Unsteady Aspects of Multi-Interacting Swirlers Using POD Analysis

2018 ◽  
Author(s):  
Foad Vashahi ◽  
Shahnaz Rezaei ◽  
Jeekeun Lee
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Low Frequency ◽  
Working Fluid ◽  
Fuel Injector ◽  
Mean Flow ◽  
Stagnation Points ◽  
Wide Range ◽  
Model Chamber ◽  
Pod Analysis

Twin annular premixed swirler known as TAPS by GE has provided an effective solution to generate low NOx combustion by implementing both diffusion and premixed flames. The fuel injector is less susceptible to combustion instabilities owing to its central diffusion flame and eco-friendly due to its radial premixed swirler. To this extent, 2D PIV experiment was conducted on three newly designed triple swirlers to measure their corresponding velocity fields. The swirlers were designed in a way that the inner and intermediate swirlers are axial type, counter-rotating and remained unchanged with three different radial type outer swirlers. The design characteristic swirl numbers of the outer swirlers were 0.5, 1.0 and 1.5, to impose low, medium and intense swirling motion, respectively. The main objective of the current study is to investigate the interaction of the shear layers emerging from the outer swirler with the both inner and intermediate. Air is used as working fluid and experiments were done in confined condition. The study of the mean flow field indicated that the outer swirler dominates the flow field and defines the behavior of the main features such as swirling jet angle, the resultant inner recirculation zone, and the wall stagnation points. Proper Orthogonal Decomposition (POD) analysis showed a wide range of low-frequency modes spread over the entire domain and stated the domination of the outer swirling flow. It was found that an increase in the intensity of the outer swirler contributes to an intensified interaction with the model chamber walls highlighting the significance of the confinement ratio in higher swirl numbers.

Effects of the Interaction Point of Multi-Passage Swirlers on the Swirling Flow Field

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Foad Vashahi ◽  
Jeekeun Lee
Keyword(s):  
Geometrical Parameter ◽  
Swirling Flow ◽  
Energy Levels ◽  
Fuel Mixture ◽  
Mean Flow ◽  
Interaction Point ◽  
Stagnation Points ◽  
Image Velocimetry ◽  
The Mean ◽  
Proper Orthogonal

An experimental study is conducted to understand the mean and instantaneous behavior of the swirling flow issued from a triple swirler influenced by a single critical geometrical parameter, termed as the passage length. The investigated geometrical parameter defines the interaction point of the inner axial swirlers with the outer radial swirler, which consequently defines the primary air–fuel mixture characteristics and the resultant combustion state. Experiments were performed under cold flow conditions, and planar particle image velocimetry was employed to measure the velocity field. The mean flow pattern exhibited significant differences in terms of the swirl-jet width and angle and altered the number of stagnation points on the swirler axis. When the passage length was reduced to half, two stagnation points appeared on the swirler axis due to an initially developed smaller recirculation zone at the swirler mouth. Also, the turbulent activity at the vicinity of the swirler increased with as the passage length reduced. Investigations on the relocation of the second stagnation point on the axis through an arbitrary window revealed identical standard deviation in x and y directions. The energetic coherent structures extracted from the proper orthogonal decomposition also identified major differences in terms of the spatial distribution of the modes and their corresponding energy levels. The experimental results indicated that if the passage length is altered, the number of stagnation points on the swirler axis increases, and a breakdown of both the bubble and cone vortex may appear at the same time as different energy levels.

The Impact of Representative Aerodynamic Flow Fields on Liquid Fuel Atomisation in Modern Gas Turbine Fuel Injectors

2014 ◽  
Author(s):  
A. G. Barker ◽  
J. F. Carrotte
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Liquid Fuel ◽  
Swirling Flow ◽  
Subsequent Development ◽  
Potential Effect ◽  
Far Field ◽  
Fuel Injector ◽  
Swirl Vane ◽  
The Impact

In modern gas turbine engines swirl is typically imparted to the airflow as it enters the region of heat release to stabilize the flame. This swirling airstream is often highly turbulent and contains non-uniformities such as swirl vane wakes. However, it is within this environment that fuel atomization takes place. This paper is concerned with the potential effect of these airstream characteristics on the atomization process. Such a flow field is difficult to capture within simplified geometries and so measurements have been made within, and downstream of, injector representative geometries. This is experimentally challenging and required the application of a variety of techniques. The geometry considered is thought typical of an air-blast style injector, as may be used within current or future applications, whereby liquid fuel is introduced onto a pre-filming surface over which an airstream passes. Data is presented which characterizes the atomizing airstream presented to the pre-filming region. This includes significant flow field non-uniformities and turbulence characteristics that are mainly associated with the swirling flow along with the vanes used to impart this swirl. The subsequent development of these aerodynamic features over the pre-filming surface is also captured with, for example, swirl vane wakes being evident through the injector passage and into the downstream flow field. It is argued these characteristics will be common to many injector designs. Measurements with and without fuel indicate the effect of the liquid film, on the non-dimensional aerodynamic flow field upstream of the pre-filming region, is minimal. However, the amount of airflow passing through the pre-filming passage is affected. In addition to characterization of the airstream, its impact on the liquid fuel film and its development along the pre-filming surface is visualized. Furthermore, PDA measurements downstream of the fuel injector (i.e. the injector ‘far-field) are presented and the observed spray characteristics spatially correlated with the upstream aerodynamic atomizing flow field. Hence for the first time a series of experimental techniques have been used to capture and correlate both near and far field atomization characteristics within an engine representative aerodynamic flow field.

