Vortex Breakdown in Swirling Fuel Injector Flows

2007 ◽  
Author(s):  
Kris Midgley ◽  
Adrian Spencer ◽  
James J. McGuirk
Keyword(s):  
Vortex Breakdown ◽  
Near Field ◽  
Aerodynamic Characteristics ◽  
Relative Strength ◽  
Turbulence Energy ◽  
Fuel Injector ◽  
Swirl Number ◽  
Helical Vortices ◽  
Helical Vortex ◽  
Air Mixing

It is well known that the process of vortex breakdown plays an important role in establishing the near-field aerodynamic characteristics of fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms, which have been shown in previous papers to include both a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. The unsteady dynamics of these particular features can play an important role in combustion induced oscillations. The present paper reports an experimental investigation, using PIV and hot-wire-anemometry, to document variations in the relative strength of PVC and helical vortex patterns as the configuration of a generic fuel injector is altered. Examples of geometric changes which have been investigated include: • The combination of an annular swirl stream with and without a central jet; • variation in geometric details of the swirler passage, e.g. alteration in the swirler entry slots to change swirl number, and variations in the area ratio of the swirler passage. The results show that these geometric variations can influence: • the axial location of the origin of the helical vortices (from inside to outside the fuel injector); • the strength of the PVC. For example, in a configuration with no central jet (swirl number S = 0.72) the helical vortex pattern was much less coherent, but the PVC was much stronger than when a central jet was present. These changes modify the magnitude of the turbulence energy in the fuel injector near field dramatically, and hence have an important influence on fuel air mixing patterns.

Vortex Breakdown in Swirling Fuel Injector Flows

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Adrian Spencer ◽  
James J. McGuirk ◽  
Kris Midgley
Keyword(s):  
Vortex Breakdown ◽  
Near Field ◽  
Aerodynamic Characteristics ◽  
Relative Strength ◽  
Turbulence Energy ◽  
Fuel Injector ◽  
Swirl Number ◽  
Helical Vortices ◽  
Helical Vortex ◽  
Air Mixing

It is well known that the process of vortex breakdown plays an important role in establishing the near-field aerodynamic characteristics of fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms, which have been shown in previous papers to include both a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. The unsteady dynamics of these particular features can play an important role in combustion induced oscillations. The present paper reports an experimental investigation, using particle image velocimetry (PIV) and hot-wire anemometry, to document variations in the relative strength of PVC and helical vortex patterns as the configuration of a generic fuel injector is altered. Examples of geometric changes that have been investigated include: the combination of an annular swirl stream with and without a central jet; variation in geometric details of the swirler passage, e.g., alteration in the swirler entry slots to change swirl number, and variations in the area ratio of the swirler passage. The results show that these geometric variations can influence: the axial location of the origin of the helical vortices (from inside to outside the fuel injector), and the strength of the PVC. For example, in a configuration with no central jet (swirl number S=0.72), the helical vortex pattern was much less coherent, but the PVC was much stronger than when a central jet was present. These changes modify the magnitude of the turbulence energy in the fuel injector near field dramatically, and hence have an important influence on fuel air mixing patterns.

An Analysis of Unstable Flow Dynamics and Flashback Mechanism Inside a Swirl-Stabilised Lean Burn Combustor

2010 ◽  
Author(s):  
Moresh J. Wankhede ◽  
Neil W. Bressloff ◽  
Andy J. Keane ◽  
Luca Caracciolo ◽  
Marco Zedda
Keyword(s):  
Flame Propagation ◽  
Vortex Breakdown ◽  
Near Field ◽  
Weighted Average ◽  
Fuel Injector ◽  
Unstable Flow ◽  
Time Step ◽  
Lean Burn ◽  
Air Blast ◽  
Injector System

A modern lean burn combustor for propulsion application using a multi-swirler fuel injector system is studied under partially premixed combustion conditions. Combustion induced vortex breakdown (CIVB) plays an important role in establishing the near-field aerodynamic characteristics of lean burn fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms mainly consisting of a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. In the present study a numerical investigation is carried out with an unsteady Reynolds-averaged Navier Stokes (URANS) solver to capture the evolution of the PVC in the vicinity of the air blast atomizer of the injector and the helical vortex patterns inside the combustor. PVC suppression is captured causing upstream flame propagation and a sudden rise in the temperature near the injector end. The existence of hot-spots is reported near the injector end which can increase NOx production and also cause possible damage to the injector assembly itself. The unsteady dynamics of the PVC, which significantly influences fuel efficiency and emissions, are analyzed for a relatively long period of real time. The variation of velocity along the axis of the combustor confirming upstream flame propagation in to the injector is plotted. Mass weighted average temperatures across different planes in the combustor are monitored as target functions. The influence of different time-step sizes on the prediction of the temperature across these different planes is also presented. For this lean burn combustor using a complex multi-swirler fuel injector system, the results demonstrate the formation of a startup PVC in the vicinity of the air blast atomizer of the injector, its unstable mode of excitation, sustainment and suppression due to CIVB over a period of time and its strong influence on injector near-field aero-thermodynamics.

