Experimental investigation of vortex breakdown in a coaxial swirling jet with a density difference

Abstract

c We studied a stable vortex breakdown in a variable-property coaxial swirling jet. c A model using common nondimensional numbers is proposed to explain the following. c The height of the stagnation point increases with increasing outer jet velocity. c The height of the stagnation point is always lower for a denser inner jet. c The model is fairly successful in explaining the trends observed in our study. a r t i c l e i n f o t r a c tIn this work we experimentally investigate the behavior of stable vortex breakdown taking place in a coaxial swirling jet with a density difference, highlighting the effect of the outer jet on the height of the stagnation point. With increasing bulk flow velocity of the outer jet, the degree of flow divergence decreases, resulting in an increase in the height of the stagnation point. This is due to a significant increase in the mean axial velocity along the centerline of the jet, which is clearly shown by particle image velocimetry (PIV). We proposed an equation to physically explain the height of the stagnation point in a coaxial swirling jet with a density difference undergoing vortex breakdown, by considering an estimate of the momentum balance in the flow, based on a simplified Navier-Stokes equation for coaxial jets with coannular flow. Even though the effect of the density difference on the height of the stagnation point is overestimated by the proposed equation, the increase with respect to the Reynolds number of the outer jet observed experimentally is in reasonably good qualitative agreement with the trend predicted by the theoretical model.

Hysteresis and turbulent vortex breakdown in transitional swirling jets

“…(2015), figures 4 and 5 in Tammisola & Juniper (2016), figure C.8 in Falese et al. (2014), figures 3 and 4 in Jiang & Shen (1994), figure 5 in Adzlan & Gotoda (2012) and figure 5 in Apte et al. (2003) show flow states with features resembling CVB, although further investigation is required to confirm if these flow states are the CVB.…”

“…Indeed, the cases shown in figure 17 strongly resemble that shown in figure 5(b) of Liang & Maxworthy (2005) even though the Reynolds numbers in that study is only half of the value used here. Similarly, figure 45 in Syred & Beer (1974), figure 7 in Gore & Ranz (1964), figure 3 in Aguilar et al (2015), figures 4 and 5 in Tammisola & Juniper (2016), figure C.8 in Falese et al (2014), figures 3 and 4 in Jiang & Shen (1994), figure 5 in Adzlan & Gotoda (2012) and figure 5 in Apte et al (2003) show flow states with features resembling CVB, although further investigation is required to confirm if these flow states are the CVB.…”

Vortex breakdown in variable-density gaseous swirling jets

“…There is interest, therefore, in characterizing effects of varying density on vortex breakdown of laminar jets, extending the previous constant-density analyses to gas-jet configurations with jet-to-ambient density ratios that differ from unity. Such effects were investigated experimentally by Adzlan & Gotoda (2012) for a coaxial configuration involving either an air jet or a carbon dioxide jet, both discharging into an air coflow. The experiments revealed that the heavier carbon dioxide jet exhibits a greater degree of flow divergence and lower critical swirl numbers than the air jet, and that augmenting the coflow velocity decreases the flow divergence and tends to suppress vortex breakdown.…”

“…The present work employs theoretical and numerical techniques to study vortex breakdown in variable-density laminar swirling jets. Unlike the experimental analysis by Adzlan & Gotoda (2012), our work addresses a wide range of jet-to-ambient density differences and provides a systematic approach to identifying the onset of both forms of breakdown, which has not previously been done. To test the methods and investigate possible quantitative differences from the results published previously for constant-density swirling jets, the flow conditions considered include, in particular, those of the previous numerical investigations (Ruith, Chen & Meiburg 2004;Moise & Mathew 2019;Moise 2020).…”

Direct Numerical Simulation of Twin Swirling Flow Jets: Effect of Vortex-Vortex Interaction on Turbulence Modification

“…Iyogun et al [7] used PIV approach to investigate the stability of swirling nonpremixed flame with different nozzle geometries. Adzlan and Gotoda [8] studied the behavior of stable vortex breakdown occurring in a coaxial swirling jet with a density difference experimentally and considered the effect of density difference on the height of stagnation point. Litvinov et al [9] performed an experimental study of strongly swirling air flow with high Reynolds number to characterize precessing vortex core (PVC) and proved an analytical model of a helical vortex which is useful to describe or predict PVC.…”