Coherent Structures and Turbulent Transport in the Initial Region of Jets and Flame in Swirling Flow
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COHERENT STRUCTURES AND TURBULENT TRANSPORT IN THE INITIAL REGION OF JETS AND FLAME IN SWIRLING FLOW A. S. Lobasov∗ , L. M. Chikishev,
UDC 532.525.2, 532.529.3, 544.452.42
V. M. Dulin, and D. M. Markovich
Abstract: This paper presents the results of experimental studies of the spatial flow structure and coherent structures in the initial region of swirling jets at a Reynolds number of 5000 and different swirl rates. The contribution of these structures to the turbulent transport of momentum and mass was first quantitatively evaluated. In addition, for the case of high swirl with vortex core breakdown, the effect of coherent structures on the fluctuation in the local heat release rate due to the deformation of the flame front was investigated for combustion of a methane–air mixtures with an air excess ratio of 1.43. Keywords: swirling jet in the presence of combustion, vortex core breakdown, coherent structures, turbulent transport of heat and mass. DOI: 10.1134/S0021894420030050 INTRODUCTION Regulatory requirements for power plant emission become more and more stringent, necessitating the development of low-emission combustion chambers operating at high efficiency. Currently developed gas turbine combustors are based on the technology of a partially mixed mixture with a significant excess of air [1, 2]. For ignition and stable combustion in gas turbine combustors, it is common to use flow swirling [3, 4], which provides combustion in a compact area in wide ranges of flow rates and equivalence ratios. The following features of inlet swirling flow into a combustion chamber contribute to flame stabilization: the presence of a reduced pressure region in the center of the vortex core, where hot combustion products accumulate; flow deceleration during the passage of the vortex core and the formation of a wake (or a recirculation zone with a high swirl rate) [5, 6]; centrifugal instability of the vortex core, its precession, and breakdown (which also occurs for large values of the swirl rate) [7–10]. As a rule, vortex core breakdown is due to flow transition to strong turbulence, the formation of a central recirculation zone, and intense fluctuations of pressure (and velocity) at a particular frequency. In some papers, a significant decrease in the amplitude of fluctuations after ignition has been reported, and in other studies, a significant reduction in the fluctuation level has not been found [11, 12]. Combustion in swirling jets in the presence of a precessing vortex core and the effect of this process on flame stabilization have been the subject of numerous studies [13, 14]. Recently, considerable research effort has focused on the experimental study of the effect of combustion on the structure of swirling flows using particle image velocimetry (PIV) and its stereoscopic modification [15–17].
Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia; ∗ [email protected]; [email protected]; [email protected]; [email protected]. Translated from Prikladnaya Mekhanika i Tekhnicheskay
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