Non-reacting Jet Research Articles

Numerical Investigation of the Reactive Impinging Jet Cooling – the role of vortices in heat and mass transfer intensification

While fundamental mechanisms of non-reactive jet impingement have been extensively researched, the reactive jet impingement is yet unexplored although it offers the potential to increase further the heat transfer. The present work fills this knowledge gap via high-fidelity numerical simulation of reactive jet impingement invoking the finite rate one-step chemistry. Endo-/exothermic reactions are found to have very limited influence on time-averaged fluid flow, while they induce substantial modifications in heat transfer characteristics. This influence is manifested as discernible changes in the momentary or instantaneous fluid dynamics. Specifically, the primary vortices are responsible for downwashing cold fluid (mostly N2O4) towards the hot plate, posing low local convective heat transfer. The secondary vortices are responsible for extracting heat from the hot plate via the dissociation reaction N2O4→2NO2, followed by transporting NO2 away from the hot plate and towards the upwashing side of the primary vortex. At the upside of the primary vortex, hot NO2 is cooled by the environment, therefore reforming N2O4 to give out energy. This intense and long-lasting heat absorption and heat release process explains the outstanding performance of reactive jet impingement.

Confinement effect on recirculation structures in isothermal coaxial swirling jet

The present experimental work reports first observations of effect of confinement on recirculation structures in non-reacting coaxial swirling jet in geometric swirl number range of SG= 2.14–2.88. In particular, particle image velocimetry (PIV) has been employed to study the effect of two confinement ratios (CR) viz. 1.82 and 2.73 on two types of recirculation zones (RZ) i.e., pre-breakdown dual rings (PVB) and central toroidal recirculation zone (CTRZ) observed in coaxial swirling jet. It is observed thatCR = 1.82 produces a slight radial expansion in PVB whereas significant compaction and streamwise elongation is observed in CTRZ. The difference in the observation is explained on the basis of modified Rossby number (Rom). The PVB flow state which is characterised byRom > 1 presents significant resistance to wall effect to be felt till the centerline. Contrarily, the CTRZ flow mode characterised byRom < 1allows the wall effect to be felt till the centerline, in turn affecting the RZ entirely. TheCR = 2.73 is shown to offer larger area for the RZ to spread radially outwards. Resultantly, the PVB and CTRZ are shown to significantly widen. Other significant comparisons betweenCR = 1.82 and 2.73 for PVB and CTRZ are elaborated using contour plots of axial and radial strain rates.

Well blowout Flame's thermal radiation prediction under environmental wind based on multi-point heat sources and inverse analysis

This study addresses the inadequacy of traditional multi-point source thermal radiation models in predicting the thermal radiation of gas well blowout fires under windy conditions. Initially, a Computational Fluid Dynamics (CFD) approach for predicting thermal radiation from well blowout jet flames was developed and validated against existing literature. Subsequently, the impact of wind on the thermal radiation of well blowout flames was thoroughly analyzed based on CFD model. Next, a novel predictive model for the center trajectory of well blowout flames under wind conditions was introduced based on CFD numerical simulation results and non-reactive jet trajectory theory. Building upon this, a novel prediction method of well blowout flame's thermal radiation under wind condition was proposed based on weighted multi-point sources model. Finally, the weights within proposed model were refined using an inverse optimization technique, specifically the Conjugate Gradient Global Optimization Algorithm, while also establishing a correlation between the optimal weight and the operating condition parameters of well blowout fires. Results indicated that the average difference between the thermal radiation values computed by the proposed method and those derived from numerical simulations was less than 10%. And the proposed model demonstrates clear superiority, particularly in terms of accuracy and convenience compared with traditional multi-point source model and single point source model. This research offers a practical and effective method for predicting thermal radiation from well blowout flames under wind conditions, which was of great significance for well blowout fire's disposal and rescue.

Method and algorithm for calculating isobaric and non-isobaric three-dimensional turbulent jets of reacting gases

This paper presents a calculation method and algorithm, as well as numerical results of studying chemically reacting turbulent jets based on three-dimensional parabolic systems of Navier-Stokes equations for multicomponent gas mixtures.Continuity equations are used to calculate the mass imbalance when solving with constant pressure, and with variable pressures, with the equations of motion and continuity.Diffusion combustion of a propane-butane mixture flowing from a square-shaped nozzle in a submerged flow of an air oxidizer has been numerically studied. Pressure variability significantly affects the velocity (temperature) profiles in the initial sections of the jet, and when moving away from the nozzle exit, the pressure effect can be considered imperceptible, but the flame length is longer than at constant pressure, but it does not significantly affect the shape of the flame.The saddle-shaped behavior of the longitudinal velocity in the direction of the major axis is numerically obtained for large initial values of the turbulence kinetic energy of the main jet.Given method allows the study of non-reacting and reactive turbulent jets flowing from a rectangular nozzle.

