scholarly journals A Study of Recirculating Flow Fields Downstream of a Diverse Range of Axisymmetric Bluff Body Geometries Suitable for Flame Stabilization

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 339
Author(s):  
Georgios Paterakis ◽  
Konstantinos Souflas ◽  
Andreas Naxakis ◽  
Panayiotis Koutmos
Keyword(s):  
Bluff Body ◽  
Flame Stabilization ◽  
Near Wake ◽  
Diverse Range ◽  
Piv Measurements ◽  
Recirculating Flow ◽  
Image Velocimetry ◽  
Flow Field Characteristics ◽  
Body Shapes ◽  
The Impact

This work investigates the non-reacting time averaged and fluctuating flow field characteristics downstream of a variety of axisymmetric baffles, operating in combination with an upstream double-cavity premixer arrangement. The study aims to broaden knowledge with respect to the impact of different bluff body shapes, leading and trailing edge flow contours, blockage ratios and incoming flow profiles impinging on the bluff body, on the development and properties of the downstream recirculating wake. Particle Image Velocimetry (PIV) measurements have been employed to obtain the mean and turbulent velocity fields throughout the centrally located recirculation zone and the adjacent developing toroidal shear layer. The results are helpful in demarcating the cold flow structure variations in the near wake of the examined baffles which support and, to some extent, determine the flame anchoring performance and heat release disposition in counterpart reacting configurations. Additionally, such results could also assist in the selection of the most suitable flame stabilization configuration for fuels possessing challenging combustion behavior such as multi-component heavier hydrocarbons, biofuels, or hydrogen blends.

Effects of Reacting Conditions on Flow Fields in a Swirl Stabilized Lean Premixed Can Combustor

2018 ◽  
Author(s):  
Suhyeon Park ◽  
Siddhartha Gadiraju ◽  
Jaideep Pandit ◽  
Srinath Ekkad ◽  
Federico Liberatore ◽  
...  
Keyword(s):  
Test Section ◽  
Atmospheric Condition ◽  
Jet Impingement ◽  
Swirl Flow ◽  
Reacting Flows ◽  
Flame Stabilization ◽  
Piv Measurements ◽  
Fuel Nozzle ◽  
Proper Orthogonal ◽  
The Impact

PIV measurements to understand the flow differences between reacting and non-reacting conditions were conducted in an optically accessible single can combustor. An industrial fuel nozzle was installed at the inlet of the test section to generate the swirl flow for flame stabilization and simulate realistic conditions of a gas turbine combustor. Five different equivalence ratios between 0.50 and 0.75 were tested with propane as fuel. Main air flow was also varied from Reynolds number from 50000 to 110000 with respect to the fuel nozzle diameter. Effect of preheating was tested by changing inlet air temperature from 23 to 200°C. The pressure at the test section was close to atmospheric condition throughout the tests. The measurements were performed with a 2-D PIV system. Time-averaged flow velocity, vorticity and turbulent kinetic energy (TKE) were obtained from PIV data and flow structures under different conditions were compared. Swirl jet impingement location on the liner wall was determined as well to understand the impact on the liner wall. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows.

scholarly journals Vortex Phase-Jitter in Acoustically Excited Bluff Body Flames

2009 ◽  
Vol 1 (3) ◽  
pp. 365-387 ◽  
Author(s):  
Santosh J. Shanbhogue ◽  
Michael Seelhorst ◽  
Tim Lieuwen
Keyword(s):  
Heat Release ◽  
Bluff Body ◽  
Axial Direction ◽  
Harmonic Excitation ◽  
Acoustic Excitation ◽  
Phase Jitter ◽  
Image Velocimetry ◽  
Flow Field Characteristics ◽  
Spatially Periodic ◽  
Phase Phase

This paper describes an experimental study of the effect of acoustic excitation on bluff body stabilized flames, specifically on the flow field characteristics. The Kelvin-Helmholtz (KH) instability of the shear layer is excited due to the incident acoustics. In turn, the KH instability imposes a convecting, harmonic excitation on the flame, which leads to spatially periodic flame wrinkling and heat-release oscillations. Understanding the factors influencing these heat release oscillations requires an understanding of the generation, convection, and dissipation of these vortical disturbances. Phase locked particle image velocimetry was carried out over a range of conditions to characterize the vortical dynamics. It was found that the vortex core location exhibits “phase jitter”, manifested as cycle-to-cycle variation in flame and vorticity field at the same excitation phase. Phase jitter is shown to be a function of separation point dynamics, downstream convection time, and amplitude of acoustic excitation. It leads to fairly significant differences between instantaneous and ensemble averaged flow fields and, in particular, the decay rate of the vorticity in the axial direction.

