Turbulent Zone Research Articles

AN ALTERNATIVE VIEW OF THE ISRAEL-PALESTINE DISPUTE: THE ESCHATOLOGICAL DIMENSION

<p>This article examines the Israel-Palestine conflict through the lens of eschatology, a religious belief concerning end-of-age expectations, which often incites violent reactions. Despite extensive research on the Israel-Palestine conflict, there is a lack of comprehensive studies exploring the role of eschatology in this context. The Middle East, including Israel and Palestine, is a turbulent war zone with religion significantly fueling extreme hatred and violence. The focus is on the impact of religious traditions, particularly eschatology, which is prone to provoke violent reactions. The study analyzes this through five sections: eschatology prophecy, daily religion, Jerusalem’s role, expansion beyond Jerusalem, and the conveyed message. The article concludes that eschatology significantly influences this conflict, with violent apocalyptic prophecies exacerbating the situation. Resolving this conflict necessitates diverse interpretations of eschatology and apocalyptic prophecies and understanding religion’s role in the conflict.</p>

Horizontal Resolution Sensitivity of the Simple Convection‐Permitting E3SM Atmosphere Model in a Doubly‐Periodic Configuration

AbstractWe develop a doubly periodic version of the Simple Convection‐Permitting E3SM Atmosphere Model (SCREAM) to provide an efficient configuration for this global convection permitting model (GCPM), akin to a single column model often found in conventional general circulation models. The design details are explained, in addition to the extensive case library associated with the doubly periodic SCREAM (DP‐SCREAM) configuration. We demonstrate that doubly periodic cloud resolving models are useful tools to explore the horizontal resolution sensitivity of GCPMs, in addition to replicating biases seen in the global models. Using DP‐SCREAM, we show that SCREAM exhibits behaviors of a scale aware model as it is able to naturally partition between sub‐grid scale (SGS) and resolved vertical transport across the gray zone of turbulence. We show that SCREAM is reasonably scale insensitive when run at resolutions from 1 to 5 km, but can exhibit sensitivity, particularly for the shallow convective regime, when run at resolutions approaching that of large eddy simulations. We conclude that SGS parameterization improvements are likely needed to reduce this scale sensitivity.

Characteristic Analysis of Relationship Between Precipitation and Turbulence in the Troposphere and Lower Stratosphere Over Tropical Western Pacific

AbstractThis study aims to analyze the distribution characteristics of turbulence in the western Pacific tropical region and determine the correlation between turbulence and precipitation. The obtained results show that due to the combined action of large wind shear and thermal convection, the near‐surface layer is conducive to the generation of large‐scale turbulence, and the maximum Thorpe scale can reach more than 600 m. A strong mixing zone of turbulence is generated in 10–16 km, with the monthly average occurrence rate of turbulence being about 40% and the maximum value reaching 50%. There is less turbulence in lower stratosphere due to the rapidly increased atmosphere static stability. All Thorpe scales in stratosphere are less than 100 m. The response of turbulence to precipitation in the upper troposphere is strongly affected by clouds. At the altitude in the clouds, the enhancement of precipitation has a negative relationship with turbulence. The average value of and turbulence layer thickness on rainy days are both smaller than those when the precipitation weakened. At the altitude above the clouds, the enhancement of precipitation has a slight promotion effect on the turbulence, especially for the emergence of large‐scale turbulence. When the precipitation intensifies, the amount of turbulence with greater than 150 m accounts for 6.7% of the total, while the proportion is only 2.6% on less rainy days.

Applications of drag reducers for the pipeline transportation of heavy crude oils: A critical review and future research directions

AbstractThe long‐distance pipeline transportation of heavy crudes demands optimal pumping procedures to abate overhead expenditures in the midstream phase. This can be facilitated by reducing both the oil viscosity and the frictional losses induced by the turbulent flow zone. The dualistic approach of reducing both viscosity and drag requires the optimization of several parameters such as concentrations and types of diluents and additives. This manuscript critically reviews various technologies being undertaken to facilitate the pipeline transportation of heavy crude oils by highlighting the technique of dilution coupled with the addition of drag reducing agents (DRA). DRA such as surfactants, nanoparticles, bio‐additives, polymers, and fibres are blended with the diluted crudes to suppress the proliferation of turbulent eddies which in turn assist in pumping the oil at a higher flow rate under constant pressure conditions. Several investigations have reported that drag reduction is significantly enhanced by varying the molecular structure of the DRA. In addition, an optimum flow rate coupled with a specific surfactant concentration at an ideal temperature can significantly reduce head losses and pumping expenditures. Further research is imperative to study the effect of the polymer structure with respect to the induced shear degradation and dissolution behavior of the crude.

