scholarly journals Effect of Modulation of the Inlet Velocity and Equivalence Ratio Gradients on the Stabilization of Stratified Axisymmetric Bluff-Body Flames

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
G. Paterakis ◽  
P. Koutmos
Keyword(s):  
Bluff Body ◽  
Recirculation Region ◽  
Propane Combustion ◽  
Inlet Velocity ◽  
Transverse Acoustic ◽  
Large Eddy ◽  
Gradient Measurements ◽  
Inlet Conditions ◽  
Acoustic Modulation ◽  
The Impact

An investigation of ultralean stratified, disk stabilized, propane flames operated with acoustic modulation of the inlet velocity and fuel-air mixture profiles is presented. Transverse acoustic forcing was applied to the air, upstream of a double-cavity premixer section, formed along three concentric disks, which fueled the stabilization region with a radial mixture gradient. Measurements and supporting Large Eddy Simulations with a nine-step mechanism for propane combustion were performed to evaluate variations in the ultralean flame characteristics under forced and unforced conditions. The effects of forcing on the heat release profiles and on the interaction of the toroidal flame with the recirculation region are examined and discussed. The impact of the acoustic excitation of inlet conditions on the local extinction behavior is, also, assessed by monitoring a local stability criterion and by analyzing phase-resolved chemiluminescence images.

Advanced Statistical Analysis Estimating the Heat Load Issued by Hot Streaks and Turbulence on a High-Pressure Vane in the Context of Adiabatic Large Eddy Simulations

2017 ◽  
Author(s):  
Martin Thomas ◽  
Florent Duchaine ◽  
Laurent Gicquel ◽  
Charlie Koupper
Keyword(s):  
High Pressure ◽  
Large Scale ◽  
Guide Vane ◽  
Large Eddy Simulations ◽  
High Pressure Turbine ◽  
Substantial Impact ◽  
Lean Combustion ◽  
Large Eddy ◽  
Inlet Conditions ◽  
The Impact

The next generation of lean combustion engines promises to further decrease environmental impact and cost of air traffic. Compared to the currently employed Rich Quench Lean (RQL) concept, the flow field at the exit of a lean combustion chamber is characterized by stronger variations of velocity as well as temperature and higher levels of turbulence. These specific features may have a substantial impact on the aerothermal performance of the high-pressure turbine and thereby on the efficiency of the entire engine. Indeed, high levels of turbulence in the Nozzle Guide Vane (NGV) passages locally impact the heat flux and result in globally over dimensioned cooling systems of the NGV. In this study, Large Eddy Simulations (LES) are performed on an engine representative lean combustion simulator geometry to investigate the evolution of turbulence and the migration of hot streaks through the high-pressure turbine. To investigate the impact of non-uniform stator inlet conditions on the estimated thermal stress on the NGVs, adiabatic LES predictions of the lean combustor NGV FACTOR configuration are analyzed through the use of high statistical moments of temperature and two point statistics for the assessment of turbulent quantities. Relations between temperature statistical features and turbulence are evidenced on planes through the NGV passage pointing to the role of mixing and large scale features along with marked wall temperatures that locally can largely differ from obtained mean values.

Large eddy simulations of a transcritical round jet submitted to transverse acoustic modulation

2016 ◽  
Vol 28 (5) ◽  
pp. 055106 ◽  
Author(s):  
M. Gonzalez-Flesca ◽  
T. Schmitt ◽  
S. Ducruix ◽  
S. Candel
Keyword(s):  
Large Eddy Simulations ◽  
Round Jet ◽  
Transverse Acoustic ◽  
Large Eddy ◽  
Acoustic Modulation

Numerical simulation of the 3D unsteady turbulent flow in a combustion chamber

2011 ◽  
Vol 1 (2) ◽  
Author(s):  
Adrian Stuparu ◽  
Sorin Holotescu
Keyword(s):  
Numerical Simulation ◽  
Combustion Chamber ◽  
Gas Flow ◽  
Bluff Body ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Recirculation Region ◽  
Eddy Simulation ◽  
Large Eddy ◽  
3D Unsteady Flow

AbstractThe influence of turbulence models on the 3D unsteady flow in a combustion chamber with a central bluff body is analyzed. Three different turbulence models are used (realizable k-ε, Reynolds Stress Model and Large Eddy Simulation) and a comparison is made on the evolution of the velocity field over time. The numerical simulation of the gas flow in the combustion chamber was performed using FLUENT 6.3 software and the computational geometry, consisting of a structured mesh with 810,000 cells, was built using the pre-processor GAMBIT 2.4. The extent of the recirculation region behind the bluff body was determined for each turbulence model.

scholarly journals Nonlinear Hydrodynamics of a Bluff-Body Stabilized Turbulent Premixed Flame

2016 ◽  
Author(s):  
C. Y. Lee ◽  
R. S. Cant
Keyword(s):  
Limit Cycle ◽  
Bluff Body ◽  
Flame Structure ◽  
Control Flow ◽  
Recirculation Region ◽  
Small Scale ◽  
Nonlinear Behaviour ◽  
Inlet Velocity ◽  
Hydrodynamic Behaviour ◽  
Turbulent Premixed