Pressure-based large-eddy simulation of under-expanded hydrogen jets for engine applications

An assessment of Large-Eddy Simulations (LES) of non-reactive under-expanded hydrogen jets by using a pressure-based algorithm is presented. Such jets feature strong compressible discontinuities often considered to be best dealt with by a density-based solver. The crucial contribution of this work is to evaluate the suitability of the pressure-based solver to correctly describe the flow field of gaseous hydrogen jets for engine applications, despite the presence of shock waves in the under-expanded near-orifice region. Inherently, the paper aims at providing guidance on the corresponding numerical aspects to simulate these flows. Hydrogen jets in an argon atmosphere at three different injection pressures are simulated and the results are compared to experiments in literature. Jet tip penetration and cone angle are the main investigated parameters. A good match is found, confirming the solidity of the proposed model. Different LES sub-grid scale models and discretisation schemes are then investigated in order to find the best approach in terms of accuracy and required computational cost. In particular, it is found that the WALE model coupled with a 4th-order cubic scheme for the convective terms yields the most suitable configuration.

On molecular unmixedness between the ejected original and entrained ambient fluids in a turbulent jet

The present study investigates the molecular unmixedness between the injected and entrained fluids in a turbulent jet as well as its dependence on the initial conditions. This unmixedness can be quantified as the parameter of molecular segregation between the ejecting “fuel” fluid (A) and the entrained “oxidizer” fluid (B), defined by α≡cAcB¯/C¯AC¯B (overbar denotes time-averaging). For the first time, an expression of the parameter has been derived for the two-fluid mixing in a heated turbulent nonreactive jet. That is, α=−θ2¯/Θo−Θ¯Θ¯−Θa, where Θo and Θa denote the ejected “warm” and entrained “cold” fluid temperatures, whereas Θ and θ are the instantaneous and fluctuating temperatures of the local fluid mixture. This expression of α is well validated by comparing the measured natural-gas flames from a smooth-contraction nozzle with those from a long-pipe nozzle. Moreover, the jet-nozzle configuration is found to show a strong effect on α. Likewise, the jet density ratio (Rρ) is a highly influential factor: e.g., an increase in Rρ reduces α substantially. In contrast, the effect of the jet-exit Reynolds number is less significant. In the present paper, we try to explain these observations.

Numerical Study of Velocity and Mixture Fraction Fields in a Turbulent Non-Reacting Propane Jet Flow Issuing into Parallel Co-Flowing Air in Isothermal Condition through OpenFOAM

This research employs computational methods to analyze the velocity and mixture fraction distributions of a non-reacting Propane jet flow that is discharged into parallel co-flowing air under iso-thermal conditions. This study includes a comparison between the numerical results and experimental results obtained from the Sandia Laboratory (USA). The objective is to improve the understanding of flow structure and mixing mechanisms in situations where there is no involvement of chemical reactions or heat transfer. In this experiment, the Realizable k-ε eddy viscosity turbulence model with two equations was utilized to simulate turbulent flow on a nearly 2D plane (specifically, a 5-degree partition of the experimental cylinder domain). This was achieved using OpenFOAM open-source software and swak4Foam utility, with the reactingFoam solver being manipulated carefully. The selection of this turbulence model was based on its superior predictive capability for the spreading rate of both planar and round jets, as compared to other variants of the k-ε models. Numerical axial and radial profiles of different parameters were obtained for a mesh that is independent of the grid (mesh B). These profiles were then compared with experimental data to assess the accuracy of the numerical model. The parameters that are being referred to are mean velocities, turbulence kinetic energy, mean mixture fraction, mixture fraction half radius (Lf), and the mass flux diagram. The validity of the assumption that w߰ = v߰ for the determination of turbulence kinetic energy, k, seems to hold true in situations where experimental data is deficient in w߰. The simulations have successfully obtained the mean mixture fraction and its half radius, Lf, which is a measure of the jet’s width. These values were determined from radial profiles taken at specific locations along the X-axis, including x/D = 0, 4, 15, 30, and 50. The accuracy of the mean vertical velocity fields in the X-direction (Umean) is noticeable, despite being less well-captured. The resolution of mean vertical velocity fields in the Y-direction (Vmean) is comparatively lower. The accuracy of turbulence kinetic energy (k) is moderate when it is within the range of Umean and Vmean. The absence of empirical data for absolute pressure (p) is compensated by the provision of numerical pressure contours.

