Forefront of Wind-Tunnel Experiment on Turbulence Structure

Abstract

Many interesting and important basic problems still remain unsolved or ever untouched in the fields of experimental fluid dynamics. The present report explains a variety of newest results of wind tunnel experiments conducted chiefly in our laboratory with respect to the features of large scale quasi-isotropic turbulence, anisotropic turbulence, three-dimensional vortical structure in the wake of a sphere, the process of vortex pairing in a two-dimensional jet, the proposal for a new model on a boundary layer transition in a view point of hairpin or horse-shoe vortex and lastly the analysis on spontaneously generated internal gravity waves in a stably stratified mixing layer. These results, the author guesses, will promise the future possibility in the fields of experimental fluid dynamics.

Flow Visualization of Spinning and Nonspinning Soccer Balls Using Computational Fluid Dynamics

“…Sci. 2020, 10, x FOR PEER REVIEW 11 of 15 [14][15][16][17]. In addition, a large-scale vortex pair has been observed in wind tunnel tests conducted on nonspinning baseballs [10] and soccer balls [43].…”

“…Various vortex structures containing a large-scale counter-rotating vortex have been observed in the wake of a smooth sphere, such as a horseshoe vortex, an alternating vortex, or a hairpin vortex [14][15][16][17]. In addition, a large-scale vortex pair has been observed in wind tunnel tests conducted on nonspinning baseballs [10] and soccer balls [43].…”

“…However, relatively few studies have examined the air flow around a ball and the vortex structure and dynamics that generate these aerodynamic characteristics [10,11], although analysis of the vortex structure and dynamics is very important to elucidate the fundamental aerodynamics of sports balls. Many studies have previously been conducted on the vortex structure of a smooth sphere [12][13][14], and the results indicate that a horseshoe vortex, an alternating vortex, or a helical vortex is formed depending on the Reynolds number [15][16][17][18]. However, numerous aspects regarding the formation and transition mechanisms of vortex structures are still unknown.…”