Experimental Study of Unconfined and Confined Isothermal Swirling Jets
A 3C-2D PIV technique was applied to investigate the swirling flow generated by an axial plus tangential type swirl generator. This work is focused on the near-exit region of an isothermal swirling jet to characterize the effect of swirl on the flow field and to identify the large coherent structures both in unconfined and confined conditions for geometrical swirl number, Sg = 4.6. Effects of the Reynolds number on the flow structure were also studied. The experimental results show significant effects of the confinement on the mean velocity fields and its fluctuations. The size of the recirculation zone was significantly enlarged upon confinement compared to the free swirling jet. Increasing in the Reynolds number further enhanced the recirculation zone. The frequency characteristics have been measured with a capacitive microphone which indicates the presence of periodic oscillation related to the existence of precessing vortex core, PVC. Proper orthogonal decomposition of the jet velocity field was carried out, enabling the identification of coherent structures. The time coefficients of the first two most energetic POD modes were used to reconstruct the phase-averaged velocity field of the oscillatory motion in the swirling flow. The instantaneous minima of negative swirl strength values calculated from the instantaneous velocity field revealed the presence of two helical structures located in the inner and outer shear layers and this structure fade out at an axial location of approximately z/D = 1.5 for unconfined case and z/D = 1.2 for confined case. By phase averaging the instantaneous swirling strength maps, the 3D helical vortex structure was reconstructed.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1128929Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 788
 K. Gupta, D.G. Lilley, N. Syred, Swirl Flows. Abacus Press, 1984.
 N. Syred, “A review of oscillation mechanisms and the role of the precessing vortex core (PVC) in swirl combustion systems,” Progress in Energy and Combustion. Science, vol. 32(2), pp. 93–161, 2006.
 P. Billant, J.M. Chomaz, P. Huerre, “Experimental Study of Vortex Breakdown in Swirling Jets,” Journal of Fluid Mechanics, Vol. 376, pp. 183–219, 1998.
 R. Chanaud, “Observations of oscillatory motion in certain swirling flows,” J Fluid Mech 21:111–127, 1965.
 O. Lucca-Negro, T. O’Doherty, “Vortex breakdown,” A review. Prog. Energy Combust. Sci. 27, 431, 2001.
 C.E. Cala, E.C.Fernandes, M.V. Heitor, S.I. Shtork, “Coherent structures in unsteady swirling jet flow,” Exp Fluids 40:267–276, 2006.
 F. Martinelli, F. Cozzi, A. Coghe, “Phase-locked analysis of velocity fluctuations in a turbulent free swirling jet after vortex breakdown,” Exp Fluids. 53:437-449, 2012.
 N. Syred, J.M. Beer, “Combustion in swirling flows: a review,” Combustion and Flame, 23:143–201, 1974.
 A.E.E. Khalil, J.M Brooks, A.K. Gupta, “Impact of confinement on flowfield of swirl flow burners,” Fuel 184, 1–9. 5, 2016.
 G. Ceglia, S. Discetti, A Ianiro, “Three-dimensional organization of the flow structure in a non-reactive model aero engine lean burn injection system,” Exp ThermFluid Sci 52:164–173, 2014.
 M. Negri, F. Cozzi, S. Malavasi, “Self-synchronized phase averaging of PIV measurements in the base region of a rectangular cylinder,” Meccanica 46: 423-435, 2010.
 B.W. van Oudheusden, F. Scarano, N.P. van Hinsberg, D.W. Watt, “Phase-resolved characterization of vortex shedding in the near wake of a square-section cylinder at incidence,” Exp Fluids 39: 86-98, 2005.
 K. Oberleithner, M. Sieber, C.N. Nayeri, C.O. Paschereit, C Petz, H.C. Hege, “Three-dimensional coherent structures in a swirling jet undergoing vortex breakdown: stability analysis and empirical mode construction,” J Fluid Mech 679:383-414, 2011.
 M. Stohr, R. Sadanandan, W. Meier, “Phase-resolved characterization of vortex-flame interaction in a turbulent swirl flame.” Exp Fluids 51:1153-1167, 2011.
 H. Chen, D.L. Reuss, V. Sick, “On the use and interpretation of proper orthogonal decomposition of in-cylinder engine flows,” Meas Sci Technol 23: 085302, 2012.
 J.L. Lumley, “The structure of inhomogeneous turbulence,” In: Yaglom AM, Tatarski VI (eds) Atmospheric turbulence and wave propagation. Nauka, Moscow, 166-178, 1967.
 F. Cozzi, R. Sharma, A. Coghe, F. Arzuffi, “An experimental investigation on Isothermal free swirling jet,” XXXVIII Meeting of the Italian Section of the Combustion Institute, 2015, Lecce, Italy.
 S.M. Soloff, R.J Adrian, Z.C Liu, “Distortion compensation for generalized stereoscopic particle image velocimetry,” Meas. Sci. Technol.8:1441-1454, 1997.
 N.A. Chigier, A. Chervinsky A, “Experimental investigation of swirling vortex motion in jets,” J Appl Mech 34:443–451, 1967.
 N. Rajaratnam, Turbulent Jets. Elsevier, Amsterdam, 1976.
 T.C. Claypole, N. Syred, “The Effect of Swirl Burner Aerodynamics on NOx Formation,” International Symposium on Combustion, 1981, 18, 81–89.
 G. Berkooz, P. Holmes, J.L. Lumley, “The proper orthogonal decomposition in the analysis of turbulent flows,” Annu Rev Fluid Mech 25:539-575, 1993.
 L. Sirovich, “Turbulence and the dynamics of coherent structures,” Quart Appl Math 45: 561-590, 1987.
 H. Liang, T. Maxworthy, “An experiment investigation of swirling jets,” J Fluid Mech 525:115–159, 2005.
 S. Archer, A.K. Gupta, “The role of confinement on flow dynamics under fuel lean combustion,” In: 2nd international energy conversion engineering conference, 16–19 August, Providence, RI. Paper#AIAA-5617, 2004.
 P. Chong, W. Hongping, W. Jinjun, “Phase identification of quasi-periodic flow measured by particle image velocimetry with a low sampling rate,” Measurement Science and Technology 24:055305, 2013.
 R. Sharma, F. Cozzi, A. Coghe, “Phase-averaged characterization of turbulent isothermal free swirling jet after vortex breakdown,” Proc.18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics, 2016, Lisbon, Portugal.
 D.M Markovich, S.S Abdurakipov, L.M Chikishev, “Comparative analysis of low- and high swirl confined flames and jets by proper orthogonal and dynamic mode decompositions,” Phys Fluids 26:065109, 2014.
 G. John, P. Dimitris, G. Manolakis, Digital signal processing (3rd ed.): principles, algorithms, and applications, Prentice-Hall, NJ, USA, 1996.
 K. E. Meyer, D. Cavar, J. M. Pedersen, "POD as tool for comparison of PIV and LES data,” 7th International Symposium on Particle Image Velocimetry, 2007, Rome, Italy