Flow Visualization of Vortex Structure of an Excited Coaxial Jet

Article type: Research Article

Authors: Kiwata, T. | Okajima, A. | Kimura, S.

Affiliations: Department of Mechanical Systems Engineering, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa 920-8667, Japan.

Abstract: This paper describes the results of experimental and numerical studies concerning the near-field vortical structure and dynamics of a coaxial jet. The effect of excitation of annular and circular jets on the vortical structure in the inner and outer shear-layers was studied. The flow visualization and the measurements of mean and fluctuating velocities, by a hot-film probe and the particle image velocimetry (PIV) technique, were carried out in an open water tank. The results of flow visualization and numerical simulation are in good agreement. With the excitation of a half of the initial vortex frequency, it is found that the vortex-pairing event is promoted by the forced excitation and it results in the rapid expansion of the jet width and the increase of velocity fluctuation and the entrainment rate. For the velocity ratio near unity, the dominant peak frequency coincides with the initial vortex frequency, i.e., the lip wake vortex frequency, independent of the forced excitation frequency.

Keywords: coaxial jet, excited jet, flow control, vortex pairing, particle image velocimetry

Journal: Journal of Visualization, vol. 4, no. 1, pp. 99-107, 2001