Turbulence-Chemistry Interactions in Spray Combustion

2002 ◽  
Author(s):  
Vaidyanathan Sankaran ◽  
Suresh Menon
Keyword(s):  
Heat Release ◽  
Recirculation Zone ◽  
Vortex Breakdown ◽  
Separated Flow ◽  
Spray Combustion ◽  
Mixing Efficiency ◽  
Eddy Simulation ◽  
Swirl Intensity ◽  
Air Mixing ◽  
Combustion Processes

A prediction methodology based on Large-Eddy Simulation (LES) has been used to study turbulence-chemistry interactions in spray combustion. The unsteady interactions between spray dispersion and vaporization, fuel-air mixing and heat release has been investigated using a Stochastic Separated Flow model for spray within the LES formulation. The effects of swirl intensity and heat release are investigated here. Results show that the central toroidal recirculation zone (CTRZ), which is a manifestation of the vortex breakdown process, occurs only under high swirl conditions. Under non-reacting condition, droplets tend to concentrate in regions of low vorticity and increase in swirl increases the dispersion of the droplets. Mixing efficiency is enhanced and the size of the corner recirculation zone is decreased with increase in swirl. Increase in swirl also enhances the combustion processes for cases with heat release.

Spray Combustion Characteristics of Single/Multi-Component Surrogate Fuel for Aviation Kerosene

2022 ◽  
Author(s):  
Wenjin Qin ◽  
Dengbiao Lu ◽  
Lihui Xu
Keyword(s):  
Soot Formation ◽  
Mean Field ◽  
Combustion Characteristics ◽  
Spray Combustion ◽  
Aviation Kerosene ◽  
Eddy Simulation ◽  
Air Mixing ◽  
Flow Field Characteristics ◽  
Lift Off ◽  
Surrogate Fuel

Abstract In this research, n-dodecane and JW are selected as single and multi-component surrogate fuel of aviation kerosene to study the Jet-A spray combustion characteristics. The spray combustion phenomena are simulated using large eddy simulation coupled with detailed chemical reaction mechanism. Proper orthogonal decomposition method is applied to analyze the flow field characteristics, and the instantaneous velocity field are decomposed into four parts, namely the mean field, coherent field, transition field and turbulent field, respectively. The four subfields have their own characteristics. In terms of different fuels, JW has a higher intensity of coherent structures and local vortices than n-dodecane, which promotes the fuel-air mixing and improves the combustion characteristics, and the soot formation is significantly reduced. In addition, with the increase of initial temperature, the combustion is more intense, the ignition delay time is advanced, the flame lift-off length is reduced, and soot formation is increased accordingly.

Large-eddy simulation of separated flow over a swept wing with approximate near-wall modelling

2007 ◽  
Vol 111 (1125) ◽  
pp. 689-697 ◽  
Author(s):  
N. Li ◽  
M. A. Leschziner
Keyword(s):  
Vortex Breakdown ◽  
Separated Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Wall Layer ◽  
Swept Wing ◽  
Validation Data ◽  
Eddy Simulation ◽  
Eddy Viscosity Model ◽  
Near Wall

Abstract The paper investigates, by means of a simulation methodology, the flow separating from a 40 degrees backward-swept wing at 9 degrees incidence and Reynolds number of 210,000, based on the wing-root chord length. The Simulation corresponds to LDA, PIV and suction-side-topology measurements for the same geometry, conducted by other investigators specifically to provide validation data. The finest block-structured mesh contains 23·6 million nodes and is organised in 256 blocks to maximise mesh quality and facilitate parallel solution on multi-processor machines. The near-wall layer is resolved, to a thickness of about y + = 20, by means of parabolised URANS equations that include an algebraic eddy-viscosity model and from which the wall-shear stress is extracted to provide an unsteady boundary condition for the simulation. The numerical solution is in good agreement with the experimental behaviour over the 50-70% inboard portion of the span, but the simulation fails to resolve some complex features close to the wing tip, due to a premature leading-edge vortex breakdown and loss in vortex coherence. The comparisons and their discussion provide useful insight into various physical characteristics of this complex separated wing flow.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

Large-Eddy Simulation and Experimental Observation of Combustion-Induced Vortex Breakdown

2010 ◽  
Vol 182 (4-6) ◽  
pp. 505-516 ◽  
Author(s):  
E. Tangermann ◽  
M. Pfitzner ◽  
M. Konle ◽  
T. Sattelmayer
Keyword(s):  
Large Eddy Simulation ◽  
Experimental Observation ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Large Eddy

Velocity Field Response of a Forced Swirl Stabilized Premixed Flame

2017 ◽  
Author(s):  
Kiran Manoharan ◽  
Travis Smith ◽  
Benjamin Emerson ◽  
Christopher M. Douglas ◽  
Tim Lieuwen ◽  
...  
Keyword(s):  
Heat Release ◽  
Shear Layer ◽  
Recirculation Zone ◽  
Stokes Equations ◽  
Quantitative Agreement ◽  
Forced Response ◽  
Response Analysis ◽  
Annular Jet ◽  
Experimental Response ◽  
Prediction Approach

This study is motivated by the necessity to develop a low order prediction approach for unsteady heat release response characteristics in lean premixed gas turbine combustors. This in turn requires an accurate description of the coherent hydrodynamic oscillations induced in the combustor flow by acoustic forcing. Time resolved velocity and flame position fields are obtained using sPIV and OH-PLIF measurements on a single nozzle, swirl-stabilized, premixed, methane-air flame in a model “unwrapped” annular combustor rig. A natural acoustic oscillation in the rig at 115 Hz results in a coherent flow oscillation that is concentrated primarily within the shear layer between the annular jet flow and the central recirculation zone. A linear stability analysis performed about time averaged base flow fields shows that the flow does not have any self-excited hydrodynamic modes. We then compare predictions from a forced response analysis at a forcing frequency of 115 Hz, based on the linearized Navier-Stokes equations for this coherent response. Good qualitative agreement between linear forced response analysis predictions and experimental response results, is seen for the spatial variation of velocity oscillation amplitude fields, away from the burner centerline. Further, good quantitative agreement between predictions and the experimental response is seen for the phase speed of velocity oscillations along the shear layer between the annular jet and the central recirculation zone. This phase velocity is an important flow field characteristic that has a significant impact on the heat release response that results from these coherent velocity oscillations. Present methods for forced response analysis assume uniform forcing amplitude along the radial direction at the forcing location, as well as, open flows along the streamwise direction. Both these assumptions are not strictly true for the present burner which has a center body on its axis. This maybe the reason for somewhat poor qualitative and quantitative agreement between experiments and predictions at the centerline.

Zonal Detached-Eddy Simulation of Separated Flow Around a Finite-Span Wing

AIAA Journal ◽  
2015 ◽  
Vol 53 (11) ◽  
pp. 3157-3166 ◽  
Author(s):  
F. Richez ◽  
A. Le Pape ◽  
M. Costes
Keyword(s):  
Separated Flow ◽  
Detached Eddy Simulation ◽  
Finite Span ◽  
Eddy Simulation
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