Phase averaged velocity field in an axisymmetric jet subject to a sudden velocity decrease

• Published in: Experiments in fluids Vol. 21; no. 6; pp. 447 - 456
• Main Authors: Borée, J., Atassi, N., Charnay, G.
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.10.1996; Berlin
• Subjects: Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Jets; Physics; Turbulent flows, convection, and heat transfer; Fluctuations; Flow distortion; Turbulent flow; Circular jet; Disturbances; Velocity distribution; Experimental study; Hot wire anemometers
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/BF00189047

An unsteady transient axisymmetric turbulent jet was studied experimentally. The initial flow perturbation consisted of a sudden and large decrease in the ejection velocity. The temporal evolution of the mean and fluctuating unsteady velocity field was measured by using X hot-wire probes. In the jet far field, adaptation of the externally imposed unsteadiness to the local jet time scale is confirmed quantitatively. The main features of the phase averaged velocity field are presented and comments are made about the instantaneous state of the turbulence energetics. Transient mean radial velocities are deduced and an important increase of the instantaneous rate of entraining external fluid into the jet is found. Finally, we show that the pressure effect due to radial impulse terms plays an important role in the propagation of the mean perturbation. The longitudinal adaptation of the perturbation time scale driven by the local jet time scale provides a turbulent flow that is intermediate to quasi-static flows and rapidly distorted flows. (Author)