The influence of a plasma actuator embedded in a bluff-body on the stabilization of nonpremixed jet flames

This study is to experimentally investigate the influence of an annular plasma actuator embedded in a bluff body burner on flame stabilization, extending the previous work on non-reacting jets to propane jet diffusion flames. The objective of the actuator is to produce a vortex ring in the vicinity of the jet exit, subsequently to alter the local flow velocity, and thus to achieve flame stabilization. Results show that repetitive flame reattachment may occur with the presence of the induced vortex ring. Flame reattachment frequency and attachment time are analyzed with fast Fourier transform (FFT) and a probability density function (PDF), respectively, and both results suggest that the degree of interaction between the flame and the vortex ring has strong dependence on the imposed flow momentum, characterized by the momentum ratio of the vortex ring to the main jet. A flame describing function (FDF), characterizing the dynamic flame response to the induced flow, exhibits a trough where the vortex ring momentum is comparable to the jet momentum. Given the constant vorticity independent of the jet momentum, a greater degree of interaction between the vortex ring and the fuel jet leads to more repetitive flame reattachment, resulting in more steady heat release.

Pulse picking of a fiber laser enables velocimetry of biomass-laden jets at low and ultra-high repetition rates

The introduction of fibrous aspherical biomasses for the substitution of coal as a sustainable solid fuel causes complex particle-turbulence interactions, which need to be captured using minimally invasive laser-based diagnostics. High-resolution two-phase particle image velocimetry (PIV) of high-velocity biomass-laden turbulent flows require laser inter-pulse times of only a few microseconds, which is usually achieved with separate laser systems for low-speed statistical and time-resolved measurements. In this work, we introduce a novel approach to achieve low-speed dual-pulse and ultra-high-speed time-resolved two-phase PIV using a single laser system. The flexible repetition rate laser output is realized by coupling a continuously pulsing fiber laser to an acousto-optic deflector (AOD) for pulse picking. The selective deflection of two adjacent laser pulses into the measurement volume is presented at a camera repetition rate of 25 Hz and laser repetition rate of 312.5 kHz resulting in an inter-pulse time of 3.2 µs. Temporal limitations of the AOD pulse picking system are evaluated beyond the access time limit for partially overlapping pulse pairs. To demonstrate the feasibility of the diagnostic system, low-speed measurements and additional ultra-high-speed measurements at 200 kHz are performed at high spatial resolutions to resolve individual biomass particles and their surrounding flow field in a non-reacting turbulent round jet. Simultaneous diffuse back-illumination measurements using a pulsed LED for particle size measurements of a high-aspect-ratio biomass (miscanthus) are conducted. The diagnostic system offers the capability of determining the slip velocity field and projected particle size, enabling a direct measurement of the local particle Reynolds number under high-velocity turbulent conditions at low and ultra-high repetition rates.

Effects of jet/flame interaction on deflagration-to-detonation transition by non-reactive gas jet in a methane-oxygen mixture

Jet-in-crossflow (JICF) is a potential and reliable technique that can promote flame acceleration and deflagration-to-detonation transition (DDT). Most of the previous researches utilized combustible mixture or oxygen as the medium of JICF, therefore the detonation enhancement effect may be partly attributed to the chemical properties of the jet, and the purely turbulent effect induced by JICF on DDT has not been fully understood. In our previous work, the non-reactive gas jet affected flame propagation indirectly by separating the injection and ignition in the control sequence. A competing mechanism between the positive combustion-enhancement effect caused by jet-induced turbulence and the negative non-reactive gas-inhibition effect on combustion has not been found, the non-reactive gas jet with high pressure and short duration time was also verified to be beneficial for precursor shock wave formation and flame acceleration. However, no detonation was observed in the work. In this paper, the non-reactive jet interacts with the flame propagation directly by overlapping the working time of the jet and ignitor partly, and the effect of jet parameters including injection pressure and time delay on DDT is investigated systematically. The results show that the flame affected by the non-reactive gas jet with a high-pressure ratio and a short time delay can transit to detonation in a short run-up distance successfully. The schlieren images of the flame evolution process illustrate that the flame interacted by the jet experiences four states: layered flame, wrinkled flame, cellular flamelets, and turbulent flame. Kelvin–Helmholtz (K-H) instability and Rayleigh-Taylor (R-T) instability dominate in the flame distortion. The characteristic timescales of the flow and reaction are computed in the four flame states, turning out that as the flame evolving, the turbulent intensity of the flame is enhanced. Damköhler number (Da) on the flame front eventually converges to [1,2] demonstrates the characteristic timescales of the turbulence and reaction are on the same order, and the turbulence dominates the flame evolution.

