Full-field measurements of self-excited oscillations in momentum-dominated helium jets

• Published in: Experiments in fluids Vol. 38; no. 2; pp. 161 - 173
• Main Authors: YILDIRIM, B. S, AGRAWAL, A. K
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.02.2005; Berlin
• Subjects: Buoyancy; Buoyancy-driven instability; Exact sciences and technology; Fluid dynamics; Fluid flow; Fundamental areas of phenomenology (including applications); Helium; Hydrodynamic stability; Instrumentation for fluid dynamics; Jets; Oscillations; Physics; Transition to turbulence; Turbulence; Turbulent flow; Turbulent flows, convection, and heat transfer; Concentration measurement; Flow visualization; Jets; Schlieren method; Selfoscillation; Experimental study; Helium; Turbulent laminar transition
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-004-0878-z

Flow structure of momentum-dominated helium jets discharged vertically into ambient air was investigated using a high-speed rainbow schlieren deflectometry (RSD) apparatus operated at up to 2,000 Hz. The operating parameters, i.e., Reynolds number and Richardson number were varied independently to examine the self-excited, flow oscillatory behavior over a range of experimental conditions. Measurements revealed highly periodic oscillations in the laminar region at a unique frequency as well as high regularity in the flow transition and initial turbulent regions. The buoyancy was shown to affect the oscillation frequency and the distance from the jet exit to the flow transition plane. Instantaneous helium concentration contours across the field of view revealed changes in the jet flow structure and the evolution of the vortical structures during an oscillation cycle. A cross-correlation technique was applied to track the vortices and to find their convection velocity. Time traces of helium concentration at different axial locations provided detailed information about the oscillating flow.