CFD analysis of free shear layer approximations for a pulsed air jet

摘要

We propose a numerical investigation on the validity of the free shear layer approximations for laminar 2D pulsed jets in both isothermal and heated configurations. More precisely, we determine the range of values for the Strouhal number St and amplitude of the perturbation A for which these approximations remains valid. For this, we have considered a two-dimensional air jet exhausting into a quiescent environment. At the nozzle exit, the flow is characterized by a uniform temperature T_0 and submitted to a longitudinal and periodic velocity disturbance: u = u_0 + α * sin(ωt). A finite volume method is performed to solve the general Navier-Stokes equations governing this flow type. The present study is evaluated by comparing with previous numerical results. Conclusions are drawn about the ability of a model that does not consider the shear layer approximations to handle properly the behavior of pulsed air jet. The discussion relates to the effect of the most significant parameters, such as the pulsation frequency and amplitude, on the flow characteristic fields. The effect of Reynolds and Grashof numbers was also examined. The results state that the free shear layer approximations are valid in different regions of the isothermal or the heated pulsed jet, and this, only for high Strouhal numbers (St ≥ 1) and for low pulsation amplitude (A ＜ 3%) Otherwise, these approximations remain valid for a free pulsed jet only in the fully developed flow region.