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Handa T.,Kyushu University | Mii K.,Kyushu University | Sakurai T.,Kyushu University | Imamura K.,Nippon Steel and Sumikin Engineering | And 2 more authors.
Experiments in Fluids | Year: 2014

In the present study, the characteristics of supersonic rectangular microjets are investigated experimentally using molecular tagging velocimetry. The jets are discharged from a convergent-divergent rectangular nozzle whose exit height is 500 μm. The jet Mach number is set to 2.0 for all tested jets, and the Reynolds number Re is altered from 154 to 5,560 by changing the stagnation pressure. The experimental results reveal that jet velocity decays principally due to abrupt jet spreading caused by jet instability for relatively high Reynolds numbers (Re > ~450). The results also reveal that the jet rapidly decelerates to a subsonic speed near the nozzle exit for a low Reynolds number (Re = 154), although the jet does not spread abruptly; i.e., a transition in velocity decay processes occurs as the Reynolds number decreases. A supersonic core length is estimated from the streamwise distribution of the centerline velocity, and the length is then normalized by the nozzle exit height and plotted against the Reynolds number. As a result, it is found that the normalized supersonic core length attains a maximum value at a certain Reynolds number near which the transition in the velocity decay process occurs. © 2014 Springer-Verlag Berlin Heidelberg. Source


Yamaguchl T.,University of Kitakyushu | Katsura T.,Hokkaido University | Nakamura Y.,Nippon Steel and Sumikin Engineering
Journal of Environmental Engineering (Japan) | Year: 2014

The authors established a technique for measuring heating or cooling output from a heat pump air conditioning system by applying the refrigerant enthalpy method. In this paper, advantages of the technique and estimation process of the heating or cooling output are introduced. In addition, field experiment with a water source heat pump unit was carried out to validate the established technique. In the experiment, the refrigerant saturation temperatures at inlet and outlet of compressor and compressor frequency, which are estimated in the technique, are firstly verified by comparing to measured values. As the result of experiments, it is confirmed that the established technique have possibility of omitting foundation of the pressure sensors and the measurement of compressor's frequency in the technique. As the another results of experiments, the error of estimation values of heat quantity between the established technique and the conventional one is less than 5 % for cooling and 7 % for heating. Therefore, the technique for heat quantity measuring that the authors established has the potential to become the new measuring method for the heat pump air conditioning system. Source


Yamaguchi T.,Nikken Sekkei Ltd. | Katsura T.,Hokkaido University | Nakamura Y.,Nippon Steel and Sumikin Engineering
Journal of Environmental Engineering (Japan) | Year: 2015

The authors established a technique for measuring calorie output from a variable refrigerant flow air conditioning system by applying the refrigerant enthalpy method. In this paper, the advantages of the measuring technique and its detailed estimation process of the calorie output are introduced. In addition, the measurement with water cooled variable refrigerant flow air conditioning system was carried out in order to confirm the accuracy of technique. In this actual measurement, it was shown that measuring the appropriate pressure of refrigerant in the heat pump is important to achieve the measurement accuracy. As the another results of actual measurement, the error of estimation values of heat quantity between the established technique and the conventional one is less than 20 % for cooling and heating, respectively. Therefore, the technique for measuring calorie output that the authors established has the high measurement accuracy. In addition, the authors suggested operation improvement method by analyzing measured values such as pressure, calorie output, electric power consumption and so on. As the results, it was confirmed that COPs is improved in the cooling period by lowering the high side pressure of refrigerant in the heat pump depending on the inlet water temperature in the primary side of the pump. Source


Suzuki H.,University of Tokyo | Shibata H.,University of Tokyo | Fujioka H.,Nippon Steel and Sumikin Engineering | Hirabayashi S.,University of Tokyo | And 2 more authors.
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2013

Coupled rotor-floater response analysis is essentially important for the design of Rotor Nacelle Assembly (RNA) and floating support structure of Floating Offshore Wind Turbine (FOWT). The authors have developed an analysis code UTWind for analysis of the coupled structural response. Blades and floater are modeled as frame structure with beam elements. Lumped mass model is use for mooring. Aerodynamic load on blade is calculated by Blade Element Momentum Theory (BEM), and hydrodynamic load is calculated by Hooft's method, and Morison equation was modified to be applicable to cylindrical element with cross section with two axes of lines symmetry. The equations of motion of rotor, floater and mooring are solved in time domain by weak coupling algorithm. The numerical results by the code were compared with responses measured by experiment in wave and wind-and-wave coexistence field with/without blade pitch control and showed good agreement. Response by negative damping was reproduced by the code and showed good agreement with experiments. © 2013 by ASME. Source


Handa T.,Kyushu University | Miyachi H.,Mitsubishi Group | Kakuno H.,Nippon Steel and Sumikin Engineering | Ozaki T.,Kyushu University
Experiments in Fluids | Year: 2012

The mechanism behind cavity-induced pressure oscillations in supersonic flows past a deep rectangular cavity is not well understood despite several investigations having been carried out. In particular, the process by which the pressure wave is generated and the path of the pressure wave propagating inside the cavity remains unclear. In the present study, the pressure waves around a deep rectangular cavity over which nitrogen gas flows at a Mach number of 1.7 are visualized using the schlieren method. The length of the cavity is 14.0 mm. The depths of the cavity are selected as 20.0 and 11.7 mm, corresponding to length-to-depth ratios of 0.70 and 1.2, respectively. The pressure waves propagating inside as well as outside the cavity have been successfully visualized using a high-speed camera, and the propagation pattern of these waves is found to be different from that previously predicted by numerical simulation and from those expected in previous oscillation models. In addition, the pressure oscillation near the trailing edge of the cavity is also measured using semiconductor-type pressure transducers simultaneously with the capture of the schlieren images. As a result, the relationship between the shear-layer motion, pressure-wave generation, and pressure oscillation at the trailing edge of the cavity is clarified experimentally. © 2012 Springer-Verlag Berlin Heidelberg. Source

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