Experimental Investigation of Airflow and Spray Stability in an Air-Blast Injector of an Industrial Gas Turbine

2004 ◽  
Author(s):  
Andrei Secareanu ◽  
Dragan Stankovic ◽  
Laszlo Fuchs ◽  
Vladimir Milosavljevic ◽  
Jonas Holmborn
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Swirling Flow ◽  
Laser Sheet ◽  
Front Panel ◽  
Mean Flow ◽  
Air Blast ◽  
Full Cross Section ◽  
Airflow Field ◽  
Industrial Gas Turbine

The airflow field and spray characteristics from an air blast type of injector in an industrial gas turbine (GT) combustor geometry have been investigated experimentally and numerically. The flame in the current combustor is stabilized by a highly swirling flow. The stabilization of the flame is strongly dependent on the stability of the flow field out from the injector and into the combustor. Liquid fuel spray formation in the current type of injector is highly dependent on the airflow from the internal swirler, which supplies the shear to break the liquid film, and form the spray. Experiments were performed in a Perspex model of a 12° sector of the combustor with airflow scaled to atmospheric conditions. The geometry was comprised of the air section including the full primary zone, injector, combustor swirler, front panel and primary air jets. The flow field was visualized using particles that were illuminated by a laser sheet. Quantitative characterization was done using LDA. The airflow field was characterized by the mean flow pattern covering the full cross-section of the flow field and additional long time measurements at a number of locations in order to capture frequency content of the flow. Isothermal spray measurements were performed in an unconfined geometry including the injector, swirl generator and front panel. The spray uniformity was qualitatively investigated using video camera and quantitatively characterized by PDA. The studies of the flow field and fuel atomization (droplet size and density) under different conditions are summarized below.

Geometry Effects on the Flow Field and the Spectral Characteristics of a Triple Annular Swirler

2003 ◽  
Author(s):  
Guoqiang Li ◽  
Ephraim J. Gutmark
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
High Frequency ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Low Frequency ◽  
Tube Length ◽  
Formation Mechanisms ◽  
Recirculation Bubble ◽  
Inlet Conditions

The dynamics of vortex breakdown are important to the performance of gas turbine combustors where swirling flows are extensively used to stabilize the flame and extend the lean flammability limit (LBO). Due to the strong interaction of vortical structures in the swirling flow with heat release and acoustical modes, vortex breakdown mechanism is essential to understanding the thermoacoustic behavior and to the development of combustion instability control strategy. This paper analyzes the vortex breakdown behavior downstream of a Triple Annular Research Swirler (TARS) based on velocity flow field data from stereoscopic PIV measurement and spectral data from hotwire/film measurements. The vortical structure is highly dependent on the different swirler combinations (swirler geometry) as well as on inlet conditions such as air flow-rate, mixing tube length and downstream conditions such as exhaust nozzle contraction ratio. The scale, location, strength, and formation mechanisms of the large-scale vortices vary for different geometries. The shape of the recirculation bubble changes with the outlet boundary conditions, suggesting that the swirling flow inside the combustion chamber remains subcritical downstream of the vortex breakdown. However, spectral analysis reveals that the dominant frequencies close to the exit of the TARS show only slight change for different outlet boundary conditions. Three ranges of frequencies characterize the spectral domain of TARS: high frequency close to the TARS exit, middle range frequency downstream of this region, and low frequency in most regions further downstream. The sources of instabilities in these three regions could be attributed to the strong shear layer, precessing vortex core and interaction between spanwise and azimuthal instabilities. The outlet boundary conditions affect the middle and low frequency range but have no effect on the high frequency. The inlet conditions have global effect on the entire flow region.

