An experimental investigation of swirling jets

Abstract

The ‘plug’ flow emerging from a long rotating tube into a large stationary reservoir has been used in an experimental investigation of centrifugally unstable swirling jets. A moderate Reynolds number, $\hbox{\it Re}\,{=}\,1000$, was studied extensively, and swirl numbers, $S$, the ratio of nozzle exit rotating speed to the mean mass axial velocity, were in the range 0–1.1. Four regimes were covered: non-swirling jets with $S\,{=}\,0$, weakly swirling jets in the range $0\,{<}\,S\,{<}\,S_{c1}$, strongly swirling jets before vortex breakdown with $S_{c1}\,{<}\,S\,{<}\,S_{c2}$, and stable vortex breakdown for $S\,{>}\,S_{c2}$, where $S_{c1}\,{=}\,0.6$ and $S_{c2}\,{=}\,0.88$.

Bistable swirled flames and influence on flame transfer functions

“…The PVC is an hydrodynamic instability in swirling flows [3].I t is a large scale structure characterized by a regular rotation of a spiral structure around the geometrical axis of the combustion chamber. It can occur at high Reynolds and swirl number flows [4][5][6][7][8][9][10] and its precession frequency is controlled by the rotation rate of the swirled flow [3].…”

“…It can occur at high Reynolds and swirl number flows [4][5][6][7][8][9][10] and its precession frequency is controlled by the rotation rate of the swirled flow [3]. Several studies show that combustion can suppress the PVC [6,7,11], but other cases also show PVCs which are present in reacting flows [12][13][14][15].…”

“…They feature several types of vortex breakdown and can exhibit bifurcation phenomena where different states can co-exist and the flow can jump spontaneously from one to another [1,2]. Bifurcations of flames in configurations which are close to real gas turbine chambers have not been investigated so far even though engineers report that they observe these mechanisms and that there is a link between flame states and thermoacoustic instabilities: when the flame changes from one state to another, its acoustic stability characteristics also change.Two dynamic phenomena are usually observed in swirled combustion chambers: (1) a helical flow instability, the so-called precessing vortex core (PVC) and (2) thermo-acoustic instabilites.The PVC is an hydrodynamic instability in swirling flows [3].I t is a large scale structure characterized by a regular rotation of a spiral structure around the geometrical axis of the combustion chamber. It can occur at high Reynolds and swirl number flows [4][5][6][7][8][9][10] and its precession frequency is controlled by the rotation rate of the swirled flow [3].…”

Impact of rotating and fixed nozzles on vortex breakdown in compressible swirling jet flows

“…The studies mainly split up in two groups, either utilizing a long rotating pipe with a straight or contracting nozzle attached, e.g. Liang and Maxworthy [8] and Facciolo et al [9], or a pipe and a nozzle at rest in combination with a rotating honeycomb or guiding vanes to generate swirl, e.g. Billant et al [5], Gallaire et al [10], Oberleithner et al [4] and Leclaire and Jacquin [11].…”

“…Liang and Maxworthy [8] and Liang and Maxworthy [12] used a long rotating pipe attached to a large water tank to generate swirling jets. The authors conducted experiments at Reynolds numbers up to Re D = 2000 (based on the bulk velocity).…”