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A large-eddy simulation has been performed to study the temporal and spatial dynamics of a rotor tip-clearance flow, with the objective of determining the underlying mechanisms for low pressure fluctuations downstream of the tip-gap. Simulation results are compared with experimental measurements, and favorable agreements are observed in both qualitative and quantitative sense. Typical vortical structures such as the tip-leakage vortex and tip-separation vortices are revealed, and their evolution is shown to be strongly influenced by the moving endwall and the blade wake. These vortical structures are the main sources of turbulence energy and Reynolds stresses as well as low-pressure fluctuations. Cavitation-inception analysis shows a high correlation between cavitation and the tip-leakage vortex.

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A compact dual-circinal rectenna with omnidirectional characteristic is designed for microwave wireless power transmission at 2.45 GHz. A novel dual-circinal receiving antenna with the reflection coefficient of −32.5 dB is proposed which is formed by expanding folded curves. By designing an impedance matching network with a 60 radial stub and a single stub, a rectifier is presented with the maximum efficiency of 55.6 % and the output dc voltage of 1.19 V under the input power of 0 dBm. Simulation and measurements have been carried out for the antenna and the rectifier. The measured results agree well with the simulated value. The results of rectenna experiment show that the maximum conversion efficiency is 51% at 2.45 GHz when the input power is 0 dBm. The proposed rectenna has the characteristics of compact size and omnidirectional harvesting which are advantageous in RF energy harvesting applications. K E Y W O R D S 2.45 GHz, compact, dual-circinal rectenna, omnidirectional, wireless power transfer

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