Recent advancements in PowerMEMS are reviewed. Variety of power generation machine is under development following advances in micro-fabrication technologies. Micro-thermoelectric Generators have advantages in their simple construction, and suit for energy harvesting from waste heat of the internal combustion engines, although the efficiency is low. Micro-fuel cells are recently attracting a lot of research interest, because it is relatively easy to compete against expensive Lithium-Ion batteries in small applications. It is achieving rapid progress, however, it is suffering for variety of problems and the generated power is still low. To achieve both higher power density and energy density, micro-internal combustion engines, such as gas turbines and rotary engines, are under development, however, those are still in a phase of proving the concept. Power MEMS is an emerging technology, which has potential to provide a power for variety of new mobile machines in future.

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Various cavitation instabilities such as rotating cavitation, cavitation surge and etc., have been serious problems in developing high-speed turbopump inducer. In the present study, the attempts to suppress the cavitation surge, which has been observed under partial flow conditions in our helical inducers, are made by installing the obstacle plates just upstream of inducer. Two kinds of obstacle plates were used : one of which is to block the flow axi-asymmetrically and make the inlet distortion, being used to examine the suppressive effects of asymmetric inflow on the cavitation surge. The other is a ring-shaped axi-symmetric plate with blockage of 39% passage near tip region to suppress the growth of inlet back flow under partial flow conditions. In this paper, the effects of suggested obstacle plates on the inducer performances and the occurrence of cavitation surge are discussed through the wall pressure measurements and visual observation of cavity behaviors.

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Two kinds of unstable flows, high/low-speed modes, were observed in a flow system including a mixed-flow vaneless diffuser, and the causes of the unstable flows were experimentally and theoretically researched. The cause of low-speed mode is the mixed-flow vaneless diffuser and the high-speed mode is believed to arise from instability in the inlet pipe system. The effects of physical components of the system were recognized in the measurement of the unstable flow. In the present study, the effects of an inlet pipe, outside diameter of the diffuser and cone angle of the diffuser are examined experimentally. A predicting equation of a rotational speed of cells for low-speed mode is proposed from estimation of measured values, and it is confirmed that the equation is applicable over the wide geometric range of the mixed-flow vaneless diffuser.

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Discrete frequency noise (DFN) induced by rotor-stator interaction has been investigated experimentally. Pressure and velocity fluctuations in the stator passage were also measured to evaluate the correlation with the DFN. Pressure fluctuations on the surface of stator vane do not occur simultaneously in the same phase angle. The pressure fluctuations at leading edge area occur separately from another area. Cross correlation between the DFN and the pressure fluctuations is large, especially Nz and 2Nz. It is concluded from these results that the DFN is dominated by the pressure fluctuations on the pressure side near leading edge.

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