Yu Nishio

Two-dimensional numerical simulation is carried out to investigate the leading edge receptivity of a at-plate boundary layer. It is shown that velocity fluctuations inside the boundary layer at an elliptic leading edge is suppressed by changing the local viscosity limited to velocity fluctuations. The amplitude of the velocity fluctuation in the boundary layer increases rapidly right after the junction between the elliptic leading edge and the at plate, which also depends on the frequency of the vortical disturbances given upstream.

Wind tunnel experiment is carried out to investigate the noise suppression effect of a small bump on the cavity bottom floor. The bump is placed 60% of the cavity length away from the upstream edge of the cavity. The results show that the noise suppression effect is large when the geometry of the obstacle is closer to a least-complicated two-dimensional rectangular cylinder.

Behavior of a droplet on a vibrating plate is simulated by an incompressible SPH method with a surface tension model based on the inter-particle attraction. Vibrating frequency is chosen so that the surface deformation of the droplet will become the maximum. As a result, it is shown that the mixing inside a droplet is enhanced by vibrating the plate.

A fl w on the circumferential side of a rotating disk is investigated experimentally. Through hot-wire measurement and smoke visualization, it is shown that the fl w on the circumferential side is sensitive to the existence of rotating shaft.

Unsteady torque generated on a straight-bladed vertical axis wind turbine with two blades is investigated by wind tunnel experiment and a two-dimensional numerical simulation. The experimental result shows that instantaneous torque takes a positive value when the blade passes through the second and the fourth quadrants in the rotating plane. The numerical result indicate that this is due to the transient increase of the effective angle of attack in this regions.

Three-dimensional boundary layer flow over a rotating disk is studied by a numerical method. A disturbance is introduced into the laminar flow from the wall at a location where the Reynolds number is higher than the critical value to maintain a turbulent state. As a result, it is found that the disturbance grows up to spiral vortices, which are aligned regularly in the circumferential direction, and then, finally turns into a turbulent flow, which is similar to a conventional transition process initiated from the low Reynolds number location.

Feedforward control to suppress the instability waves whose frequency changed periodically is attempted in a wind tunnel experiment of a fla plate boundary layer. It is shown that the control effect can be improved by taking into account the dispersibility of the target instability waves.

Numerical simulations are carried out to find out the optimum operating mode of a piezo-ceramic actuator attached to a flat-plate surface. The goal is to generate a strong velocity fluctuation waves in a boundary layer. As a result, it is shown that strong waves can be generated when the actuator is operated concentrating the production of vorticity fluctuations to smaller region. It is also shown that making the actuators to travel downstream at the speed of the target T-S waves can generate even stronger waves.

Three-dimensional numerical simulation is carried out to investigate the onset of turbulence in a bypass transition. Short duration jet is ejected into a low-speed streak and their growth is simulated. As a result, it is shown that the onset of turbulence appears as a when the number of strong vortices start to increase, which is a little later than when the effective vortex stretching starts to increase.

Turbulent drag reduction over riblets with trapezoidal cross-section was examined by wind channel experiment and direct numerical simulation. The maximum drag reduction of 6% compared to the smooth surface was confirmed for the straight groove with spanwise interval of 18 in wall units. The good agreement between experiment and DNS was demonstrated. Drag reduction over wavy riblets was also examined.

A relation between the vorticity disturbances and the leading edge receptivity is investigated numerically. Freestream disturbances are given as a two-dimensional periodic vorticity fluctuation at the upstream boundary. Three cases changing the height of the impinging vortices are tested. The result shows that location of the impinging vorticity pattern influence the vorticity pattern near the wall of the boundary layer, changing the receptivity.

Streamwise vortices in a three-dimensional boundary layer were used to the separation control. The three-dimensional boundary layer was generated on a flat plate with yawed displacement upper body. A separation region was generated by small obstacles. The velocity profiles behind obstacles were measured by using a hotwire anemometer. As a result, streamwise vortices effectively recovered the velocity of the separation region when the pressure gradient was steep.