208 二方程式乱流モデルを適用した共存対流乱流輸送機構の考察

Abstract

Recently, the two-equation turbulence models for simulating velocity fields have been improved variously. It becomes possible that the turbulence models accurately estimate turbulent statistic such as Reynolds stress near wall and the wall asymptotic behavior. The two-equation turbulence models have also been developed on temperature fields, and the models are useful for simulating another turbulent statistic such as turbulent heat fluxes near wall. However, the turbulent combined convection strongly affected by buoyancy, there is little research effort in which an appropriate turbulence model is made to reflect the buoyant effect accurately. In general, it is often difficult to measure the turbulent statistic of the combined convection at a good accuracy, because the influence of temperature fluctuation on various sensors is rather large. Analyzing the turbulent transport phenomena strongly affected by the buoyancy has not even been discussed empirically owing to the difficulty of the measurement. In particular, the behavior of the turbulent Prandtl number has not been addressed numerically and empirically for the buoyant dominant flow such as the combined convection. Therefore, in this study, the buoyant components were introduced to the turbulent fluxes such as Reynolds stress and turbulent heat fluxes; the turbulent transport phenomena of the combined convection were modeled by adding several buoyant-induced components to the expressions of the turbulent fluxes. The turbulent transport mechanism of the combined convection was also examined by applying a new damping function being applicable to both the aiding and the opposing flows. The calculation target is the fully-developed turbulent combined convection between vertical smooth parallel plates, where the inertia force acts on parallel or opposite to the buoyant force. The wall is heated uniformly. The numerical computation was performed by combining the two-equation turbulence models of the different type being applicable to both the velocity and the temperature fields. It was revealed from a series of computations that the utilized model simulates the heat transfer and fluid flow of the turbulent combined convection physically. Confirming the applicability of the two-equation turbulence models to the turbulent combined convection is important. Realizing the industrial convenience by using more appropriate and simpler turbulence models with the aid of the empirical knowledge is also necessary.