scholarly journals Effect of Nozzle Confinement in the Axial Swirler

2019 ◽  
Vol 196 ◽  
pp. 00032
Author(s):  
Roman Yusupov ◽  
Ivan Litvinov ◽  
Sergey Shtork
Keyword(s):  
Unsteady Flow ◽  
Strouhal Number ◽  
Vortex Core ◽  
Recirculation Zone ◽  
Averaging Method ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Secondary Vortex ◽  
Precessing Vortex Core ◽  
Swirl Parameter

This work is devoted to the study of unsteady flow with the precessing vortex core (PVC) formed at the exit of a compact vane swirler with varying vanes angle and nozzles diameters. Amplitude-frequency characteristics of the PVC were obtained using two microphones. The modified Strouhal number dependence have showed a good generalization of the data for all nozzle diameters. The averaged and phase-averaged distributions of three components of velocity have been measured via the LDA system. The increasing the recirculation zone at increasing nozzle diameter for the swirl parameter Sg=0.53 and Re=1.5·104 was detected. The degeneration of PVC was detected for all studied nozzle diameters D = 30, 40, 50 mm. In case of smallest diameter D = 30 mm the PVC ceases to be periodic due to the absence of a recirculation zone. The three-dimensional structure of the PVC is reconstructed by the phase averaging method and visualized using the Q-criterion. Formation of the shifted recirculation zone, outer secondary vortex (OSV) and inner secondary vortex (ISV) is observed.

scholarly journals The unsteady swirling jet in a model of radial burner

2021 ◽  
Vol 2119 (1) ◽  
pp. 012106
Author(s):  
I V Litvinov ◽  
E U Gorelikov ◽  
S I Shtork
Keyword(s):  
Experimental Study ◽  
Unsteady Flow ◽  
Strouhal Number ◽  
Vortex Core ◽  
Guide Vane ◽  
Swirl Flow ◽  
Acoustic Sensors ◽  
Swirl Number ◽  
Precessing Vortex Core ◽  
Vane Angle

Abstract The experimental study of an isothermal swirl flow with the formation of a precessing vortex core in the radial swirler upon non-confinement and confinement conditions is carried out. Velocity profiles are obtained with varying Re and guide vane angle, changing the swirl number S. Four acoustic sensors and LDA system are used to measure Strouhal number as the function of the integral swirl number in the range from 0.5 <S <0.8. It is shown that the unsteady flow with PVC effect significantly changes upon non-confinement and confinement conditions.

scholarly journals The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel

2008 ◽  
Vol 603 ◽  
pp. 331-365 ◽  
Author(s):  
JAMES H. J. BUCHHOLZ ◽  
ALEXANDER J. SMITS
Keyword(s):  
Aspect Ratio ◽  
Strouhal Number ◽  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Dimensional Structure ◽  
Peak Efficiency ◽  
Thrust Coefficient ◽  
Wake Structure ◽  
Thrust Performance

Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For ReC = O(104), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9% and 21% were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and digital particle image velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes was investigated in detail for AR = 0.54, A/S = 0.31 and ReC = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5, an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is robust with variation in Reynolds number and is consistent with structures observed for a wide variety of unsteady flows. Movies are available with the online version of the paper.

Characterisation of acoustically linked oscillations in cyclone separators

2015 ◽  
Vol 780 ◽  
pp. 45-59 ◽  
Author(s):  
T. A. Grimble ◽  
A. Agarwal
Keyword(s):  
Strouhal Number ◽  
Vortex Core ◽  
Internal Flow ◽  
Simple Relationship ◽  
Swirl Number ◽  
Precessing Vortex Core ◽  
Scaling Parameters ◽  
Invasive Method ◽  
Dimensional Parameters ◽  
Flow Oscillations

The hydrodynamic oscillations of a cyclone separator – in particular the precessing vortex core (PVC) phenomena – are investigated by measuring their radiated sound spectra. Strong coherence was observed between internal flow oscillations measured via hot wire anemometry and the external acoustic field measured via microphone. This means that the oscillations can be characterised by using acoustics as a proxy. The oscillations cause narrow-band noise, referred to as cyclone hum. System characterisation by dimensional analysis used velocity and length scales of the vortex core region as scaling parameters. The relevant non-dimensional parameters are a Strouhal number for the cyclone hum centre frequency, a Reynolds number, a geometry based swirl number and numerous geometric scales defining the shape of the device. Cyclones with multiple sizes of inlets and outlets were tested at different flow rates using external microphones to detect the cyclone hum. The results produce an excellent collapse of the data, yielding a simple relationship for Strouhal number as a function of swirl number and the outlet diameter ratio. The non-invasive method of examining oscillations that is presented in this paper could be applied to other swirling systems.

