Turbulent Features in the Coherent Central Region of a Plane Water Jet Issuing Into Quiescent Air

Abstract

A plane water jet issuing into quiescent air at a Reynolds number of 2.5 أ— 105 is experimentally studied using phase Doppler anemometry (PDA). The plane water jet contains a coherent central region, which is situated immediately downstream of the nozzle exit. Particular emphasis is placed upon the distinctive attributes of such a region. Both mean flow pattern and turbulent features are obtained statistically based upon instantaneous velocity data. The central region is overwhelmingly dominated by uniformly distributed velocity, and remarkably high velocity gradient is present near the boundary of this region. Evidence shows that selfpreservation is not satisfied in the central region. Explicit energy dissipation mechanisms in the central region are appreciated from crosssectional uniform distributions of Kolmogorov length scales. Turbulent kinetic energy increases as the plane jet progresses, which is opposite to the general tendency associated with selfpreservation. Although the central region is filled with nearzero Reynolds shear stress, distributions of skewness and flatness in this region are nonGaussian and the instability caused by smallscale flow structures is thereby substantiated.