Blending in unbaffled and baffled mechanically agitated vessels – Effect of Reynolds number and liquid height

The standard vessel for mixing in the process industry is a baffled tank. This design is very common especially for low viscosity fluids. Nonetheless, unbaffled vessels are found in industry and the laboratory. The reasons given for using unbaffled vessels are primarily concerns around cleaning the vessel between batches and the possibility of stagnation zones in high viscosity fluids particularly when properties change over the processing time. In this paper we will examine the effect of baffles on the blend time using one vessel: with and without baffles. The blend time was measured using the iodine color change method using a range of viscosities and Reynolds Numbers. The depth of the vortex was also measured. The same axial flow-down pumping impeller is used. In this work we observed that the flow patterns are dramatically different between unbaffled and baffled tanks. At high Reynolds Numbers with the baffled configuration, we see the familiar turbulent diffusion throughout the vessel. Without the baffles the fluid segregates into two zones: a swirling inner zone near the shaft and a more turbulent outer zone. The overall blend time is longer in the baffled tank at the same rotational speed compared to the baffled tank. This difference decreases with increasing Reynolds Number. We identified two blend times in using unbaffled tanks, a short blend time for the outer zone and a much longer time for the inner vortex centered zone which defines the overall blend time for the vessel. At low Reynolds Numbers the baffled blending is in the transitional flow regime between turbulent and laminar with a combination of eddies and striations. The last region of the tank to become completely mixed is located behind the baffles. Unbaffled blend times are shorter and as the Reynolds Number decreases the difference increases. The vortex is also reduced with decreasing Reynolds number. We consider this work just a beginning step in a long study and hope this work will be picked up by other researchers as happened so many times with Professor Nienow’s work.

Slurry flow characteristics control of 3D printed ceramic core layered structure: Experiment and simulation

Vat photopolymerization 3D printing ceramic technology provides a feasible process for the preparation of complex internal cooling channels for aeroengine single crystal superalloy hollow blades. However, the typical layered structure characteristics of 3D printing ceramic technology led to the anisotropy of ceramic core strength and sintering shrinkage, which greatly affects the performance and accuracy of the complex structure core and requires further research and improvement. Herein, the influence of the thickness of the slurry layer on the flow characteristics of the slurry in the process of the vat photopolymerization 3D printing slurry spreading was systematically studied by the method of simulation and experiment. The simulation results show that the positions of the turbulent zone and maximum velocity zone in the scraper front affect the redistribution of powder particles with different sizes. The layered structure was caused by the redistribution of ceramic particles of different sizes in the slurry layer. By controlling the turbulent flow zone and the maximum velocity zone of the scraper leading edge, the phenomenon of laminar flow can be weakened and the particle redistribution can be improved. With the increase of the thickness of the printing layer, the layered structure appears gradually, and the pores at the interface of the layered structure gradually concentrated into the interfacial pore lines from the uniform distribution, and the crack propagation changes from intergranular micro-crack to interlayer macro-crack. The combination of finite element simulation and experiment, through the slurry flow characteristics to control the layered structure of reductive vat photopolymerization ceramic core 3D printing, the control of crack propagation mode, element distribution and pore evolution of the core was accomplished, which lays a foundation for the performance control of ceramic 3D printing technology.

Turbulent convection as a significant hidden provider of magnetic helicity in solar eruptions

Solar flares and coronal mass ejections, the primary space weather disturbances affecting the entire heliosphere and near-Earth environment, mainly emanate from sunspot regions harbouring high degrees of magnetic twist. However, it is not clear how magnetic helicity, the quantity for measuring the magnetic twist, is supplied to the upper solar atmosphere via the emergence of magnetic flux from the turbulent convection zone. Here, we report state-of-the-art numerical simulations of magnetic flux emergence from the deep convection zone. By controlling the twist of emerging flux, we find that with the support of convective upflow, the untwisted emerging flux can reach the solar surface without collapsing, in contrast to previous theoretical predictions, and eventually create sunspots. Because of the turbulent twisting of magnetic flux, the produced sunspots exhibit rotation and inject magnetic helicity into the upper atmosphere, amounting to a substantial fraction of injected helicity in the twisted cases that is sufficient to produce flare eruptions. This result indicates that the turbulent convection is responsible for supplying a non-negligible amount of magnetic helicity and potentially contributes to solar flares.