An Experimental Characterization of the Interaction Between Two Tandem Planar Jets in a Crossflow

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Kun Zhao ◽  
Patrick N. Okolo ◽  
Yong Wang ◽  
John Kennedy ◽  
Gareth J. Bennett
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Near Field ◽  
Mean Flow ◽  
Piv Measurement ◽  
Jet Trajectory ◽  
The Mean ◽  
Pod Analysis ◽  
Particle Imaging ◽  
Quantitative Definition

This study reports an experimental investigation of two planar jets in a crossflow in a tandem arrangement. Tests were conducted in an open-jet wind tunnel facility using two-dimensional (2D)-particle imaging velocimetry (PIV) measurement. Using the terminology in the dual jets in a quiescent ambient, the mean flow field of the crossflow arrangement was divided into a converging region, a merging region, and a combined region. An approach to determining the range of these three regions was proposed based on the mean characteristics of horizontal velocity profiles of the flow field, validated by the experimental data. The momentum-dominated near field (MDNF) for the rear jet in the dual-jet configuration was recognized using the horizontal offset of mean jet trajectory, which accordingly gives a quantitative definition of the MDNF range. Discussions were made on the effects of different parameters on the three regions and MDNF. Finally, snapshot proper orthogonal decomposition (POD) analysis was conducted, characterizing the coherent structures of the flow field, particularly the large-scale vortices. It was observed that the large-scale vortices mainly occur in the shear layers of the jets and their occurrence is affected by the parameters of the jets. In addition, compared with the single-jet configuration, the introduction of the front jet was found to contribute to the occurrence and development of the large-scale vortices.

Characterization of a Multi-Swirler Fuel Injector Using Simultaneous Laser Based Planar Measurements of Reaction Zone, Flow Field, and Fuel Distribution

2009 ◽  
Author(s):  
P. Iudiciani ◽  
S. M. Hosseini ◽  
R. Zoltan-Szasz ◽  
C. Duwig ◽  
L. Fuchs ◽  
...  
Keyword(s):  
Flow Field ◽  
Flame Stabilization ◽  
Injection System ◽  
Oh Radicals ◽  
Fuel Injector ◽  
Flow Conditions ◽  
Cross Sectional ◽  
Fuel Distribution ◽  
Flame Dynamics ◽  
Wide Range

Modern gas turbine spray combustors feature multiple swirlers with distributed fuel injection system for rapid fuel/air mixing and flame stabilization ensuring low NOx operations. In the present paper, we investigate the effects of different swirler designs on flame characteristics, stabilization, and behavior at lean blow out using a Triple Annular Research Swirler (TARS) burner. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (LIF) of OH radicals indicating the reacting zone, LIF Acetone indicating unburnt fuel distribution and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow dynamics, fuel distribution and flame dynamics for different swirler geometries, air flow rates, and equivalence ratios. Both axial and nearly perpendicular to axis cross-sectional planes were investigated. The three swirler configurations allowed getting stable and repeatable flames over a wide range of different flow and fuel equivalence ratio conditions, confirming the good flexibility and operability of the TARS burner. Averaged fields are presented to compare the effect of different flow conditions using the same swirler configuration, and the effect of different swirler configurations at the same flow conditions. LIF and PIV instantaneous samples are also shown, both in axial and cross sectional planes, with structures captured in detail. Perfect matching is found between unburnt and burnt field, as well as agreement between axial and cross-sectional measurements. Particular attention has been placed on unstable flames and a highly unsteady flame near the lean blow out (LBO) is shown. Local extinctions are occasionally seen on instantaneous snapshots. Unsteadiness of such flame is suitable to exemplify the use of Proper Orthogonal Decomposition (POD) analysis that identifies the most “energetic” large scale structures or modes of the flame. In particular, rotational and helical modes are observed which can contribute to the swirling flame instability. The results show the effect of the strength and rotation direction of the swirlers can lead to strong flame stratification or to a more homogenous flames. Analysis of the flame dynamics, indicates that the flame can be stabilized dynamically without the presence of a Central Recirculation Zone (CRZ) through flame quenching and flame propagation.

Analysis of the Spray and Transfer Function of Swirling Spray Flames From a Multi-Jet Steam Assisted Liquid Fuel Injector

2014 ◽  
Author(s):  
Clément Mirat ◽  
Daniel Durox ◽  
Thierry Schuller
Keyword(s):  
Transfer Function ◽  
Flow Rate ◽  
Transfer Functions ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Low Frequency ◽  
Laser Doppler ◽  
Flow Rate Ratio ◽  
Fuel Injector ◽  
Spray Flames