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

1994 ◽  
Author(s):  
Z. Gu ◽  
M. A. R. Sharif
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Flame Stabilization ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Combustion Chambers ◽  
Recirculating Flow ◽  
Conservative Form ◽  
Curvilinear Grid ◽  
Predictor Corrector

Abstract The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

scholarly journals Bluff body drag manipulation using pulsed jets and Coanda effect

2016 ◽  
Vol 805 ◽  
pp. 422-459 ◽  
Author(s):  
Diogo Barros ◽  
Jacques Borée ◽  
Bernd R. Noack ◽  
Andreas Spohn ◽  
Tony Ruiz
Keyword(s):  
Bluff Body ◽  
Three Dimensional ◽  
Base Pressure ◽  
Coanda Effect ◽  
Wake Time ◽  
Recirculating Flow ◽  
Flow Deviation ◽  
Coandǎ Effect ◽  
And Control ◽  
The Impact

The impact of fluidic actuation on the wake and drag of a three-dimensional blunt body is investigated experimentally. Jets blowing tangentially to the main flow force the wake with variable frequency and amplitude. Depending on the forcing conditions, two flow regimes can be distinguished. First, in the case of broadband actuation with frequencies comprising the natural wake time scale, the convection of the jet structures enhances wake entrainment, shortens the length of the recirculating flow and increases drag. Secondly, at higher actuation frequencies, shear-layer deviation leads to fluidic boat tailing of the wake. It additionally lowers its turbulent kinetic energy thus reducing the entrainment of momentum towards the recirculating flow. The combination of both mechanisms produces a rise in the base pressure and reduces the drag of the model. Both actuation regimes are characterized by complementary velocity, pressure and drag measurements at several upstream conditions and control parameters. By adding curved surfaces to deviate the jets by the Coanda effect, periodic actuation is reinforced and drag reductions of approximately 20 % are achieved. The unsteady Coanda blowing not only intensifies the flow deviation and the base pressure recovery but also preserves the unsteady high-frequency forcing effect on the turbulent field. The present results encourage further development of fluidic control to improve the aerodynamics of road vehicles and provide a complementary insight into the relation between wake dynamics and drag.

Methods for the Extraction and Analysis of the Global Mode in Swirling Jets Undergoing Vortex Breakdown

2016 ◽  
Author(s):  
Lothar Rukes ◽  
Moritz Sieber ◽  
C. Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Vortex Breakdown ◽  
Control Strategies ◽  
Combustion Process ◽  
Flame Stabilization ◽  
Global Mode ◽  
Swirling Jets ◽  
Precessing Vortex Core ◽  
Finite Time Lyapunov Exponent ◽  
Image Velocimetry ◽  
The Impact

Swirling jets undergoing vortex breakdown are widely used in combustion applications, due to their ability to provide aerodynamic flame stabilization. It is well known that vortex breakdown is accompanied by a dominant coherent structure, the so called precessing vortex core (PVC). Reports on the impact of the PVC on the combustion process range from beneficial to detrimental. In any event, efficient methods for the analysis of the PVC help to increase the benefit or reduce the penalty resulting from it. This study uses Particle Image Velocimetry (PIV) measurements of a generic non-isothermal swirling jet to demonstrate the use of advanced data analysis techniques. In particular, the Finite Time Lyapunov Exponent (FTLE) and local linear stability analysis (LSA) are shown to reveal deep insight into the physical mechanisms that drive the PVC. Particularly, it is demonstrated that the PVC amplitude is strongly reduced, if heating is applied at the wavemaker of the flow. These techniques are complemented by the traditionally used Proper Orthogonal Decomposition (POD) and spatial correlation techniques. It is demonstrated how these methods complement each other and lead to a comprehensive understanding of the PVC that lays out the path to efficient control strategies.

The influence of the geometry of V-gutter bluff body on transient vortex shedding

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Luckachan K George ◽  
Raja Sekar K ◽  
Srikrishnan A R ◽  
Kannan R
Keyword(s):  
Vortex Shedding ◽  
High Speed ◽  
Bluff Body ◽  
Vortex Motion ◽  
Flame Stabilization ◽  
Cold Flow ◽  
Transient Simulations ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Impact

Abstract This study investigates the turbulent flow field downstream of V-gutters using unsteady numerical modelling. An important domain of application of the vortex shedding induced by the V-gutters is the flame stabilization in high speed combustion systems which find extensive applications in aerospace engineering. In view of this, the present study analyses the impact of the V-gutter geometry, as characterized by the included angle, on inducing vortex motion in the wake. Transient simulations are carried out for three values of the semi-span angle, α = 30°, 45° and 60°. Based on the analysis of the saddle point and the vortex shedding frequency, the study shows that an increase in span angle within this range, favours the effectiveness of the method in flame stabilization. Though the simulations are done for cold flow, the dominant mechanism of vortex shedding is adequately addressed in the analysis.

PIV measurements in near-wake turbulent regions

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840026 ◽  
Author(s):  
Wei-Cheng Chen ◽  
Keh-Chin Chang
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Interrogation Window ◽  
Gray Level ◽  
Flow Properties ◽  
Near Wake ◽  
Piv Measurements ◽  
Optical Diagnostic ◽  
Piv Measurement ◽  
Image Velocimetry

Particle image velocimetry (PIV) is a non-intrusive optical diagnostic and must be made of the seedings (foreign particles) instead of the fluid itself. However, reliable PIV measurement of turbulence requires sufficient numbers of seeding falling in each interrogation window of image. A gray-level criterion is developed in this work to check the attainment of statistically stationary status of turbulent flow properties. It is suggested that the gray level of no less than 0.66 is used as the threshold for reliable PIV measurements in the present near-wake turbulent regions.