Investigation of the effect of turbulence induced by double non-reactive gas jet on the deflagration-to-detonation transition

Jet-in-crossflow (JICF) is proved to be advantageous to accelerate flame propagation and stimulate the deflagration-to-detonation transition (DDT) process in the recent decade. Studies focused on the performance of the jet of combustible mixture or reactive gas on facilitating the DDT process are carried out, and the results show that the combustible JICF can promote the flame transition to detonation efficiently. Although most investigations attribute the ability of the JICF on promoting DDT to the turbulent effect induced by the jet, the combustion-enhancement effect of the jet medium is seldom considered. In our previous work, it is proposed that the non-reactive gas jet in an optimal condition can accelerate flame propagation and promote the precursor shock wave formation. Hence, the performance of the multi-jet of non-reactive gas on facilitating the DDT process is worth investigating. In this paper, three different double jet placement methods are designed: parallel, staggered, and opposite positioned, and their performances on accelerating flame propagation and promoting the DDT process are investigated systematically. The results indicate that the staggered jet can accelerate the flame to detonation within a short run-up distance whereas the parallel jet and the opposite jet can only make the flame accelerate slightly. The schlieren images of flame evolution affected by double jet indicate that the complicated reactivity gradients generate on the flame surface while the flame is disturbed by the double jet. The interaction between the staggered jet and the flame induces local explosions, which results in a prominent increase of the flame area and a large volumetric burning rate. For the opposite jet, its negative effect of combustion-inhibition of the aggregated CO2 overwhelms the positive effect of turbulence-enhancement on the flame acceleration.

Resolvent-based modelling of coherent structures in a turbulent jet flame using a passive flame approach

Motivated by the recent success in finding coherent structures in turbulent flows and describing their noise emission using the Resolvent Analysis (RA), the method is applied to a turbulent jet flame at Re=15,000 and a corresponding non-reacting flow to investigate their axisymmetric dynamics. The RA, which in this study assumes a passive flame and neglects compressibility effects, is based on the governing equations linearized around the temporal mean state. It is validated against Spectral Proper Orthogonal Decomposition (SPOD) obtained from time-resolved snapshots. Both the temporal mean state and the snapshots are obtained by Large Eddy Simulation (LES). The SPOD reveals that an axisymmetric, convective Kelvin–Helmholtz (KH) instability is the dominant hydrodynamic mechanism in the jet flame within a narrow frequency band and incorporates up to 40% of the turbulent kinetic energy. Results show that the RA is capable of reproducing the mode shapes seen in the SPOD. The RA furthermore allows to address the origin of these hydrodynamic structures: While the corresponding KH mode in a non-reacting turbulent jet flow is most sensitive to perturbations in the nozzle boundary layer, the same dominant mode in the turbulent Bunsen flame is most receptive to perturbations in the region between the nozzle edge and the annular pilot burner. The results suggest that the strong density gradients in this region initiate perturbations in the baroclinic torque, which are feeding the KH mode. Finally, a linear stability analysis proves that the high sensitivity of the KH structure is due to resonance with stable linear eigenmodes, which explains its high energy content. By applying the RA to a turbulent reacting flow, this study opens up a new pathway in analyzing the role of hydrodynamic structures in reacting flows.