Mathematical modeling of experiments on the interaction of a high-power ultraviolet laser pulse with condensed targets

Objectives. The paper aimed to review and analyze the results of works devoted to numerical modeling of experiments on the interaction of high-power ultraviolet (UV) laser pulses with condensed targets. The experiments were carried out at GARPUN, the powerful KrF-laser facility at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences (Moscow). The relevance of the research is related to the use of excimer UV lasers as a driver for a thermonuclear reactor. Physical aspects of laser-plasma interaction, including those related to the possibility of using two-sided cone target in a fission-fusion reactor, are discussed.Methods. The research is based on physico-mathematical models, including Euler and Lagrange.Results. The mathematical modeling of three types of natural experiments is presented: (1) burning through different thicknesses of Al foils by high-power UV laser; (2) studying hydrodynamic instability development at the UV laser acceleration of thin polymer films and features of turbulent zone formation; (3) interaction of high-power UV laser pulses with two-layer targets (Al + Plexiglas) and study of fine structures. Numerical modeling showed that a hybrid reactor with UV laser driver can use targets in the form of two-sided counter cones.Conclusions. Physico-mathematical models are developed along with 2D codes in Lagrangian and Eulerian coordinates as confirmed in the results of natural experiments. The models can be used to describe the physics of high-power UV laser pulses interacting with various targets and forecast the results of reactor-scale experiments.

NN‐MLT Model Prediction for Low‐Latitude Region Based on Artificial Neural Network and Long‐Term SABER Observations

AbstractThe low‐latitude mesosphere and lower thermosphere (MLT) regions are distinct and, highly turbulent transition zones in Earth's atmosphere. The scarcity of reliable measurements makes continuous monitoring of these areas challenging. Therefore, the necessity for studies focused on the MLT region cannot be overstated, as they are essential for developing effective models that meet the accuracy requirements of satellite‐based observations. The neural networks NN‐MLT model, developed using 15 years of Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics/satellite, equipped with Broadband Emission Radiometry (SABER) observed temperature data spanning from January 2006 to December 2020, employs neural network techniques. The data set was split, with 90% used for training and the remaining 10% allocated for prediction. The model's validation was tested with two other partitions (80(20) and 70(30)). The 90(10) partition, exhibiting a high correlation coefficient (R), low standard deviation (σ), and low root mean square error (RMSE), demonstrated the model's good performance. As clearly shown from statistical metrics (R, RMSE, mean, and σ) at three specific altitude levels (60, 75, and 90 km), the NN‐MLT model's performance aligns closely with the empirical model (NRLMSISE2‐0) and SABER observations. The NN‐MLT model displays a high R (0.74) and low RMSE (4.35 K) at 60 km, indicating its effective performance compared to the other two heights of 75 and 90 km. The NN‐MLT model's spatiotemporal variability in MLT temperature prediction agrees well with the SABER data at all altitudes, particularly at 60 km. While the NN‐MLT model accurately captures the seasonal variations of MLT temperature, the analysis leads to the conclusion that it consistently outperforms the empirical model and aligns closely with observations.

Effect of sneeze flow velocity profiles on the respiratory droplets dispersion in a confined space: An experimental and computational fluid dynamics study

In this study, the effects of sneeze velocity profiles, including peak velocity (PV), peak velocity time (PVT), and sneeze duration time (SDT), on the dispersion of respiratory droplets were studied experimentally and numerically. Spatial–temporal datasets of droplet velocity exhaled from several subjects' mouths with different physiological characteristics were obtained by particle image velocimetry. A direct relationship was found between the forced vital capacity and PV, while the subject's body mass index significantly affected the SDT. A transient computational fluid dynamics (CFD) approach using the renormalization group k–ε turbulence model in conjunction with the Lagrangian particle tracking was developed and used to simulate sneeze droplet motion characteristics. Both one-way and two-way (humidity) coupling models were used in these simulations. The CFD results showed that the two-way (humidity) coupling model provided better agreement with the data in the turbulent and expanded puff zones than the one-way coupling model. The one-way model led to reasonably accurate results in the fully dispersed and dilute-dispersed droplet phases. The effect of injection duration time and injection angle on PVT was larger than that on PV values, while the effect of initial injection velocity on PV was higher than that on PVT values. In addition, the initial injection velocity and angle significantly affected the maximum spreading distance of droplets dmax,sp. The numerical results obtained from the dilute-dispersed droplet phase were in good agreement with the trajectories of isolated droplets in the experimental data. The findings of this study provide novel insights into the effect of sneeze velocity profiles on dmax,sp, and the sneezer subject physiological effect on the threshold distance for the transmission of respiratory pathogens in a confined space.

