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Journal ArticleDOI

Combustion in swirling flows: A review

01 Oct 1974-Combustion and Flame (Elsevier)-Vol. 23, Iss: 2, pp 143-201
TL;DR: The main effects of swirl are to improve flame stability as a result of the formation of toroidal recirculation zones and to reduce combustion lengths by producing high rates of entrainment of the ambient fluid and fast mixing as discussed by the authors.
About: This article is published in Combustion and Flame.The article was published on 1974-10-01. It has received 837 citations till now. The article focuses on the topics: Combustion chamber & Combustor.
Citations
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01 Jun 1978
TL;DR: In this paper, the authors evaluated the applicability of the standard κ-ϵ equations and other turbulence models with respect to their applicability in swirling, recirculating flows.
Abstract: The standard κ-ϵ equations and other turbulence models are evaluated with respect to their applicability in swirling, recirculating flows. The turbulence models are formulated on the basis of two separate viewpoints. The first perspective assumes that an isotropic eddy viscosity and the modified Boussinesq hypothesis adequately describe the stress distributions, and that the source of predictive error is a consequence of the modeled terms in the κ-ϵ equations. Both stabilizing and destabilizing Richardson number corrections are incorporated to investigate this line of reasoning. A second viewpoint proposes that the eddy viscosity approach is inherently inadequate and that a redistribution of the stress magnitudes is necessary. Investigation of higher-order closure is pursued on the level of an algebraic stress closure. Various turbulence model predictions are compared with experimental data from a variety of isothermal, confined studies. Supportive swirl comparisons are also performed for a laminar flow case, as well as reacting flow cases. Parallel predictions or contributions from other sources are also consulted where appropriate. Predictive accuracy was found to be a partial function of inlet boundary conditions and numerical diffusion. Despite prediction sensitivity to inlet conditions and numerics, the data comparisons delineate the relative advantages and disadvantages of the various modifications. Possible research avenues in the area of computational modeling of strongly swirling, recirculating flows are reviewed and discussed.

5,396 citations

Journal ArticleDOI
TL;DR: In this article, the authors reviewed the occurrence of the precessing vortex core (PVC) and other instabilities, which occur in, swirl combustion systems whilst identifying mechanisms, which allow coupling between the acoustics, combustion and swirling flow dynamics to occur.

894 citations

Journal ArticleDOI
TL;DR: The authors reviewed the studies undertaken on vortex breakdown over the past 45 years and provided a "guide" to the literature and where necessary directed the reader to more indepth reviews in specific areas.

722 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a survey of vortex breakdown, which is a disturbance characterized by the formation of an internal stagnation point on the vortex axis, followed by reversed flow in a region of limited axial extent.
Abstract: The term 'vortex breakdown', as used in the reported investigation, refers to a disturbance characterized by the formation of an internal stagnation point on the vortex axis, followed by reversed flow in a region of limited axial extent. Two forms of vortex breakdown, which predominate, are shown in photographs. One form is called 'near-axisymmetric' (sometimes 'axisymmetric'), and the other is called 'spiral'. A survey is presented of work published since the 1972 review by Hall. Most experimental data taken since Hall's review have been in tubes, and the survey deals primarily with such cases. It is found that the assumption of axial-symmetry has produced useful results. The classification of flows as supercritical or subcritical, a step that assumes symmetry, has proved universally useful. Experiments show that vortex breakdown is always preceded by an upstream supercritical flow and followed by a subcritical wake. However, a comparison between experiments and attempts at prediction is less than encouraging. For a satisfactory understanding of the structure of vortex breakdown it is apparently necessary to take into account also aspects of asymmetry.

687 citations

Journal ArticleDOI
TL;DR: In this article, the major features of the characterization of swirl flow combustion, with emphasis on application to practical combustors, are surveyed with special regard to the main effects of swirl on the performance, stability, and combustion intensity of flames in combustors.
Abstract: Consideration is given to the major features of the characterization of swirl flow combustion, with emphasis on application to practical combustors. Recent experimental work is surveyed first with special regard to the main effects of swirl on the performance, stability, and combustion intensity of flames in combustors. Since solution of the basic governing equations yields predictions that are realistic only if the physical processes are sufficiently well expressed in mathematical form and suitable computational methods of solution are employed, these details are discussed. The treatment is brief, since extensive reviews are available in the literature. It is possible to predict major features of these swirling flows and some solutions are exhibited. The achievements and current status of serial flow combustion are summarized.

