Characterization of a synthetic jet vortex ring flowing through honeycomb

Abstract

The investigation of synthetic jet vortex rings flowing through a honeycomb is measured by two-dimensional particle-image velocimetry. The vortex is established using free synthetic jets generated by a piston–cylinder apparatus upstream of the honeycomb. On that basis, turbulence is obtained at circulation Reynolds numbers of ReΓ = 3437, 5155, 6874, and 8592, and Reynolds numbers of the synthetic jets of Resj = 561, 841, 1121, and 1402. The effects of the diameter Reynolds number (ReM = 41–449) and the length-to-cell ratio of the honeycomb (Φ = 4.2–12.5) on the characterization of flow are discussed in detail. A combinatorial similarity parameter that can characterize the effect of passive control on flow fields using a honeycomb is proposed and validated. The combinatorial similarity parameter, ReM/Φ, is determined through dimensional analysis and according to the change in momentum flux loss; its predictive capability is verified quantitatively based on the change in loss of kinetic energy and vortex-ring circulation. The evolutions of phase-averaged vorticity fields and finite-time Lyapunov exponents fields are nearly consistent using the close combinatorial similarity parameters. Furthermore, as indicated by the results, ReM/Φ responds to the combined effect of the relative magnitude of flow inertial and viscous forces, and the shape resistance of the honeycomb geometry to the flow-field–honeycomb interactions. Understanding the characterization of a vortex ring flowing through honeycomb is important for the accuracy of the prediction of turbulence models and the selection of the honeycomb size.