Experimental investigation of synthetic jet impingement upon a honeycomb

Abstract

We present an experimental study of synthetic jet vortex rings flowing through a honeycomb. A free synthetic jet generated by piston-cylinder apparatus is used to make a vortex, obtaining turbulence at Taylor Reynolds number Re_λ ∼ 294. We sketch a conceptual picture of the passive control of the flow field by honeycomb. By choosing a length-to-cell ratio Φ = 2.1, we clearly show how the honeycomb affects the evolution of vortical structure flowing through a honeycomb. The mechanism associated with vorticity cancellation is that the finger-type jets shaping downstream of the honeycomb will reorganize into a transmitted vortex ring in the downstream flow. We chose three length-to-cell ratios (Φ = 3.7, 6.3, and 12.5) with a constant length of honeycomb to examine the effect of their geometry on the flow characteristic. We find that honeycomb redistributes the flow field and enhances the uniformity of the flow field. In addition, the selection of the length-to-cell ratio of honeycomb should correspond to the given experimental conditions, because the turbulence reduction and isotropy are not mutually beneficial. The results of velocity triple-decomposition show that the honeycomb can effectively reduce the periodic and random velocity fluctuation, revealing the mechanism of a relaminarization.