Sei-ichi Iida

Coherent Structures in a Three-Dimensional Wall Jet

The formation mechanism of streamwise vortices in the near field of the three-dimensional wall jet discharging from a circular nozzle along a flat plate is studied experimentally using a conditional sampling technique. Ensemble-averages of the lateral velocity component indicate the presence of large-scale horseshoe-like structures, whose legs are inclined and stretched to form the streamwise vortices in the mixing region of the jet. Based on the present result, a coherent structure model for the near field of the wall jet is proposed.

Behavior of turbulence in the near wake of a thin flat plate at low Reynolds numbers

Conventional hot‐wire measurements have been made in the turbulent developing wake of a thin flat plate. The data obtained are primarily concerned with turbulence characteristics in the near‐wake region. Turbulence properties in the inner wake first increase up to a streamwise distance of 200–300 times the initial wall‐layer length scale, followed by a gradual decay farther downstream. The mechanism of this overshoot phenomenon is inferred from space‐time correlation data. Quasiperiodic motion similar to that in the far wake is observed as early as near the end of the near wake.

The Particle Tracking Method Using the Kalman Filter

An alternative particle tracking method for PIV (Particle Imaging Velocimetry) was developed by applying the Kaiman filter. Numerical simulations to track particles in a 2-D cavity flow were performed to investigate the effects of the present method. It was proved that the method can considerably improve the accuracy and the dynamic range of the PIV measurement.

The near field of a fully turbulent circular jet

The near‐field measurement of fully turbulent jets discharged from a straight circular pipe indicates the presence of quasiperiodic velocity perturbations. The Strouhal number based on the predominant frequency falls in the range of the preferred mode for the jet with a potential core and has an asymptotic value of 0.38 in the high Reynolds number regime. Regular perturbations are not observed in the mixing region immediately downstream from the pipe exit.

Stochastic Turbulent Diffusion Model Considering Space Correlation.

A stochastic model which is used for simulating the time evolution of material line stretching in homogeneous turbulence is developed. Although the present model is similar to the Lagrangian random flight model, turbulent velocity is calculated for the Eulerian grid points considering space correlation in addition to time correlation. Scales of turbulence are estimated from turbulent energy (k) and dissipation rate (e). Deformation of material line in two-dimensional homogeneous turbulence is simulated by using this model and the result shows that spatial scale of turbulence affects on the distortion of material line.