Single- and double-helix vortex breakdown as two dominant global modes in turbulent swirling jet flow

2020-01-25
Vanierschot, Maarten
Mueller, Jens S.
Sieber, Moritz
Perçin, Mustafa
van Oudheusden, Bas W.
Oberleithner, Kilian
In this paper, we study the shape and dynamics of helical coherent structures found in the flow field of an annular swirling jet undergoing vortex breakdown. The flow field is studied by means of time-resolved tomographic particle image velocimetry measurements. The obtained flow fields are analysed using both classic and spectral proper orthogonal decomposition. Despite the simple geometrical set-up of the annular jet, the flow field is very complex. Two distinct large-scale helical flow structures are identified: a single and a double helix, both co-rotating with the swirl direction, and it is revealed that these structures are not higher harmonics of each other. The structures have a relatively low energy content which makes it hard to separate them from other dynamics of the flow field, notably turbulent motions. Because of this, classic proper orthogonal decomposition fails to identify both structures properly. Spectral proper orthogonal decomposition, on the other hand, allows them to be identified accurately when the filter size is set at around eight times the precession period. The precession frequencies of the single and double helices correspond to Strouhal numbers of 0.273 and 0.536 +/- 0.005, respectively. A global stability analysis of the mean flow field shows that these structures correspond to two separate global modes. The precessing frequencies obtained by the stability analysis and the related spatial structures match very well with the experimental observations. The current work extends our knowledge on turbulent vortex breakdown and on mean field global stability theory in general. It leads to the following conclusions. Firstly, single- and double-helix vortex breakdown are both manifestations of global modes. Previous studies have shown that both m = 1 and m = 2 modes can coexist in swirling jets. However, the m = 2 mode has been identified as a second harmonic of the first mode, while this study identifies both as two independent global modes. Secondly, this work shows that the simultaneous occurrence of multiple helical global modes is possible within a turbulent flow and their shapes and frequencies are very well predicted by mean field stability analysis. The latter finding is of general interest as it applies to a wide class of fluid problems dominated by multiple oscillatory structures.
JOURNAL OF FLUID MECHANICS

Suggestions

Flow structure inside and around a rectangular array of rigid emerged cylinders located at the sidewall of an open channel
Köken, Mete (Cambridge University Press (CUP), 2021-01-01)
Flow structure inside and around a rectangular array of emerged cylinders located adjacent to the sidewall of an open channel is investigated using eddy-resolving numerical simulations. This configuration is particularly relevant for understanding how patches of aquatic vegetation developing near a river's banks affect flow and transport. The array of width W = 1.6D and length L = 33D-35D (D is the flow depth) contains rigid cylinders. Simulations with incoming, fully developed turbulent flow (channel Reyno...
Multi-scale characterization of particle clustering in discontinuously reinforced composites
CETIN, Arda; Kalkanlı, Ali (Elsevier BV, 2009-06-01)
The applicability of a quantitative characterization scheme for cluster detection in particle reinforced composites is discussed. The method considers the pattern from the perspective of individual particles, so that even in a pattern that globally conforms to a random distribution, micro-scale heterogeneities can be detected. The detected clusters are visualized by kernel surfaces. Results indicate that the presented methodology is an effective discriminator of clusters and can successfully be used for qua...
Receptances of non proportionally and continuously damped plates Reduced dampers method
Özgüven, Hasan Nevzat (Elsevier BV, 1982-12-01)
This paper presents a method for the dynamic analysis of continuously and non-proportionally damped plates in bending modes. The damping can be in the form of constrained or unconstrained layers. The method is an extension of the equivalent dampers method discussed in a previous paper, in which the damping matrix of a discretized plate is replaced by a diagonal equivalent damping matrix. Each diagonal element represents an equivalent damper inserted between the structure and ground. In this method the numbe...
Transient and steady state photoelectronic analysis in TlInSe2 crystals
QASRAWI, ATEF FAYEZ HASAN; Hasanlı, Nızamı (Elsevier BV, 2011-08-01)
The temperature and illumination effects on the transient and steady state photoconductivities of TlInSe2 crystals have been studied. Namely, two recombination centres located at 234 and at 94 meV and one trap center located at 173 meV were determined from the temperature-dependent steady state and transient photoconductivities, respectively. The illumination dependence of photoconductivity indicated the domination of sublinear and supralinear recombination mechanisms above and below 160 K, respectively. Th...
TORSIONAL VIBRATIONS OF LAYERED COMPOSITE PARABOLOIDAL SHELLS
Kayran, Altan (Elsevier BV, 1990-09-08)
An analysis is presented for the torsional vibration characteristics of layered composite paraboloidal shells. The conditions for the uncoupling of the torsional modes from the bending and extensional modes are first determined for a layered shell of revolution. A finite difference scheme is developed for the solution of the resulting governing equation for the uncoupled torsional frequencies. The results of the finite difference solution for the paraboloids are compared with the analytical solution of unco...
Citation Formats
M. Vanierschot, J. S. Mueller, M. Sieber, M. Perçin, B. W. van Oudheusden, and K. Oberleithner, “Single- and double-helix vortex breakdown as two dominant global modes in turbulent swirling jet flow,” JOURNAL OF FLUID MECHANICS, pp. 0–0, 2020, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/42006.