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

2016 ◽  
Vol 57 ◽  
pp. 214-230 ◽  
Author(s):  
T. Luginsland ◽  
F. Gallaire ◽  
L. Kleiser
Keyword(s):  
Vortex Breakdown ◽  
Jet Flows ◽  
Swirling Jet

Stochastic-Based RANS-LES Simulations of Swirling Turbulent Jet Flows

2017 ◽  
Vol 18 (5) ◽  
pp. 351-369 ◽  
Author(s):  
Michael K. Stoellinger ◽  
Stefan Heinz ◽  
Celestin P. Zemtsop ◽  
Harish Gopalan ◽  
Reza Mokhtarpoor
Keyword(s):  
Vortex Breakdown ◽  
Hybrid Methods ◽  
Turbulent Jet ◽  
Jet Flows ◽  
Flow Simulations ◽  
Swirling Jet ◽  
Les Model ◽  
Sound Theoretical Basis ◽  
Better Than ◽  
Good Agreement

AbstractMany turbulent flow simulations require the use of hybrid methods because LES methods are computationally too expensive and RANS methods are not sufficiently accurate. We consider a recently suggested hybrid RANS-LES model that has a sound theoretical basis: it is systematically derived from a realizable stochastic turbulence model. The model is applied to turbulent swirling and nonswirling jet flow simulations. The results are shown to be in a very good agreement with available experimental data of nonswirling and mildly swirling jet flows. Compared to commonly applied other hybrid RANS-LES methods, our RANS-LES model does not seem to suffer from the ’modeled-stress depletion’ problem that is observed in DES and IDDES simulations of nonswirling jet flows, and it performs better than segregated RANS-LES models. The results presented contribute to a better physical understanding of swirling jet flows through an explanation of conditions for the onset and the mechanism of vortex breakdown.

Turbulence Model Upgrades for Swirling Flows

2007 ◽  
Author(s):  
J. D. Chenoweth ◽  
B. York ◽  
A. Hosangadi
Keyword(s):  
Turbulence Model ◽  
Richardson Number ◽  
Vortex Breakdown ◽  
Azimuthal Velocity ◽  
Operating Conditions ◽  
Jet Flows ◽  
Data Sets ◽  
Mixing Rate ◽  
Jet Mixing ◽  
Swirling Jet

The ability to accurately model axisymmetric, turbulent swirling jet flows over a variety of inflow conditions is evaluated. The deficiency of the standard k-ε turbulence model in predicting mixing rates in flows with streamline curvature is well known. A relatively straightforward modification to this model is made based on a local value of the flux Richardson number which accounts for the azimuthal velocity and its variation. To evaluate the effectiveness of this modification two different experimental data sets are used to compare the computational results against. All calculations were performed using the structured, density based, CRAFT CFD® code utilizing a preconditioning methodology. Both cases have initial swirl distributions that are equivalent to a solid-body rotation profile, and have swirl numbers that are low enough to remain below the vortex breakdown regime. They also have non-swirling jet data available for the same geometries and operating conditions which allows the increased jet mixing rate of swirling jets over purely axial jets to be confirmed. All calculations showed a significant improvement of centerline velocity decay as well as downstream radial velocity profiles when the Richardson number correction was activated. For the case with turbulence data, the centerline decay of turbulent kinetic energy was also much improved. An important result that was discovered was the extreme sensitivity of the downstream evolution of the jet to the specification of the initial k and ε profiles, highlighting the critical need for a comprehensive experimental characterization of all flow properties at the jet exit.

The Effects of Exit Boundary Condition on Precessing Vortex Core Dynamics

2019 ◽  
Author(s):  
Danielle Mason ◽  
Sean Clees ◽  
Mark Frederick ◽  
Jacqueline O’Connor
Keyword(s):  
Boundary Condition ◽  
Vortex Core ◽  
Gas Turbines ◽  
Vortex Breakdown ◽  
Base Flow ◽  
Eigenvalue Decomposition ◽  
Precessing Vortex Core ◽  
Swirling Jet ◽  
Exit Boundary ◽  
The Impact

Abstract Many industrial combustion systems, especially power generation gas turbines, use fuel-lean combustion to reduce NOx emissions. However, these systems are highly susceptible to combustion instability, the coupling between combustor acoustics and heat release rate oscillations of the flame. It has been shown in previous work by the authors that a precessing vortex core (PVC) can suppress shear layer receptivity to external perturbations, reducing the potential for thermoacoustic coupling. The goal of this study is to understand the effect of combustor exit boundary condition on the flow structure of a swirling jet to increase fundamental understanding of how combustor design impacts PVC dynamics. The swirling jet is generated with a radial-entry, variable-angle swirler, and a quartz cylinder is fixed on the dump plane for confinement. Combustor exit constriction plates of different diameters are used to determine the impact of exit boundary condition on the flow field. Particle image velocimetry (PIV) is used to capture the velocity field inside the combustor. Spectral proper orthogonal decomposition, a frequency-resolved eigenvalue decomposition that can identify energetic structures in the flow, is implemented to identify the PVC at each condition in both energy and frequency space. We find that exit boundary diameter affects both the structure of the flow and the dynamics of the PVC. Higher levels of constriction (smaller diameters) force the downstream stagnation point of the vortex breakdown bubble upstream, resulting in greater divergence of the swirling jet. Further, as the exit diameter decreases, the PVC becomes less energetic and less spatially defined. Despite these changes in the base flow and PVC coherence, the PVC frequency is not altered by the exit boundary constriction. These trends will help inform our understanding of the impact of boundary conditions on both static and dynamic flame stability.

A swirling jet with vortex breakdown: three-dimensional coherent structures

2016 ◽  
Vol 23 (2) ◽  
pp. 301-304 ◽  
Author(s):  
S. V. Alekseenko ◽  
V. M. Dulin ◽  
M. P. Tokarev ◽  
D. M. Markovich
Keyword(s):  
Coherent Structures ◽  
Vortex Breakdown ◽  
Three Dimensional ◽  
Swirling Jet

Three-dimensional coherent structures in a swirling jet undergoing vortex breakdown: stability analysis and empirical mode construction

2011 ◽  
Vol 679 ◽  
pp. 383-414 ◽  
Author(s):  
K. OBERLEITHNER ◽  
M. SIEBER ◽  
C. N. NAYERI ◽  
C. O. PASCHEREIT ◽  
C. PETZ ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Coherent Structures ◽  
Vortex Breakdown ◽  
Particle Image Velocimetry Data ◽  
Turbulent Shear ◽  
Mean Flow ◽  
Helical Structures ◽  
Global Mode ◽  
Swirling Jet ◽  
Time Periodic

The spatio-temporal evolution of a turbulent swirling jet undergoing vortex breakdown has been investigated. Experiments suggest the existence of a self-excited global mode having a single dominant frequency. This oscillatory mode is shown to be absolutely unstable and leads to a rotating counter-winding helical structure that is located at the periphery of the recirculation zone. The resulting time-periodic 3D velocity field is predicted theoretically as being the most unstable mode determined by parabolized stability analysis employing the mean flow data from experiments. The 3D oscillatory flow is constructed from uncorrelated 2D snapshots of particle image velocimetry data, using proper orthogonal decomposition, a phase-averaging technique and an azimuthal symmetry associated with helical structures. Stability-derived modes and empirically derived modes correspond remarkably well, yielding prototypical coherent structures that dominate the investigated flow region. The proposed method of constructing 3D time-periodic velocity fields from uncorrelated 2D data is applicable to a large class of turbulent shear flows.

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