Abstract
An axisymmetric air jet flow is experimentally investigated under passive flow control. The jet issues from a pipe of the inner diameter and length of 10 mm and 150 mm which is equipped with an axisymmetric cavity at the pipe end. The cavity operates as a resonator creating self-sustained acoustic excitations of the jet flow. A mechanism of excitations is rather complex – in comparison with a common Helmholtz resonator. The experiments were performed using flow visualization, microphone measurements and time-mean velocity measurements by the Pitot probe. The power spectral density (PSD) and the sound pressure level (SPL) were evaluated from microphone measurements. The jet Reynolds number ranged Re = 1600–18 000. Distinguishable peaks in PSD indicated a function of the resonator. Because the most effective acoustic response was found at higher Re , a majority of experiments focused on higher Re regime. The results demonstrate effects of the passive control on the jet behavior. Fluid mixing and velocity decay along the axis is intensified. It causes shortening of the jet transition region. On the other hand, an inverse proportionality of the velocity decay ( u ~ 1/ x ) in the fully developed region is not changed. The momentum and kinetic energy fluxes decrease more intensively in the controlled jets in comparison with common jets.
Highlights
A jet flow is a type of fluid motion and one of basic types of shear flows
The results demonstrate effects of the passive control on the jet behavior
The jet flow is very important from practical engineering point of view because it is frequently used in industrial applications such as fluid mixing, control of flow and thermal fields, thrust generation, convective heat transfer, and combustion and chemical processes
Summary
A jet flow is a type of fluid motion and one of basic types of shear flows. The jet flow is very important for theoretical studies in fluid mechanics – see Schlichting [1], Abramovich [2]. The jet flow is very important from practical engineering point of view because it is frequently used in industrial applications such as fluid mixing, control of flow and thermal fields, thrust generation, convective heat transfer, and combustion and chemical processes. It is worth noting here that unsteadiness is not a foreign feature to the continuous (steady) jets, quite the contrary, a tendency to form natural organized structures and oscillations are intrinsically incorporated in all jet flows – see, e.g., Crow and Champagne [3]
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