FUNDAMENTAL STUDY ON FLOW CONTROL WITH MICRO-ACTUATOR FOR TURBOMACHINE APPLICATION

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This study is a fundamental one to investigate possibility of artificial intellectualization of turbomachines by sensing an abnormal flow condition locally and by controlling the flow automatically by the use of micro-actuators.As a sensing technology, we took up a problem of detection of pre-rotating-stall phenomena, which is the most important problem in abnormal flow conditions in turbomachines. Statistical characteristics of pressure fluctuation on the casing wall of two axial flow compressor rotors and a diagonal flow impeller were investigated experimentally to find a detector or the pre-rotating-stall phenomena. Near stall, the casing wall pressure across a flow passage near the leading edge is characterized by a highly unsteady region where low-momentum fluid accumulates. The periodicity of the pressure fluctuation with blade spacing disappears and an alternative phenomenon comes into existence, which supports the disturbance propagating at a different speed from the rotor revo … More lution. The pre-rotating-stall phenomena can be detected by monitoring collapse of the periodicity in the pressure fluctuation. To represent the periodicity qualitatively, a practical detection parameter was proposed, which is easily obtained from signals of a single pressure sensor installed at an appropriate position on the casing wall during operation of a compressor.As a flow control technology with micro-actuators, effects of micro-excitation of boundary layr on flow conditions around a cylindrical bluff body have been investigated experimentally. The micro-excitation is accomplished by oscillating sidewall surfaces of the body in the cross-flow direction using piezoelectric actuators. The excitation frequency covers below and above a natural vortex shedding frequency from the body and Reynolds number ranges from 5.25*103 to 2.31*104. The excitation of downstream surface of sidewalls affects not much entrainment of vortex shedding frequency. However a substantial amount of entrainment of vortex shedding frequency has been observed by exciting upstream surface of sidewalls where a short laminar separation bubble exists. This is due to delay of boundary layr separation. Less