Wind Pressure Orthogonal Decomposition Anemometer: A Wind Measurement Device for Multi-Rotor UAVs

Wind speed and direction are critical meteorological elements. Multi-rotor unmanned aerial vehicles UAVs are widely used as a premium payload platform in meteorological monitoring. The meteorological UAV is able to improve the spatial and temporal resolution of the elements collected. However, during wind measurement missions, the installed anemometers are susceptible to interference caused by rotor turbulence. This paper puts forward a wind pressure orthogonal decomposition (WPOD) strategy to overcome this limitation in three ways: the location of the sensors, a new wind measurement method, and supporting equipment. A weak turbulence zone (WTZ) is found around the airframe, where the turbulence strength decays rapidly and is more suitable for installing wind measurement sensors. For the sensors to match the spatial structure of this area, a WPOD wind measurement method is proposed. An anemometer based on this principle was mounted on a quadrotor UAV to build a wind measurement system. Compared with a standard anemometer, this system has satisfactory performance. Analysis of the resulting data indicates that the error of the system is ±0.3 m/s and ±2° under hovering conditions and ±0.7 m/s and ±5° under moving conditions. In summary, WPOD points to a new orientation for wind measurement under a small spatial–temporal scale.

Experimental analysis of thermal performance factor for double pipe heat exchanger with ZnO–water nanofluid

Nanofluid has attracted a large number of researchers in recent decades due to its exceptional heat transfer properties. In this study, a ZnO–H2O nanofluid with surfactant sodium dodecyl benzene sulphonate has been investigated to quantify heat transfer and frictional loss in a double-pipe heat exchanger. The turbulent zone was studied, with Reynolds numbers ranging from 5500 to 16,000 for fully developed flow. Volume fractions employed were 0.005%, 0.01%, 0.03% and 0.06%. Brownian motion and the interfacial layer, in addition to thermal conductivity, are the primary factor to influence heat transfer in heat exchangers. The maximum enhancement in Nusselt number and thermal performance achieved for a volume fraction of 0.06% at Reynolds number 5500 is 35% and 1.15, respectively.

Experimental research on effect of zonal heating airfoil about boundary layer flow and heat transfer

The anti-icing of aircraft and large wind turbines, where the wall temperature is higher than the fluid temperature, can significantly alter the flow evolution characteristics of the boundary layer. Local heating strategies for the manifold state need to be designed based on the changing characteristics of the flow velocity and temperature field in order to precisely control the heat supply and reduce inefficient energy consumption. In order to obtain accurate heat transfer characteristics of the airfoil’s boundary layer flow, it is necessary to refine the measurement of the boundary layer characteristics during flow and heat transfer. In this paper, wind tunnel experiments are carried out on the NACA2412 model with full surface’s zonal electric heating. The wall surface is equipped with a built-in heater and the temperature of the wall surface is obtained through the corresponding temperature sensor. By studying layer characteristics of the four heated regions, namely the laminar flow region near leading edge, the laminar flow destabilisation region, the transition region and the fully turbulent flow region, and comparing them with the boundary layer characteristics of the unheated airfoil, the effects of the presence of heat sources in different regions on the stability of the flow field and the spatial heat transfer pattern are revealed. The results show that heating in the laminar and turbulent zones maintains the stability of the flow field to a greater extent and achieves better heat transfer strength, while heating in the unstable zone brings forward the turbulence and heating in the fully turbulent zone intensifies the flow separation at the trailing edge of the airfoil. This study can be used as a reference for the design of efficient anti-icing systems on full wing surfaces.

Possibility of Clear Air Turbulence Localization with Lidar

The ranges of the parameters of wind and temperature (refractive) turbulence are estimated corresponding to the four-point scale of turbulence intensity at flight altitudes in the free atmosphere. It is shown that the estimates of both the variance of the radial velocity measured with a coherent lidar in the flight direction and of the structural constant of the refractive index from the lidar measurements of the intensity of refractive turbulence in the flight direction make it possible to judge the potential danger of bumpy flight of aircraft in clear-air turbulence zones ahead of the aircraft.