Vortex Shedding in a Linear Shear Flow From a Vibrating Marine Cable With Attached Bluff Bodies

1985 ◽  
Vol 107 (1) ◽  
pp. 61-66 ◽  
Author(s):  
R. D. Peltzer ◽  
D. M. Rooney
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Bluff Bodies ◽  
Near Wake ◽  
Cable System ◽  
Sheared Flow ◽  
Linear Shear ◽  
Body Shapes ◽  
Marine Cable

The present study examines the vortex street wake behavior of a flexible, helically wound, high aspect ratio marine cable in a linear shear flow. Particular attention is paid to the lock-on phenomena associated with uniform and sheared flow past the cable when it is forced to vibrate in the first mode, normal to the flow. An analysis is given of the effects on the vortex shedding and synchronization phenomena that are generated by placing distributions of spherical bluff body shapes along the span of the cable in uniform and sheared flow. The latter geometry is representative of a number of cable system deployments and has special consequencies for strumming in a shear flow. The effectiveness of these attached spheres as strumming-suppression devices is evaluated. Synchronized vibration and/or the presence of the bluff bodies significantly affected the spanwise character of the near wake cellular vortex shedding structure. The spanwise extent of the resonant, vortex-excited oscillations was significantly extended by the presence of the spheres along the cable span. This finding was particularly significant because it meant that the undesirable effects that accompanied synchronization would be extended over a longer portion of the cable span.

Large Eddy Simulations of Static and Rotating Ribbed Channels in Adiabatic and Isothermal Conditions

2017 ◽  
Author(s):  
Thomas Grosnickel ◽  
Florent Duchaine ◽  
Laurent Y. M. Gicquel ◽  
Charlie Koupper
Keyword(s):  
Flow Direction ◽  
Secondary Flows ◽  
Flow Topology ◽  
Time Resolved ◽  
Piv Measurements ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Rib Turbulators ◽  
The Impact

In an attempt to better understand spatially developing rotating cooling flows, the present study focuses on a computational investigation of a straight, rotating rib roughened cooling channel initially numerically studied by Fransen et al. [1]. The configuration consists of a squared channel equipped with 8 rib turbulators placed with an angle of 90 degrees with respect to the flow direction. The rib pitch-to-height (p/h) ratio is 10 and the height-to-hydraulic diameter (h/Dh) ratio is 0.1. The simulations are based on a case where time resolved two-dimensional Particle Image Velocimetry (PIV) measurements have been performed at the Von Karman Institute (VKI) in a near gas turbine operating condition: the Reynolds number (Re) and the rotation number (Ro) are around 15000 and ± 0.38 respectively. Adiabatic as well as anisothermal conditions have been investigated to evaluate the impact of the wall temperature on the flow, especially in the rotating configurations. Static as well as both positive and negative rotating channels are compared with experimental data. In each case, either an adiabatic or an isothermal wall boundary condition can be computed. In this work, Large Eddy Simulation (LES) results show that the high fidelity CFD model manages very well the turbulence increase (decrease) around the rib in destabilizing (stabilizing) rotation of the ribbed channels. Thanks to the full spatial and temporal description produced by LES, the spatial development of secondary flows are found to be at the origine of observed differences with experimental measurements. Finally, the model is also able to reproduce the differences induced by buoyancy on the flow topology in the near rib region and resulting from an anisothermal flow in rotation.

The Blockage Effects for the Unsteady Characteristics of the Near Wake Flows Behind a Bluff Body

2003 ◽  
Author(s):  
Hiroshi Nakayama ◽  
Masafumi Hirota ◽  
Hiroshi Yamashita ◽  
Yoshio Fukui ◽  
Hideomi Fujita
Keyword(s):  
Bluff Body ◽  
Particle Image ◽  
Flow Characteristics ◽  
Measured Data ◽  
Near Wake ◽  
Number Range ◽  
Wake Flows ◽  
Image Velocimetry ◽  
Unsteady Characteristics ◽  
Proper Orthogonal

Unsteady flow characteristics behind a triangular-shaped bluff body were experimentally investigated in a water flow of the Reynolds number range ReD = 500∼3000. The effect of changing the blockage ratio, BR, from BR = 0.2 to 0.6, was investigated. The experimental data of the velocity were obtained by using cinematic particle image velocimetry (PIV) to map the unsteady velocity field around the vortex-generating region. Based on the measured data, influences of the blockage on time-averaged velocities, turbulence intensity distributions and Strouhal number were examined. Moreover, proper orthogonal decomposition (POD) was performed on fluctuating vorticity fields to identify the most energetic parts of the vorticity fluctuations.

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