TY - GEN
T1 - The determination of formation number for starting buoyant jets
AU - Wang, Ruo Qian
AU - Law, Adrian Wing Keung
AU - Eric Adams, E.
AU - Fringer, Oliver B.
PY - 2010
Y1 - 2010
N2 - Starting buoyant jets are widely observed in nature as well as in engineering applications. The interactions between the leading vortex ring and the trailing stem play a significant role on the development of the staring processes, and the Formation Number is established to be the criterion that demarcates the presence of the trailing stem and thus, the occurrence of pinch-off. In this study, the buoyant formation number for a starting buoyant jet which includes the momentum inducement due to presence of buoyancy is examined numerically. The investigation is based on the results of a series of numerical simulations with the Large-Eddy Simulation (LES) approach to reproduce the starting buoyant jet in a wide range of conditions from pure jets to lazy plumes. Based on the results, the buoyant formation number can be obtained following the occurrence of a step-jump in the vortex ring circulation in the following manner. First, the vorticity is integrated through the half central plane of the computational domain, which a trough can be observed to follow the head vortex ring in the vertical distribution. The trailing stem and the head vortex ring are differentiated based on this trough location. Subsequently, if and just before a pitch off occurs, a step-jump in the circulation of the head vortex ring is typically observed. The jump value is then traced back to the total circulation, and the non-dimensional time that it occurs. This non-dimensional time is found to the same as the formation number for the runs conducted. Using this method, a comparison of the numerical results with the experimental data for a starting pure jet is performed, and the widely accepted formation number (≈4.0) is obtained which verifies that the method is satisfactory. The effect of buoyancy on the formation number is then investigated for two turbulent discharge conditions of Re=2000 and 2500 and with a wide range of buoyancy fluxes.
AB - Starting buoyant jets are widely observed in nature as well as in engineering applications. The interactions between the leading vortex ring and the trailing stem play a significant role on the development of the staring processes, and the Formation Number is established to be the criterion that demarcates the presence of the trailing stem and thus, the occurrence of pinch-off. In this study, the buoyant formation number for a starting buoyant jet which includes the momentum inducement due to presence of buoyancy is examined numerically. The investigation is based on the results of a series of numerical simulations with the Large-Eddy Simulation (LES) approach to reproduce the starting buoyant jet in a wide range of conditions from pure jets to lazy plumes. Based on the results, the buoyant formation number can be obtained following the occurrence of a step-jump in the vortex ring circulation in the following manner. First, the vorticity is integrated through the half central plane of the computational domain, which a trough can be observed to follow the head vortex ring in the vertical distribution. The trailing stem and the head vortex ring are differentiated based on this trough location. Subsequently, if and just before a pitch off occurs, a step-jump in the circulation of the head vortex ring is typically observed. The jump value is then traced back to the total circulation, and the non-dimensional time that it occurs. This non-dimensional time is found to the same as the formation number for the runs conducted. Using this method, a comparison of the numerical results with the experimental data for a starting pure jet is performed, and the widely accepted formation number (≈4.0) is obtained which verifies that the method is satisfactory. The effect of buoyancy on the formation number is then investigated for two turbulent discharge conditions of Re=2000 and 2500 and with a wide range of buoyancy fluxes.
KW - Large-Eddy simulation
KW - buoyant formation number
KW - plume
KW - trailing stem
KW - vortex ring
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U2 - 10.1063/1.3452156
DO - 10.1063/1.3452156
M3 - Conference contribution
AN - SCOPUS:77955733838
SN - 9780735407787
T3 - AIP Conference Proceedings
SP - 1636
EP - 1641
BT - ISCM II and EPMESC XII - Proc. of the 2nd Int. Symposium on Computational Mechanics and the 12th Int. Conf. on the Enhancement and Promotion of Computational Methods in Engineering and Science
T2 - 2nd International Symposium on Computational Mechanics, ISCM II, and the 12th International Conference on the Enhancement and Promotion of Computational Methods in Engineering and Science, EPMESC XII
Y2 - 30 November 2009 through 3 December 2009
ER -