Characterizations of the response of swirling spray flames to flow rate modulations over the entire frequency range remain scarce. This response is addressed here by determining the transfer function of spray flames stabilized on a multi-jet steam-assisted dodecane injector in a turbulent swirling flow confined by a quartz tube. This type of burner is used in some liquid fueled industrial boilers. In the absence of combustion and air flow, a phase Doppler particle analyzer is used to determine the Sauter mean diameter (SMD) of the fuel spray as a function of the atomizing gas to fuel mass flow rate ratio (GLR) injected in the nozzle. For small values of the GLR, the SMD of the generated spray decreases rapidly as the GLR increases. For GLR values above a certain threshold, the SMD reaches a constant value that is independent of the GLR. Transfer functions are measured in this second regime for swirling air flows characterized by a swirl number S = 0.92 that is determined by laser Doppler anemometry. Transfer functions defined as the normalized ratio of OH* or CH* flame chemiluminescence intensity fluctuations divided by the velocity oscillation level measured by laser Doppler velocimetry at the burner outlet are determined as a function of the forcing frequency for a small perturbation level. The response of sooty and non sooty flames at globally lean conditions are examined. Using a set of steady experiments, it is shown that the OH* signal may safely be used to confidently estimate low frequency heat release rate disturbances for both types of flames, but the CH* signal cannot be used in the sooty flame cases. The measured transfer functions of non-sooty spray flames feature many similarities with the transfer function of perfectly premixed swirling flames indicating that their dynamics is also controlled by interference mechanisms that need to be elucidated.

Investigation on the Effects of Various Swirl Generators on Heat Transfer and Fluid Flow in Decaying Swirling Flows

2010 ◽  
Vol 224 (10) ◽  
pp. 2181-2197
Author(s):  
M Ahmadvand ◽  
A F Najafi ◽  
S Shahidinejad
Keyword(s):  
Heat Transfer ◽  
Swirling Flow ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Mean Flow ◽  
Inlet Conditions ◽  
The Individual ◽  
Comparison Of The Results

Influences of three typical vortex generators on flow pattern and ensuing heat transfer augmentation were investigated and compared at similar Re and swirl numbers inlet conditions. Studied swirlers such as propeller swirlers, jet-type swirlers, and rotating honeycombs were installed at the pipe inlet. Reynolds number ranges from 10000 to 30000. Swirlers were set on the swirl numbers 1.4, 0.89, and 0.52, which were obtained by propellers. This study has been carried out under uniform heat flux condition and air was employed as the working fluid. The obtained results provide the individual effects of each swirler configuration on mean flow and turbulence distribution as well as on enhancement of heat transfer. Considering S=1.4, jet-type swirlers pointed 133 per cent Nu enhancement compared to axial flow, whereas propellers and rotating honeycombs approached 105 per cent and 79 per cent, respectively. For S=0.89, relative treatment has been changed and propellers with 70 per cent Nu augmentation demonstrated tip-top performance behind of which other swirlers lined. By decreasing the swirl number, approximately closer heat performances were represented from all swirler configurations. Comparison of the results of various swirlers exhibited that Re and swirl numbers are not generally sufficient to determine the swirling flow characteristics and each swirler confirms an individual flow quality.

Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor

2011 ◽  
Author(s):  
Dipanjay Dewanji ◽  
Arvind G. Rao ◽  
Mathieu Pourquie ◽  
Jos P. van Buijtenen
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Numerical Study ◽  
Reverse Flow ◽  
Direct Injection ◽  
Flow Characteristics ◽  
Droplet Breakup ◽  
Reacting Flow ◽  
Lean Direct Injection ◽  
Wide Range

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.

PIV Measurements of Combustor Turbulence Fields

2007 ◽  
Author(s):  
Adrian Spencer ◽  
David Hollis ◽  
Jon Carrotte
Keyword(s):  
Flow Field ◽  
Jet Impingement ◽  
Structure Identification ◽  
Fuel Injector ◽  
Reynolds Stresses ◽  
Isothermal Model ◽  
Validation Data ◽  
Complete Mapping ◽  
Wide Range ◽  
Filtering Effect

An experimental study has been conducted on a full-scale, three-sector, isothermal model of a gas turbine combustor. PIV has been used as the main instrumentation technique and this has been validated against LDA and hot-wire velocity measurements of the same geometry. These data combine to provide high quality boundary condition and validation data for CFD predictions. Substantial care has been taken in assuring the quality of the PIV data. In high turbulence intensity flow fields, low pass spatial filtering can artificially reduce the Reynolds stresses calculated from the PIV measured velocities. The level of this filtering depends upon the ratio of the integral lengthscales in the flow field to the size of the measurement volume of the PIV interrogation cell. Within the highly turbulent flow field of a combustor there exist a very wide range of turbulent length scales. Consideration should therefore be given to any measurements taken in a combustor, hot or cold, to take account of this sub-grid filtering effect. A method is described to overcome this problem and it is demonstrated to be successful by comparing with LDA and PIV data (at increased magnification) that does not suffer this problem. Sparse LDA and HWA data for the combustor is thus complemented by more dense planar PIV data to allow a more complete mapping of the velocity field. This has allowed better understanding of the processes occurring in the combustor such as the jet impingement process and the fuel injector swirler flow interaction with the primary jets. In addition detailed information on turbulence statistics, integral lengthscales, spatial correlation and energetic structure identification is available.

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