DNS of heat transfer in a plane channel flow with spatial transition

In the present work Direct Numerical Simulation of heat transfer in a spatial laminar-turbulent transitional channel flow is carried out to investigate the effects of the transitional phenomenon in the temperature field. The configuration is a spatially developing channel flow with two thermal boundary conditions: Uniform Wall Temperature (UWT) and Uniform Heat Flux (UHF). The set of simulations are carried out for Re=4200 and Pr=0.1,0.2,0.5,0.71 and 1. The spatial evolution of the Nusselt number (Nu) along the transition is computed to show five distinctive qualitative zones: a laminar development, the spike zone, where the quantities evolve to reach the peak transitional zone, the post-transitional zone and finally, the fully turbulent zone. This data is employed to develop a correlation that captures the space evolution of Nu along the transition. Moreover, the analysis of flow structures shows that near the wall and downstream the onset of the transition, streaks of velocity and temperature fluctuations have strong similarity. Different turbulent statistics are calculated along the transition and compared with fully turbulent reference data. It is shown that upstream the peak transitional zone, the existence of coherent hairpin vortices yields a high-intensity region for these quantities. Additionally, it is found that the thermal boundary condition exerts influence on the profile of the second-order parameters near the wall and in the logarithmic region all along the transition.

Changing the Paradigm of Environmental Law in a New Reality

This paper is an attempt to build a different paradigm of environmental law in the conditions of the planetary transformation of the Earth in the context of such civilizational paradigms as archaic — modern — postmodern — supermodern with the transition to the sixth technological order. These realities require both traditional and innovative legal regulation. The spectrum of transformations includes the initial parameters of the current order, the hierarchy of structures and the dynamics of their interaction, the level of fluctuation and bifurcation vectors, as well as attractors for exiting the turbulence zone. In order to answer these questions, the authors monitor previous and current environmental and historical trends in the world and the goal setting of what we are building in response to the challenges of the future on the basis of expanding interdisciplinary horizons, a systematic approach, a new range of methodologies and conceptual and categorical apparatus. Through the method of multidimensional didactics, legal topics are associatively connected to the consonant tasks of other subject areas with logical structuring and analysis of isomorphic meanings and semantic models for optimal synthesis of the developed legal systems with ensuring their applied effectiveness and practical application options. Interdisciplinary registers make it possible to build a new ecological and legal doctrine with the correction of the mutual importance of man and nature in the conditions of the global collapse of the capitalist system, based on impoverished natural resources and an increasing ecological catastrophe. Since it is necessary to go to the capital coordinates of the living cosmos for earthly problems to be solved, the «reasonable man» has completed a purely earthly cycle of evolution and must position himself as a «Universal Man» with access to a new ecological political and legal paradigm. These should include formulas (semantic images), integrals (keys of wholeness) and algorithms (methods of action, ways achievements) rule-making matrices.

Effects of Fire Location and Forced Air Volume on Fire Development for Single-Ended Tunnel Fire with Forced Ventilation

Single-ended tunnels are a typical structure and an important part during tunnel construction. In the case of a fire in a single-ended tunnel, forced ventilation is commonly used to create a safe area near the excavation face. This work is aimed at examining the effects of fire location and air volume on fire development for single-ended tunnel fires with forced ventilation. A single-ended tunnel was built in Fire Dynamics Simulator (FDS), and twenty simulation tests were carried out. In the simulation, the distribution of flow field, temperature, and CO concentration in the tunnel were measured and analyzed. The results show that three regions can be identified based on airflow directions and velocity: (1) turbulent flow zone, (2) turbulent flow transition zone, and (3) steady flow zone. It was found that the maximum ceiling temperature rise decreases first with the distance between the fire source and the excavation face (XL), and then increases with a further increase in XL. The simulation results also showed that CO can easily accumulate on the ventilation duct side at the fire source position and the opposite side of the ventilation duct 5.0–15.0 m downstream of the fire source. Both the CO concentration and the maximum ceiling temperature rise decrease with increasing air volume, while the larger forced air volume will result in a higher risk for the downstream regions. The present results are of practical importance in firefighting and personnel evacuation in single-ended tunnels with a forced ventilation system.

