The transition to turbulence of buoyant near-critical water jets

• Published in: The Journal of supercritical fluids 2014-11, Vol.95, p.195-203
• Main Authors: Hegde, U., Gotti, D., Hicks, M.
• Format: Article
• Language: English
• Subjects: Buoyancy; Fluid dynamics; Fluid flow; Fluids; Froude number; Jets; Reynolds number; Supercritical; Transition; Turbulence; Turbulent flow
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2014.08.005

•Observations on transition to turbulence of near-critical water jets are reported.•Two types of transition are primarily observed as Reynolds number (Re) is increased.•The first type is classical with a transition point that moves upstream with increasing Re.•In the second type the entire jet is turbulent even at low Re.•The low Re behavior is determined by the Prandtl number and Froude number. Observations of near-critical water jets are reported in the injection Reynolds number range of approximately 300–3000 to characterize their transition to turbulence. Three types of cases are described: (i) subcritical jet injected into subcritical water, (ii) supercritical jet injected into supercritical water, and (iii) supercritical jet injected into subcritical water. In each case, the working pressure was kept above the critical value to eliminate two-phase effects. For cases (i) and (ii), the transition behavior follows well known characteristics with transition to turbulence initially occurring near the tip of the jet with the transition location moving upstream nearer to the nozzle exit with an increase in injection Reynolds number. However, the transition behavior for case (iii) is quite different with significant buoyant effects leading to turbulent behavior at lower Reynolds numbers. Consideration of the pseudocritical region with strongly varying fluid properties, which is established in the mixing region between the jet and the cell fluid, yields an effective Froude number that is useful to elucidate this difference. The effective Froude number incorporates the Prandtl number of the mixing region to account for the large disparity between viscous and thermal length scales.