Bluff-body stabilized turbulent premixed flames can experience hydrodynamic instability caused by the interaction of the flame with small-scale vortices in the separated shear layer around the recirculation region, as well as with the large-scale coherent structures in the far-wake. A globally hydrodynamically unstable system, for example one which involves vortex shedding, can exhibit limit-cycle behaviour due to the coupling between pressure oscillation and velocity fluctuations. In this work, the hydrodynamic behaviour of a bluff-body stabilized turbulent premixed propane/air flame in a model jet-engine afterburner is investigated using Computational Fluid Dynamics (CFD). A URANS approach was found to be appropriate for the range of frequencies considered in this study. Combustion is modelled using a modified flame surface density (FSD) approach. The observed self-excited hydrodynamic oscillations are analyzed using a nonlinear dynamical framework which is capable of capturing elaborate nonlinear behaviour including quasiperiodicity and chaos. The results from the CFD are first validated using available experimental data. The velocity at the inlet is gradually increased from 14 m/s to 33 m/s and the global flame structure is observed. With increasing inlet velocity, the flame first transitions from steady state to an oscillating state with a symmetrical flame structure, and eventually to an asymmetrical flame structure at higher velocities. The flame is essentially steady in the lower range of velocities considered before transitioning to a limit cycle oscillation after a critical velocity is exceeded. A doubling in the frequency of the hydrodynamic oscillation is also observed at intermediate values of inlet velocity. This investigation demonstrates that turbulent premixed reacting flows can exhibit strong hydrodynamic oscillation. An understanding of such behaviour can assist in developing methods to control flow instabilities and therefore help in suppressing thermoacoustic oscillation.

scholarly journals Modelling of a Bluff-Body Stabilised Premixed Flames Close to Blow-Off

Computation ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 43
Author(s):  
Shokri Amzin ◽  
Mohd Fairus Mohd Yasin
Keyword(s):  
Bluff Body ◽  
Fluid Dynamic ◽  
Premixed Flames ◽  
Pollutant Emissions ◽  
Moment Closure ◽  
Recirculation Region ◽  
Scalar Dissipation ◽  
Average Error ◽  
Conditional Moment ◽  
Lean Premixed

As emission legislation becomes more stringent, the modelling of turbulent lean premixed combustion is becoming an essential tool for designing efficient and environmentally friendly combustion systems. However, to predict emissions, reliable predictive models are required. Among the promising methods capable of predicting pollutant emissions with a long chemical time scale, such as nitrogen oxides (NOx), is conditional moment closure (CMC). However, the practical application of this method to turbulent premixed flames depends on the precision of the conditional scalar dissipation rate,. In this study, an alternative closure for this term is implemented in the RANS-CMC method. The method is validated against the velocity, temperature, and gas composition measurements of lean premixed flames close to blow-off, within the limit of computational fluid dynamic (CFD) capability. Acceptable agreement is achieved between the predicted and measured values near the burner, with an average error of 15%. The model reproduces the flame characteristics; some discrepancies are found within the recirculation region due to significant turbulence intensity.

Prediction of liquid-liquid flow in an SMX static mixer using large eddy simulations

2010 ◽  
Vol 64 (2) ◽  
Author(s):  
Paulina Pianko-Oprych ◽  
Zdzisław Jaworski
Keyword(s):  
Centrifugal Force ◽  
Liquid Flow ◽  
Concentration Distribution ◽  
Large Eddy Simulations ◽  
Dispersed Phase ◽  
Static Mixer ◽  
Phase Concentration ◽  
Large Eddy ◽  
Smx Static Mixer ◽  
The Impact

AbstractThe main purpose of the paper is to apply the large eddy simulations (LES) technique and to verify its use as a predicting tool for turbulent liquid-liquid flow in an SMX static mixer. LES modeling was carried out using the Smagorinsky-Lilly model of the turbulent subgrid viscosity for the Reynolds number of 5000 and 10000. The continuous phase was water and the dispersed phase was silicon oil. The investigation covers the effects of the density ratio between the phases. Three different cases of liquid densities were considered. The dispersed phase concentration distribution in the mixer cross-sections was compared with the corresponding time averaged results obtained formerly for the same configuration in a steady-state simulation using the standard RANS approach with the k-ɛ model. The dependency of the standard deviation of the dispersed phase concentration on the distance from the mixer inlet and the impact of the centrifugal force on the phase concentration distribution were investigated. The presented results for the SMX static mixer confirm conclusions of previous studies by Jaworski et al. (2006) obtained for a Kenics static mixer and show less a pronounced influence of the centrifugal force on the phase concentration distribution of the LES results in comparison to the RANS case.

Characteristics of Flame Bases for V-Gutters Stabilized Premixed Flames

2013 ◽  
Author(s):  
Fan Gong ◽  
Yong Huang
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Heat Conducting ◽  
Inlet Velocity ◽  
The Impact

The objective of this work is to investigate the flame stabilization mechanism and the impact of the operating conditions on the characteristics of the steady, lean premixed flames. It’s well known that the flame base is very important to the existence of a flame, such as the flame after a V-gutter, which is typically used in ramjet and turbojet or turbofan afterburners and laboratory experiments. We performed two-dimensional simulations of turbulent premixed flames anchored downstream of the heat-conducting V-gutters in a confined passage for kerosene-air combustion. The flame bases are symmetrically located in the shear layers of the recirculation zone immediately after the V-gutter’s trailing edge. The effects of equivalence ratio of inlet mixture, inlet temperature, V-gutter’s thermal conductivity and inlet velocity on the flame base movements are investigated. When the equivalence ratio is raised, the flame base moves upstream slightly and the temperature gradient dT/dx near the flame base increases, so the flame base is strengthened. When the inlet temperature is raised, the flame base moves upstream very slightly, and near the flame base dT/dx increases and dT/dy decreases, so the flame base is strengthened. As the V-gutter’s thermal conductivity increases, the flame base moves downstream, and the temperature gradient dT/dx near the flame base decreases, so the flame base is weakened. When the inlet velocity is raised, the flame base moves upstream, and the convection heat loss with inlet mixture increases, so the flame base is weakened.

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