Modeling of Gas Turbine Fuel Nozzle Spray

1997 ◽  
Vol 119 (1) ◽  
pp. 34-44 ◽  
Author(s):  
N. K. Rizk ◽  
J. S. Chin ◽  
M. K. Razdan
Keyword(s):  
Gas Turbine ◽  
Fuel Injection ◽  
Near Field ◽  
Continuous Phase ◽  
Liquid Sheet ◽  
Vapor Concentration ◽  
Fuel Vapor ◽  
Fuel Injector ◽  
Gas Temperature ◽  
Sheet Breakup

Satisfactory performance of the gas turbine combustor relies on the careful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel injection modeling that involves various atomization processes. A two-dimensional fuel injection model has been formulated to simulate the airflow within and downstream of the atomizer and address the formation and breakup of the liquid sheet formed at the atomizer exit. The sheet breakup under the effects of airblast, fuel pressure, or the combined atomization mode of the airassist type is considered in the calculation. The model accounts for secondary breakup of drops and the stochastic Lagrangian treatment of spray. The calculation of spray evaporation addresses both droplet heat-up and steady-state mechanisms, and fuel vapor concentration is based on the partial pressure concept. An enhanced evaporation model has been developed that accounts for multicomponent, finite mass diffusivity and conductivity effects, and addresses near-critical evaporation. The presents investigation involved predictions of flow and spray characteristics of two distinctively different fuel atomizers under both nonreacting and reacting conditions. The predictions of the continuous phase velocity components and the spray mean drop sizes agree well with the detailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formation and breakup at the atomizer exit and the initial drop sizes formed in the atomizer near field region where measurements are difficult to obtain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperature profiles. The results also provided local concentrations of unburned hydrocarbon (UHC) and carbon monoxide (CO) in atomizer flowfield, information that could support the effort to reduce emission levels of gas turbine combustors.

Topological Flow Structures of Annular Swirling Jets

2001 ◽  
Vol 17 (3) ◽  
pp. 131-138
Author(s):  
Feng Chin Tsai ◽  
Rong Fung Huang
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Single Bubble ◽  
Flow Structures ◽  
Complex Flow ◽  
Swirl Number ◽  
Recirculation Bubble ◽  
Annular Jet ◽  
Ring Mode ◽  
Dual Ring

AbstractThe effects of blockage and swirl on the macro flow structures of the annular jet past a circular disc are experimentally studied through the time-averaged streamline patterns. In the blockage-effect regime, the flows present multiple modes, single bubble, dual rings, vortex breakdown, and triple rings, in different regimes of blockage ratio and swirl number. The topological models of the flow structures are proposed and discussed according to the measured flow fields to manifest the complex flow structures. The single bubble is a closed recirculation bubble with a stagnation point on the central axis. The dual-ring flow is an open-top recirculsation zone, in which a pair of counter-rotating vortex rings exists in the near wake. The fluids in the dual rings are expelled downstream through a central jet-like swirling flow. A vortex breakdown may occur in the central jet-like swirling flow if the exit swirl number exceeds critical values. When the vortex breakdown interacts with the dual rings, a complex triple-ring flow structure forms. Axial distributions of the local swirl number are presented and discussed. The local swirl number increases with the increase of the exit swirl number and attains the maximum in the dual-ring mode. At large exit swirl numbers where the vortex breakdown occurs, the local swirl number decreases drastically to a low value.

scholarly journals Characterization of a Novel Porous Injector for Multi-Lean Direct Injection (M-LDI) Combustor

2017 ◽  
Author(s):  
Jianing Li ◽  
Umesh Bhayaraju ◽  
San-Mou Jeng
Keyword(s):  
Air Temperature ◽  
Mass Fraction ◽  
Direct Injection ◽  
Flame Temperature ◽  
Gaseous Fuel ◽  
Nox Emissions ◽  
Fuel Injector ◽  
Porous Tube ◽  
Lean Direct Injection ◽  
Air Mixing