Effect of the Precessing Vortex Core on Primary Atomization

2015 ◽  
Vol 229 (6) ◽  
Author(s):  
Enrico Bärow ◽  
Sebastian Gepperth ◽  
Rainer Koch ◽  
Hans-Jörg Bauer
Keyword(s):  
Liquid Film ◽  
Vortex Core ◽  
High Speed ◽  
Recirculation Zone ◽  
Film Flow ◽  
Combustion Chambers ◽  
Precessing Vortex Core ◽  
Swirl Flows ◽  
Liquid Film Flow ◽  
Pod Analysis

AbstractThe present work is focused on the airblast atomization in a gas turbine model combustor. Swirl flows in such combustion chambers form an inner recirculation zone that can develop a precessing vortex core. This instability affects the velocity field at the exit of the nozzle, where the fuel is atomized. The influence of the precessing vortex core on the airblast atomization is examined in this work. The flow field in the combustion chamber is examined under reacting and non-reacting conditions. The velocity amplitudes under reacting conditions are more than twice as high compared to non-reacting conditions. The influence of the precessing vortex core on the airblast atomization process is examined in detail at an atomization test rig with a perspex nozzle. High speed shadowgraphy and POD analysis have been performed of the liquid film on the prefilmer as well as on the ligaments formed at the atomizing edge. It was observed that although the PVC does affect the liquid film flow of the prefilming surface, it does not affect the breakup into ligaments, i. e. primary atomization.

Alternate Eddy Shedding Set Up by the Nonaxisymmetric Recirculation Zone at the Exhaust of a Cyclone Dust Separator

1998 ◽  
Vol 120 (1) ◽  
pp. 193-199 ◽  
Author(s):  
A. J. Griffiths ◽  
P. A. Yazdabadi ◽  
N. Syred
Keyword(s):  
Recirculation Zone ◽  
Laser Doppler Anemometry ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Time Dependent ◽  
Velocity Measurements ◽  
Flow Zone ◽  
Precessing Vortex Core ◽  
Dust Separator ◽  
Set Up

Two cyclone dust separators with geometric swirl numbers of 3.324 and 3.043 were used to analyze the motion of the complex three-dimensional time dependent motion set up in the free exhaust. A quantitative analysis of the flow was carried out, obtaining time dependent velocity measurements with the use of laser Doppler anemometry (L.D.A.) techniques. The investigations highlighted a eddy or vortex shedding mechanism in two distinct areas of the flow. This was in part caused by a reverse flow zone and a precessing vortex core within the exhaust region of the separator. Changes in the Reynolds number by a factor of 2 were observed to have no effect on the main characteristics of the flow. Some changes were seen in the flow structure with change in swirl number, particularly the size of the reverse flow zone and the position of the large engulfment vortices.

scholarly journals Lattice gas automaton modelling of a vortex flow meter: Strouhal–Reynolds number dependence

2017 ◽  
Vol 56 (4) ◽  
pp. 191-199
Author(s):  
Vaidas Juknevičius ◽  
Jogundas Armaitis
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Vortex Flow ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Flow Meter ◽  
Reynolds Number Dependence

Motivated by recent experimental and computational results concerning a three-dimensional structure of vortices behind a vortex shedding flow meter [M. Reik et al., Forsch. Ingenieurwes. 74, 77 (2010)], we study the Strouhal–Reynolds number dependence in the vortex street in two dimensions behind a trapezoid-shaped object by employing two types of Frisch–Hasslacher–Pomeau (FHP) models. Our geometry is intended to reproduce the operation of a vortex shedding flow meter in a two-dimensional setting, thus preventing the formation of a three-dimensional vortex structure. In particular, we check if the anomalous Reynolds–Strouhal number dependence reported for three dimensions can also be found in our two-dimensional simulation. As we find that the Strouhal number is nearly independent of the Reynolds number in this particular setup, our results provide support for the hypothesis that three-dimensional flow structures are responsible for that dependence, thus hinting at the importance of the pipe diameter to the accurate operation of industrial vortex flow meters.