410 citations

References
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Journal ArticleDOI
TL;DR: In this paper, it is shown that vortex breakdown is not a manifestation of instability or of any other effect indicated by study of infinitesimal disturbances alone, but instead a finite transition between two dynamically conjugate states of axisymmetric flow, analogous to the hydraulic jump in open-channel flow.
Abstract: The phenomenon examined is the abrupt structural change which can occur at some station along the axis of a swirling flow, notably the leading-edge vortex formed above a delta wing at incidence. Contrary to previous attempts at an explanation, the belief demonstrated herein is that vortex breakdown is not a manifestation of instability or of any other effect indicated by study of infinitesimal disturbances alone. It is instead a finite transition between two dynamically conjugate states of axisymmetric flow, analogous to the hydraulic jump in openchannel flow. A set of properties essential to such a transition, corresponding to a set shown to provide a complete explanation for the hydraulic jump, is demonstrated with wide generality for axisymmetric vortex flows; and the interpretation covers both the case of mild transitions, where an undular structure is developed without the need arising for significant energy dissipation, and the case of strong ones where a region of vigorous turbulence is generated. An important part of the theory depends on the calculus of variations; and the comprehensiveness with which certain properties of conjugate flow pairs are demonstrable by this analytical means suggests that present ideas may be useful in various other problems.

656 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe some experiments in swirling flows in a diverging cylindrical tube in which various types of vortex breakdowns were observed, viz. mild (double helix) breakdown, spiral breakdown, and axisymmetric breakdown.
Abstract: This paper describes some experiments in swirling flows in a diverging cylindrical tube in which various types of vortex breakdowns were observed.In one set of experiments, the position of the breakdown, axial component of the velocity of the vortex core, swirl angle distribution ahead of the breakdown, and the pressure distribution along the tube were determined for various flow rates and for various values of circulation imparted to the fluid (water). Basically, three types of vortex breakdown were observed, viz. mild (double helix) breakdown, spiral breakdown (followed by turbulent mixing), and axisymmetric breakdown (followed by a thicker vortex core, then a spiral breakdown, and finally by turbulent mixing). The type and the location of the stationary breakdowns were found to be dependent, for the particular vortex tube used, upon the Reynolds and circulation numbers of the flow. In a spiral breakdown, the vortex core filament maintained the same sense of rotation as the upstream fluid elements. In an axisymmetric breakdown, the bubble included an inclined vortex-ring whose axis gyrated about the axis of the tube.In a second set of experiments, the response of the abrupt structural change along the axis of flow to gradual and abrupt changes in the upstream and downstream flow conditions was examined. The axisymmetric breakdown responded in a manner analogous to the hydraulic jump in open-channel flow before if reached a new stationary position along the axis of the tube.The observations reported and the evidence presented herein revealed that the axisymmetric breakdown is a finite transition between two sequent states of flow as proposed by Benjamin (1962, 1965, 1967) on theoretical grounds.

554 citations

Journal ArticleDOI
TL;DR: In this article, a cylindrical vortex, formed in a long tube, was used to study the "vortex breakdown" that has been previously reported in investigations of the flow over slender delta wings.
Abstract: This paper describes an experiment in which a cylindrical vortex, formed in a long tube, was used to study the ‘vortex breakdown’ that has been previously reported in investigations of the flow over slender delta wings. By varying the amount of swirl that was imparted to the fluid before it entered the tube, it was found that the breakdown was the intermediate stage between the two basic types of rotating flows, that is, those that do and those that do not exhibit axial velocity reversal. In addition, it was shown that an unusual flow pattern was established after the breakdown and that certain features of this pointed to it being a ‘critical’ phenomenon. The tests were concluded by measuring the swirl angle distribution a short distance ahead of the breakdown and comparing these results with the prediction of Squire's theory (1960).

254 citations