Simulation of Instability Development in a Plane Submerged Jet at Low Reynolds Numbers

Abstract

Numerical simulation of a plane submerged jet with Reynolds number of 32 ≤ Re ≤ 160 based on the mean inlet velocity and the flat slit height at the jet entrance is performed using the continuity and Navier - Stokes equations for incompressible fluid. The influence of changes in Re on the flow nature is studied with assignment of small random perturbations at the jet inlet and in the absence of these perturbations. In agreement with the available data of laboratory experiments, the present computation results show the laminar flow state in the first region near the exit from the slit, the asymmetric instability of sinusoidal type in the second, transitional region, and the irregular, turbulent nature of the flow in the third region. It is found that the lengths of the first and second sections decrease with increasing amplitude of small random perturbations introduced by distortion of the inlet velocity profile. Moreover, an increase in the Reynolds number leads to a shorter extension of the laminar section in agreement with the data of previous studies. Estimations are made for typical values of the wavelength of oscillations corresponding to the revealed effect of sinusoidal instability and for the typical frequency of these oscillations, which sharply increases with the growth of Re.