Modeling of liftoff heights of non-premixed turbulent flames in co-flows having various temperatures and O2 concentrations

Lifted flames in combustion furnaces are diluted with burned gas entrained into the fuel jet. The reduced concentrations of reactants resulting from this dilution increase the liftoff height, while the associated temperature increase decreases the height. The aim of the present study was to develop a premixed model capable of predicting the variation in the liftoff height resulting from entrainment. A triple concentric burner incorporating fuel gas, oxidizer and co-flow gas nozzles was employed to simulate a combustion furnace. Prior to combustion tests, the fraction of the fuel gas in the non-reactive jets forming on the burner was determined, to allow an evaluation of parameters affecting the entrainment rate of the co-flow gas. The flame liftoff height above the burner was found to increase with decreases in the O2 concentration in the co-flow gas and was decreased with increases in temperature. Three premixed models were examined: a conventional premixed model, a DP1 model including only the effect of decreasing reactant concentrations and a DP2 model including the effects of both decreasing concentrations and temperature increases. Validations of these models demonstrated that the conventional model failed to predict variations in the liftoff height at a variety of co-flow gas O2 concentrations and temperatures. The DP1 model also provided insufficient correlations between the bulk velocity and liftoff height, such that the correlation line at a high co-flow gas temperature separated from that at room temperature. In contrast, the DP2 model provided excellent correlations in conjunction with different virtual origin positions.

Microscopic spray measurements of non-reacting alternative jet fuel: Effect of ambient gas temperature

The volatile characteristics of alternative Gas-to-Liquid (GTL) jet fuel and conventional Jet A-1 fuel are significantly different due to their chemical composition variations. This difference can have a strong influence on the atomization performance at elevated ambient gas temperature conditions. Because the atomization process plays a vital role in fuel distribution inside the combustor, which ultimately affects heat release and emission patterns. The objective of the present work is to investigate the effects of ambient gas temperature and nozzle pressure differential on the non-reacting, microscopic spray performance of the alternative jet fuel using a pressure-swirl nozzle, and then, compare these effects to those of Jet A-1 fuel. Specifically, this study investigates the droplet size, velocity and distribution, by employing the Phase Doppler Anemometry technique to measure these parameters at several radial and axial locations downstream of the nozzle exit. The effect of ambient gas temperatures is studied at 300, 350, and 400 K at two nozzle pressure differentials, 300 and 900 kPa, while maintaining a constant ambient gas pressure and fuel temperature. Results show that, in the region investigated, there is a significant difference between the spray performances of GTL and Jet A-1 at elevated operating conditions. The outcomes of this study will add new knowledge to the limited scientific literature on the effect of ambient gas conditions on the local spray parameters of alternative jet fuel.

Numerical Study of Scramjet Combustor with Tandem Dual Cavity for Nonreactive Jets

In the past decades flame out is a major phenomenon that paves way for high fuel consumption in scramjet combustion. For enhancing mixing and flame holding characteristics, different types of cavities are introduced in a scramjet combustion chamber which can hold air for a bit and acts like an atomizer. For increasing combustion efficiency and burnout ratios recirculation is maintained by using cavity and ramp angle techniques. In this paper numerical analysis has been carried out for two dimensional non-reacting flows in the combustor of scramjet engine with tandem dual cavity that creates high turbulent kinetic energy for ensuring combustion instability. This work is an enlightened approach for predicting the flow phenomenon that induces re-circulations after implementing various tandem dual cavities with varying length to diameter ratio and ramp angle. These in turn overcome low mixing rates due to compressibility effects at high convective Mach number.

A Novel One- and Zero-Dimensional Model for Turbulent Jet Ignition

Turbulent jet ignition (TJI) is a promising combustion technology for burning highly diluted air-fuel mixtures. Computationally efficient models to assess the effect of the operating conditions and design parameters on the ignition propensity and timing are of paramount importance for the development of combustion systems employing TJI. To this end, a one-dimensional (1-D) jet model, which is based on the solution of the section integrated mass and momentum conservation equations, is derived in the present study. The model is extended with two additional transport equations for the turbulence intensity and the ignition precursor/tracer, that marks the ignition event. One-dimensional transient flamelet calculations are performed to generate tables for the ignition precursor source term that account for the turbulence and chemistry interaction. Further simplification of the model is carried out to obtain a novel penetration correlation and a computationally inexpensive Lagrangian ignition model. The extended jet model is hierarchically validated using available literature data for non-reactive and reactive jets, as well as experiments conducted in a state-of-the-art optically accessible prechamber. The derived model is able to reproduce both flow-related quantities (velocity and turbulence profiles, jet penetration) and the ignition delay time under different variations. This study also illustrates how numerical simulations in canonical configurations (one-dimensional flamelet) can be used in practical applications of TJI.