A generic novel injector was designed for multi-Lean Direct Injection (M-LDI) combustors. One of the drawbacks of the conventional pressure swirl and prefilming type airblast atomizers is the difficulty of obtaining a uniform symmetric spray under all operating conditions. Micro-channels are needed inside the injector for uniformly distributing the fuel. The problem of non-uniformity is magnified in smaller sized injectors. The non-uniform liquid sheet causes local fuel rich/lean zones leading to higher NOx emissions. To overcome these problems, a novel fuel injector was designed to improve the fuel delivery to the injector by using a porous stainless steel material with 30 μm porosity. The porous tube also acts as a prefilming surface. Liquid and gaseous fuels can be injected through the injector. In the present study, gaseous fuel was injected to investigate injector fuel-air mixing performance. The gaseous fuel was injected through a porous tube between two radial-radial swirling air streams to facilitate fuel-air mixing. The advantage of this injector is that it increases the contact surface area between the fuel-air at the fuel injection point. The increased contact area enhances fuel-air mixing. Fuel-air mixing and combustion studies were carried out for both gaseous and liquid fuel. Flame visualization, and emissions measurements were carried out inside the exit of the combustor. The measurements were carried out at atmospheric conditions under fuel lean conditions. Natural gas was used as a fuel in these experiments. Fuel-air mixing studies were carried out at different equivalence ratios with and without confinement. The mass fraction distributions were measured at different downstream locations from the injector exit. Flame characterization was carried out by chemiluminescence at different equivalence ratios and inlet air temperatures. Symmetry of the flame, flame length and heat release distribution were analyzed from the flame images. The effects of inlet air temperature and combustion flame temperature on emissions was studied. Emissions were corrected to 15% O2 concentration. NOx emissions increase with inlet air temperature and flame temperature. Effect of flame temperature on NOx concentration is more significant than effect of inlet air temperature. Fuel-air mixing profile was used to obtain mass fraction Probability Density Function (pdf). The pdfs were used for simulations in Chemkin Pro. The measured emissions concentrations at the exit of the injector was compared with simulations. In Chemkin model, a network model with several PSRs (perfectly stirred reactor) were utilized, followed by a mixer and a PFR (plug flow reactor). The comparison between the simulations and the experimental results was investigated.

Aerodynamic characteristics of delta wing–body combinations at high angles of attack

1994 ◽  
Vol 98 (975) ◽  
pp. 159-170 ◽  
Author(s):  
P. R. Viswanath ◽  
S. R. Patil
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Aerodynamic Characteristics ◽  
Surface Flow ◽  
Flow Visualisation ◽  
Symmetric Flow ◽  
Gradual Process ◽  
Wing Sweep ◽  
The Mean ◽  
High Angles Of Attack

AbstractAn experimental study investigating the aerodynamic characteristics of generic delta wing-body combinations up to high angles of attack was carried out at a subsonic Mach number. Three delta wings having sharp leading edges and sweep angles of 50°, 60° and 70° were tested with two forebody configurations providing a variation of the nose fineness ratio. Measurements made included six-component forces and moments, limited static pressures on the wing lee-side and surface flow visualisation studies. The results showed symmetric flow features up to an incidence of about 25°, beyond which significant asymmetry was evident due to wing vortex breakdown, forebody vortex asymmetry or both. At higher incidence, varying degrees of forebody-wing vortex interaction effects were seen in the mean loads, which depended on the wing sweep and the nose fineness ratio. The vortex breakdown on these wings was found to be a gradual process, as implied by the wing pressures and the mean aerodynamic loads. Effects of forebody vortex asymmetry on the wing-body aerodynamics have also been assessed. Comparison of Datcom estimates with experimental data of longitudinal aerodynamic characteristics on all three wing-body combinations indicated good agreement in the symmetric flow regime.

scholarly journals Velocity measurements in the near field of a diesel fuel injector by ultrafast imagery

2013 ◽  
Vol 54 (2) ◽  
Author(s):  
David Sedarsky ◽  
Saïd Idlahcen ◽  
Claude Rozé ◽  
Jean-Bernard Blaisot
Keyword(s):  
Diesel Fuel ◽  
Near Field ◽  
Fuel Injector ◽  
Velocity Measurements

scholarly journals Multiple helical modes of vortex breakdown

2011 ◽  
Vol 683 ◽  
pp. 430-441 ◽  
Author(s):  
J. N. Sørensen ◽  
I. V. Naumov ◽  
V. L. Okulov
Keyword(s):  
Stability Theory ◽  
Vortex Breakdown ◽  
Cavity Flow ◽  
Driven Cavity ◽  
Aspect Ratios ◽  
Helical Vortex ◽  
Stable Vortex

AbstractExperimental observations of vortex breakdown in a rotating lid-driven cavity are presented. The results show that vortex breakdown for cavities with high aspect ratios is associated with the appearance of stable helical vortex multiplets. By using results from stability theory generalizing Kelvin’s problem on vortex polygon stability, and systematically exploring the cavity flow, we succeeded in identifying two new stable vortex breakdown states consisting of triple and quadruple helical multiplets.

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