| Research Abstract |
At first, Local Dynamic similarity model giving special notice on dynamic similarity of cross-ventilation was applied to the outflow openings. Cross-ventilation performance at the openings on outflow side was evaluated, and the structure of air flows around the outflow openings was studied by LES and wind tunnel experiment. It was found that LES reproduces the results of the wind tunnel experiment fairly well such as extensive increase of discharge coefficient in a small region where P_R^* value is low. The evaluation of the pressure field by LES revealed that the remainder of dynamic pressure in the air flows and the change of pressure field around the outflow openings give strong influence on discharge coefficient. Also, by identifying the configuration of the stream tube of ventilation air flow, it was found that discharge coefficient is changed depending on how the air flows go out. In general, dynamic pressure tangential to wall surface at the outflow openings is considered to be
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lower than that of the inflow side. The frequency of occurrence of P_R^* was investigated by actual-size experiment, and it was elucidated that the region of P_R^* where discharge coefficient is extensively decreased develops only very rarely.
In the second place, to evaluate wind pressure distribution on a building by using CFD (computational fluid dynamics), it has been generally practiced to use k-ε models. However, it is known that the use of the standard k-ε model has disadvantages such as overestimation of wind pressure coefficient and turbulent kinetic energy on the windward surface where wind impinges on the building. To overcome these problems, various modifications of the k-ε model have been proposed. In the present study, a number of modified k-ε models and k-ω model were applied for the estimation of wind pressure distribution on the building, which was designed in parallelepiped shape, and the characteristics in each of these models were confirmed. The results of the present study suggest that the modified k-ε model incorporating Durbin's limiter (model parameter α=0.5) showed satisfactory results for the estimation of wind pressure distribution. In the overall evaluation, the modified k-ε models (incorporating Durbin's limiter (α=0.65), RNG model (renormalization group theory) and Quadratic model) provided good results.
At the last, cooling load reduction by introducing cross-ventilation is estimated trough use of building simulation program, TRNSYS with COMIS. Results show the load reduction depends on the building characteristics and way of windows operation. Generally, lower reference temperature, i.e. higher internal heat gain, and lower heat loss coefficient, brings higher load reduction. Larger amount of building thermal capacity also associates the effect. For windows operation, several ways of operations are tested and compared. The reduction rate varies from 10 to 20 % for wooden detached house in suburban area in Japan, depending the way of windows operation. The cooling load is not drastically reduced solely by opening windows during occupied and waking period. Frequent window operations sensitive to ambient conditions especially during night and unoccupied period increase the effect of cross-ventilation. Less
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