Stress-Blended Eddy Simulation/Flamelet Generated Manifold Simulation of Film-Cooled Surface Heat Transfer and Near-Wall Reaction

Abstract Accurate numerical prediction of surface heat transfer in the presence of film cooling within aero-engine sub-components, such as blade effusion holes and combustor liners, has long been a goal of the aero-engine industry. It requires accurate simulation of the turbulent mixing and reaction processes between freestream and the cooling flow. In this study, the stress-blended eddy simulation (SBES) turbulence model is used together with the flamelet generated manifold (FGM) combustion model to calculate the surface heat flux upstream and downstream of an effusion cooling hole. The SBES model employs a blending function to automatically switch between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) based on the local flow features, and thus significantly reduces the computational cost compared to a full LES simulation. All simulations are run using ansys fluent®, a commercial finite-volume computational fluid dynamics (CFD) solver. The test case corresponds to an experimental rig run at Massachusetts Institute of Technology (MIT), which is essentially a flat plate brushed by a uniform freestream of argon with ethylene seeded inside, and is cooled by either a reacting air or a non-reacting nitrogen jet inclined at 35 deg to the freestream. Calculations are performed for both reacting and non-reacting jet cooling cases across a range of jet-to-stream blowing ratios and compared with the experimental data. The effects of mesh resolution are also investigated. Calculations are also performed across a range of Damköhler number (i.e., flow to chemical time ratio) from zero to 30, with unity blowing ratio, and the differences in the maximum surface heat flux magnitude in the reacting and non-reacting cases at a specific location downstream of the hole are investigated. Results from these analyses show good correlation with the experimental heat flux data upstream and downstream of the cooling hole, including the heat flux augmentation due to local reaction. Results from the Damköhler number sweep also show a good match with the experimental data across the range investigated.

Numerical simulation of non-reacting fuel-air coaxial jets by means of a novel high-order method

The present work deals with the development of an original Discontinuous Galerkin (DG) finite element code and its application to compute the non-reactive aerodynamics of multicomponent gaseous mixtures in turbulent regime. Recent developments of the DG approach show great potential in computing high-order accurate solutions on arbitrarily complex grids even in the presence of strong discontinuities and thus the method is well suited for modeling combustion aerodynamics. The study of coaxial jets, with and without swirl, is indeed of paramount importance in assessing burner and combustor performance and the accurate understanding of their fluid dynamic behaviour is an essential prerequisite to subsequently investigate their reactive counterpart. The predictive capabilities of the novel method proposed are verified against several experimental tests taken from three different databases, selected to cover the widest range of coaxial jets operating conditions, and compared with simulations carried out using a commercial code, at most second-order accurate. Notwithstanding the numerical prediction of turbulent gaseous mixture is indeed challenging, it is shown that the DG method exhibits a good accuracy level even on coarse grids and allows to properly resolve the relevant jet structures and characteristic features.

Non-isothermal mixing characteristics in the extreme near-field of turbulent jets in hot crossflow: Effects of jet exit turbulence and velocity profile

The non-reacting and reacting jets-in-crossflow (JICF) are important flow configurations for effective mixing and combustion in practical applications. Many studies in the literature examine the overall mixing characteristics of isothermal, unconfined, non-reacting JICF. This experimental study expands on our recently published work that examined mixing characteristics in the near-field of a non-reacting jet in a hot vitiated crossflow (1500 K) for the jet-to-crossflow density ratio between 3.2 and 7.8 issuing from a round jet with a fully developed turbulent pipe flow exit profile. In this study, effects of the changing jet exit velocity profile to top-hat as well as exit turbulence levels (28% and 40%) with parabolic profiles are examined. Temperature measurements were made using laser Rayleigh scattering. The jet trajectory, centerline concentration decay based on adiabatic mixing assumption, Favre-averaged scalar dissipation, and mixing time scales were compared with the previous study results. Center-plane mixing metrics indicated that top-hat and pipe flow jets behave similarly, with better near-field mixing at lower momentum flux ratios and higher density ratios. The elevated turbulence cases have a higher near-field mixing efficiency with rates that are nearly independent of momentum flux ratios above 9.3 at a constant density ratio. Scalar dissipation analysis showed that the elevated turbulence jets differ from the nominal turbulence top-hat and pipe exit jet cases with a lack of strong peaks and slightly higher upstream crossflow magnitudes. Reducing the density ratio resulted in a decrease in the windward and leeward dissipation region size and magnitude.

Dissipation element analysis of non-premixed jet flames

Abstract