バックステップを過ぎる粘弾性流体乱流の空間相関関数による解析

抄録

In this paper, we carried out experiments on backward-facing step (BFS) turbulent flow to investigate viscoelastic influence. We performed particle image velocimetry (PIV) measurement on turbulent flow passing BFS for Newtonian and viscoelastic fluids. The measurement fields were set in x-y plane and x-z plane (here, x is streamwise direction, y is wall-normal direction and z is spanwise direction). The instantaneous velocity fields show that meandering main flow in x-y plane (not in x-z plane) on certain conditions. We employed analysis to investigate characteristics of turbulent structure using of method combined with 4-quadrant classification method and two-point correlation function. The results show that meandering motion is dominated varicose mode, vortices are generated from shear layer, accompanied with that low speed fluid ejecting from upper wall. High correlation region of streamwise velocity fluctuation corresponding to meandering motion is observed at inflection point of streamwise velocity.