Structure of Mean Velocity Fluctuation and Its Influence on Turbulence Characteristics in the Entrance Region of a Pipe

抄録

An experimental investigation has been made on the structure of fluctuations of short duration time-mean-velocity, which are primarily due to fluctuations of the turbulent boundary layer thickness, and their effects on the fine structure of turbulence in the entrance region of a pipe. Both the shape of spectrum and the dominating frequency range of mean velocity fluctuations differ markedly from those of the relevant turbulence-velocity component. A slow variation of mean velocity with time induces a similar variation of turbulence intensity over the entire portion of the boundary layer. In the inner layer, the "production effect" caused by mean velocity fluctuations changes the structure of turbulence, while in the outer layer the "convection effect" induced by mean velocity fluctuations governs the overall characteristics of turbulent velocity field.