 9.2% assuring the effect of change in the throat area rather than the boundary layer disturbances. The piezoceramic actuator is driven at the frequency of 100 Hz, 200 Hz, and 300 Hz and its amplitude is about 1 mm. It is found that the wall static pressure fluctuations and the behavior of the shock wave clearly correspond to the vibration of the piezo ceramic actuator for all the frequency ranges whereas the averaged shock position remains almost unchanged. All the results mentioned above suggest that driving the piezo ceramic actuator at the diffuser throat can be one of the promising techniques to control unsteady transonic diffuser flow.
Highlights
The unsteady flow field in a transonic diffuser has attracted a great deal of interest because of the practical industrial importance and because of the complexity of the flow itself
An experimental study of the response of a piezoceramic actuator set at the throat to a transonic diffuser is carried out by measuring wall static pressure fluctuations and by visualizing the flow field using schlieren technique
The blockage factor of the piezoceramic actuator to the diffuser throat is 9.2% assuring the effect of change in the throat area rather than the boundary layer disturbances
Summary
The unsteady flow field in a transonic diffuser has attracted a great deal of interest because of the practical industrial importance and because of the complexity of the flow itself. The approach to stabilize the unsteady flow fields is divided into two major controls, which are active control with jets [4,5] and passive control with a porous cavity [6] or vortex generators. These controls are expected to generate the opposite phase of signals or to retard separations of boundary layers. The causes of the oscillations include pressure disturbances in a core flow and unsteady phenomena associated with the shockboundary layer interaction, as mentioned above, the future trend for the oscillation controls might be a combination of passive and active controls. In the present paper, we focus primarily on the mechanical disturbances by changing cross sectional area at the throat of a transonic diffuser, which is expected to affect the location of shock waves according to the isentropic flow relations between the throat area and local cross sectional area at a location of the shock wave
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