On the modification of the near-wall coherent structure in a three-dimensional turbulent boundary layer on a free rotating disk

Abstract

An experimental study has been performed on a shear-driven three-dimensional turbulent boundary layer in equilibrium over a rotating disk. The objective of the present study is to investigate the modification of the near-wall coherent structure in the three-dimensional turbulent boundary layer developed in this flow. Two-point velocity measurements are carried out with two X-wire probes which are aligned in the local wall-parallel mean velocity direction, which show that strong asymmetries exist in the velocity cross-correlation coefficient in the spanwise direction, and also in the conditionally averaged velocity signals in the vicinity of a strong ejection or sweep, as was shown by Littell and Eaton [J. Fluid Mech. 266, 175 (1994)]. However, a quadrant analysis reveals that the Reynolds-shear-stress-producing eddies are nearly symmetric in the spanwise direction and those asymmetries are attributed to the changes in the negative-Reynolds-shear-stress-producing motions which have less relation to the streamwise coherent structures. © 1998 American Institute of Physics.