Experiments on the growth of the Large-scale Structures in a Reciprocating Oscillatory Flow

Abstract

Oscillatory turbulent shear flows are frequently encountered in the field of hydraulics, such as river flows in tidal estuaries, surging motion of water columns in a penstock and a surge tank of a hydroelectric power station, wave motions on a bottom. The large-scale structures of a reciprocating oscillatory turbulent flow in a rectangular duct is investigated experimentally by multiple-probe hot-wire rakes. Using conditional sampling technique, we have found that the large-scale structures is a pair of counter-rotating fluid motion. These structures grow explosively at the beginnig of flow deceleration and produce high Reynolds stress. The character of individual structure is found to be very similar to that of the ensemble averaged structure.