The Interaction of the Precessing Vortex Core and Reverse Flow Zone in the Exhaust of a Swirl Burner

1994 ◽  
Vol 208 (1) ◽  
pp. 27-36 ◽  
Author(s):  
N Syred ◽  
T O'Doherty ◽  
D Froud
Keyword(s):  
Vortex Core ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Basic Structure ◽  
Flow Zone ◽  
Three Dimensional Flow ◽  
Laser Anemometry ◽  
Precessing Vortex Core ◽  
First Time

This paper describes recent work at Cardiff to gain further understanding of the fundamental processes occurring in swirl burners. The phenomenon of the precessing vortex core has been characterized via the use of a two-component laser anemometry system and the signal from a hot-wire anemometry probe for triggering purposes. This has allowed the rotating three-dimensional flow associated with the precessing vortex core to be characterized for the first time at different downstream sections. Regions of reversed mean tangential velocity have been identified while new insights into the basic structure of the reverse flow zone have been provided.

Experimental and Numerical Investigation of the Unsteady Flow Field and Tone Generation in an Isolated Centrifugal Fan Impeller

2011 ◽  
Author(s):  
Daniel Wolfram ◽  
Thomas H. Carolus
Keyword(s):  
Unsteady Flow ◽  
Numerical Investigation ◽  
Vortex Core ◽  
Large Range ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Centrifugal Fan ◽  
Helical Vortex ◽  
The One ◽  
Tone Generation

In spite of low circumferential Mach number the sound of isolated centrifugal fan impellers is sometimes dominated by distinctive tones at blade passing frequency (BPF) and integer multiples. This paper reports on an experimental and numerical investigation intended to unveil the tone generating mechanism. The sound spectra from three impellers operating at a large range of speed were measured and decomposed into Strouhal and Helmholtz number dependent functions. This led to the preliminary conclusion that the BPF related tones are exclusively flow-induced. Based on hot-wire and blade pressure fluctuation measurements and a subsequent correlation analysis, coherent flow structures different from the one associated with the principal azimuthal flow pattern due to the blades were detected. Eventually, numerical three-dimensional unsteady flow simulation and experimental flow visualization revealed an inlet vortex. It takes on a helical form, with the vortex core slowly varying its position with respect to the impeller center. As the blades cut through that quasi-stationary helical vortex they encounter blade force fluctuations producing the BPF tones. The slow spin of the vortex core and the slow variation of vortex strength were identified as the reason for the amplitude modulation of the BPF tone.

LES of Turbulent Swirling Jets: Study of Jet Precession, Recirculation and Vortex Breakdown

2009 ◽  
Author(s):  
Ranga Dinesh ◽  
Karl Jenkins ◽  
Michael Kirkpatrick
Keyword(s):  
Vortex Core ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Vortex Breakdown ◽  
Low Frequency ◽  
Test Case ◽  
Test Cases ◽  
Swirl Number ◽  
Eddy Viscosity Model ◽  
Precessing Vortex Core

Large eddy simulations (LES) of turbulent isothermal swirling flows have been investigated. The Sydney swirl burner configuration has been used for all simulated test cases from a low to a high swirl and Reynolds numbers. Four test cases based on different swirl numbers have been considered and the influence of the swirl number for producing recirculation, vortex breakdown, precession vortex core and the precession frequencies have been investigated. The governing equations for the continuity and momentum are solved on a structured Cartesian grid, and a Smagorinsky eddy viscosity model with the localised dynamic procedure is used as the subgrid scale turbulence model. The results show that the LES successfully predicts both the upstream first recirculation zone generated by the bluff body and the downstream vortex breakdown bubble (VBB) induced by swirl. The plots reveal that the expansion of the upstream recirculation zone is almost similar for each test case. LES results revealed that the increasing swirl number affect to form the VBB in the downstream region, however it promotes the shear layer instability in the recirculation zones. The frequency spectrums indicate the presence of low frequency oscillations and the existence of a central jet precession. Results demonstrated distinct precession frequencies at the considered spatial jet locator and agreed well with the experimental values. The results also highlight the formation of a precessing vortex core (PVC).

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