Shintaro Imayama

Pressure fluctuation in high-Reynolds-number turbulent boundary layer: results from experiments and DNS

We have developed a small pressure probe and measured both static pressure and wall pressure simultaneously in turbulent boundary layers up to Reynolds numbers based on the momentum thickness . The measurements were performed at large experimental facilities in Sweden, Australia, and Japan. We find that the measured pressure data are contaminated by the artificial background noise induced by test section and are also affected by the flow boundary conditions. By analyzing data from different wind tunnels acquired at the same Reynolds number, we evaluate the effect of background noises and boundary conditions on the pressure statistics. We also compare the experimental results with results of direct numerical simulations and discuss differences in boundary conditions between real and simulated wind tunnels.

A new way to describe the transition characteristics of a rotating-disk boundary-layer flow

A new method of graphically representing the transition stages of a rotating-disk flow is presented. The probability density function contour map of the fluctuating azimuthal disturbance velocity is used to show the characteristics of the boundary-layer flow over the rotating disk as a function of Reynolds numbers. Compared with the variation of the disturbance amplitude (rms) or spectral distribution, this map more clearly shows the changing flow characteristics through the laminar, transitional, and turbulent regions. This method may also be useful to characterize the different stages in the transition process not only for the rotating-disk flow but also for other flows.

An Experimental Study of a Rotating-Disk Turbulent Boundary-Layer Flow

The azimuthal velocity distribution in a turbulent boundary layer (TBL) on a rotating disk is explored using hot-wire anemometry and compared with those of the two-dimensional TBL over a flat plate.