Numerical investigation of heat transfer augmentation and frictional loss characteristics in heat exchanger tube with the use of novel perforated rectangular cut twisted tape

ABSTRACT This paper focuses on augmentation of heat transfer and thermal performance factor of tubular heat exchanger by using a novel Perforated Rectangular Cut Twisted Tape (PRCTT) and comparison was made with Plain Tube (PT), Simple Twisted Tape (STT) and Rectangular Cut Twisted Tape (RCTT). Analysis of Nusselt number and friction factor for the twisted tape insert having twist ratio (TR) of 3, rectangular cuts of 2 mm width and 1 mm depth is done. Rectangular cuts of different pitch, that is, 3 mm, 5 mm and 7 mm is used for the analysis. To reduce the friction factor, further analysis has been done with perforation of circular hole in the same RCTT with perforation ratio (d/w) of 0.55 in the core of insert. Numerical analysis shows that in turbulent zone (4000<Re > 16000), highest enhancement in Nusselt number is 2.3 times and highest enhancement of friction factor by 3.2 times with comparison to plain tube when reducing the pitch of rectangular cuts. Perforation further decreases the friction factor by 20%. Highest thermal performance factor is observed 1.48 with the use of Perforated Rectangular Twisted Tape (PRCTT) at Re = 4000.

One-dimensional turbulence modeling of compressible flows: II. Full compressible modification and application to shock–turbulence interaction

One-dimensional turbulence (ODT) is a simulation methodology that represents the essential physics of three-dimensional turbulence through stochastic resolution of the full range of length and time scales on a one-dimensional domain. In the present study, full compressible modifications are incorporated into ODT methodology, based on an Eulerian framework and a conservative form of the governing equations. In the deterministic part of this approach, a shock capturing scheme is introduced for the first time. In the stochastic part, one-dimensional eddy events are modeled and sampled according to standard methods for compressible flow simulation. Time advancement adjustments are made to balance comparable time steps between the deterministic and stochastic parts in compressible flows. Canonical shock–turbulence interaction cases involving Richtmyer–Meshkov instability at Mach numbers 1.24, 1.5, and 1.98 are simulated to validate the extended model. The ODT results are compared with available reference data from large eddy simulations and laboratory experiments. The introduction of a shock capturing scheme significantly improves the performance of the ODT method, and the results for turbulent kinetic energy are qualitatively improved compared with those of a previous compressible Lagrangian ODT method [Jozefik et al., “Simulation of shock–turbulence interaction in non-reactive flow and in turbulent deflagration and detonation regimes using one-dimensional turbulence,” Combust. Flame 164, 53 (2016)]. For the time evolution of profiles of the turbulent mixing zone width, ensemble-averaged density, and specific heat ratio, the new model also yields good to reasonable results. Furthermore, it is found that the viscous penalty parameter Z of the ODT model is insensitive to compressibility effects in turbulent flows without wall effects. A small value of Z is appropriate for turbulent flows with weak wall effects, and the parameter Z serves to suppress extremely small eddy events that would be dissipated instantly by viscosity.

A thick reaction zone model for premixed flames in two-dimensional channels

Direct interactions between the flow field and the chemical reaction in premixed flames occur when the reaction zone thickness is comparable to, or greater than flow length scales. To study such interactions, a laminar model is considered that has direct bearings to steadily propagating deflagrations in a Hele-Shaw channel with a background plane Poiseuille flow. The study employs asymptotic analyses, pertaining to large activation energy and lubrication theories and considers a distinguished limit where the channel width is comparable to the reaction zone thickness, with account being taken of thermal-expansion and heat-loss effects. The reaction zone structure and burning rates depend on three parameters, namely, the Peclet number, , the Lewis number, and the ratio of channel half-width to reaction zone thickness, . In particular, when the parameter is small wherein the reaction zone is thick, transport processes are found to be controlled by Taylor's dispersion mechanism and an explicit formula for the effective burning speed is obtained. The formula indicates that for , which interestingly coincides with a recent experimental prediction of the turbulent flame speed in a highly turbulent jet flame. The results suggest that the role played by differential diffusion effects is significant both in the laminar and turbulent cases. The reason for the peculiar dependence can be attributed, at least in our laminar model, to Taylor dispersion. Presumably, this dependence may be attributed to a similar but more general mechanism in the turbulent distributed reaction zone regime, rather than to diffusive-thermal curvature effects. The latter effects play however an important role in determining the effective propagation speed for thinner reaction zones, in particular, when is large in our model. It is found that the magnitude of heat losses at extinction, which directly affects the mixture flammability limits, is multiplied by a factor in comparison with those corresponding to the no-flow case in narrow channels.