Control of a Round Jet Intermittency and Transition to Turbulence by Means of an Annular Synthetic Jet

Zuzana Antošová,Zdeněk Trávníček

doi:10.3390/act10080185

Abstract

This paper deals with active control of a continuous jet issuing from a long pipe nozzle by means of a concentrically placed annular synthetic jet. The experiments in air cover regimes of laminar, transitional, and turbulent main jet flows (Reynolds number ranges 1082–5181). The velocity profiles (time-mean and fluctuation components) of unforced and forced jets were measured using hot-wire anemometry. Six flow regimes are distinguished, and their parameter map is proposed. The possibility of turbulence reduction by forcing in transitional jets is demonstrated, and the maximal effect is revealed at Re = 2555, where the ratio of the turbulence intensities of the forced and unforced jets is decreased up to 0.45.

Highlights

Fluid jet flows are one of the free shear flows that occur without a direct impact of wall boundaries on fluid motion
The objective of the present study is to experimentally demonstrate and quantify flow control possibilities in the case of a coaxial arrangement of the main and control jets
The first resonance of the actuator results from a transformation between the potential energy of the diaphragm and the jet kinetic energy during each period

Summary

Introduction

Fluid jet flows are one of the free shear flows that occur without a direct impact of wall boundaries on fluid motion. The fluid motion can be laminar or turbulent in character. The governing parameter is the Reynolds number, Re = Um D/ν, where Um is the mean velocity through the nozzle producing the jet, D is the characteristic scale, which is the nozzle diameter for round jets, and ν is the kinematic viscosity of the working fluid. The laminarturbulent transition (or onset of turbulence) is linked with the critical Reynolds number,. (typically Rec ~2300), the transition in jets occurs at Re and is about two orders of magnitude smaller due to an absence of the wall stabilization effects.

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Conclusion