再層流化する乱流境界層における時空間構造の情報量解析

-壁垂直方向の速度差-

抄録

Information analysis of a relaminarizing turbulent boundary layer was investigated. The Shannon entropy, proposed originally for the value of information, utilized to quantify the randomness of the data was applied to the flow field. The turbulent boundary layer was relaminarized by the acceleration due to flow convergence. Fluctuating velocity differences between two points separated in the wall-normal direction in the boundary layer were measured by dual single hot-wire anemometers. The Shannon entropy was obtained from the probabilities of the velocity difference. In addition, permutation entropy based on the ordinal pattern of the data was also obtained. At a certain separation between two points, as the height from the wall increases, the Shannon entropy first increases, reaches a maximum and then decreases. This corresponds to the change in the magnitude of the fluctuating velocity difference. At a certain separation, as the height increases, the permutation entropy increases monotonically, reflecting the richness of the ordinal pattern of the extracted data as the fluctuating velocity difference decreases. As the boundary layer becomes relaminarized downstream, the Shannon entropy decreases due to the decrease in the fluctuating velocity difference. Also, although the qualitative tendency of the permutation entropy does not change, the permutation entropy increases slightly due to the abundance of ordinal patterns in the extracted data.