Horizontal Concentration Gradients Research Articles

Using open-path dual-comb spectroscopy to monitor methane emissions from simulated grazing cattle

Abstract. Accurate whole-farm or herd-level measurements of livestock methane emissions are necessary for anthropogenic greenhouse gas inventories and to evaluate mitigation strategies. A controlled methane (CH4) release experiment was performed to determine if dual-comb spectroscopy (DCS) can detect CH4 concentration enhancements produced by a typical herd of beef cattle in an extensive grazing system. Open-path DCS was used to measure downwind and upwind CH4 concentrations from 10 point sources of methane simulating cattle emissions. The CH4 mole fractions and wind velocity data were used to calculate CH4 flux using an inverse dispersion model, and the simulated fluxes were then compared to the actual CH4 release rate. For a source located 60 m from the downwind path, the DCS system detected 10 nmol mol−1 CH4 horizontal concentration gradient above the atmospheric background concentration with a precision of 6 nmol mol−1 in 15 min interval. A CH4 release of 3970 g d−1 was performed, resulting in an average concentration enhancement of 24 nmol mol−1 of CH4. The calculated CH4 flux was 4002 g d−1, showing good agreement with the actual CH4 release rate. Periodically altering the downwind path, which may be needed to track moving cattle, did not adversely affect the ability of the instruments to determine the CH4 flux. These results give us confidence that CH4 flux can be determined by grazing cattle with low disturbance and direct field-scale measurements.

Effect of surface radiation on double diffusion convection in a low Mach number compressible gaseous mixture (H2–air)

This study aims to numerically investigate the effect of surface radiation on double diffusion convection in a low Mach number compressible gaseous mixture, specifically focusing on the H2–air system in a square cavity. The cavity is subjected to low horizontal temperature and concentration gradients and isolated from its flat walls. The mathematical model's equations were discretized using the finite volume method based on the semi-implicit method for pressure-linked equations revised algorithm for the pressure–velocity coupling. The radiosity method is employed to calculate the radiative heat exchange between the internal walls of the cavity. This work addresses a significant research gap by exploring the interplay between surface radiation, compressibility effects, and double diffusion convection. It makes a novel contribution to the field and has implications for combustion, astrophysics, and industrial heat exchange processes. Comparing the results with those obtained for a light gaseous mixture, the findings demonstrate that the presence of radiation considerably modifies the thermal, dynamic, and mass fields, as well as the thermophysical properties of the gaseous mixture in the case of heavy gaseous mixtures. These modifications can reach up to 20%.The outcomes of this study provide a foundation for further research and experimentation, with applications ranging from engineering to astrophysics.

Stability of the double-diffusive convection generated through the interaction of horizontal temperature and concentration gradients in the vertical slot

Previously, the double-diffusive convection (or the DDC) generated through the interaction between horizontal temperature and concentration gradients had been investigated by both experimental and computational studies. In the present study, we employ a theoretical approach by performing linear stability analysis to examine the stability characteristics of the DDC under a wide range of physical parameters. Results show that, under the competition between the two gradients, the stability can be discerned into thermal, salt-finger, and diffusive types, where all are influenced by both the Prandtl number Pr and Lewis number Le. The onset of instability can be the stationary shear mode (or the SSM) or the oscillatory buoyant mode (or the OBM), depending on both Pr and Le. Specifically, for the solute Grashof number Gs < 10, the onset of instability changes from SSM to OBM at the transition boundary Pr = 12.5; for the thermal Grashof number Gt < 10, the transition boundary is governed by the relation Pr = 12.5Le−1.11 + 0.46. We compare the present results with those of previous studies to justify the linear stability analysis’s correctness and infer that the DDCs observed by previous experiments and nonlinear computations are nonlinear salt-finger convection.

Firework smoke: Impacts on urban air quality and deposition in the human respiratory system

Particle number concentrations and size distributions resulting from the firework displays held in Budapest, Hungary every year on St. Stephen's Day were studied over a period of seven years. In the year most impacted, the total particle number concentration reached its peak measured level of 369 × 103 cm−3 5 min after the end of the display, and returned to the pre-event state within 45 min. The fireworks increased hourly mean concentrations by a factor of 5–6, whereas the concentrations in the diameter range of 100–1000 nm, in which the magnitude of the increase was the greatest, were elevated by a factor of 20–25. An extra particle size mode at 203 nm was manifested in the size distributions as result of the fireworks. The PM10 mass concentrations at peak firework influence and as 1-h mean increased 123 and 58 times, respectively, relative to the concentration before the display. The smoke was characterised by a relatively short overall atmospheric residence time of 25 min. Spatiotemporal dispersion simulations revealed that there were substantial vertical and horizontal concentration gradients in the firework plume. The affected area made up a large part of the city. Not only the spectators of the display at the venue and nearby areas, but the population located further away downwind of the displays and more distant, large and populous urban quarters were affected by the plume and its fallout. The fireworks increased the deposition rate in the respiratory system of females by a factor of 4, as a conservative estimate. The largest surface density deposition rates were seen in the segmental and sub-segmental bronchi, which represents an excessive risk to health. Compared to adults, children were more susceptible to exposure, with the maximum surface density deposition rates in their case being three times those of adults in the trachea.

Natural double-diffusive convection for the Carreau shear-thinning fluid in a square cavity submitted to horizontal temperature and concentration gradients

• The paper investigated double-diffusive convection of a shear-thinning fluid. • All parameters of the Carreau model influence the convective flows. • When Ra T very high, the Carreau and power-law models give almost the same results. • The results of scale analysis and numerical solution are in good agreement. We study heat and mass transfers by natural convection for shear-thinning non-Newtonian binary fluids confined in a square cavity. Thermal and solutal boundary conditions of the Dirichlet type are applied on the vertical walls of the cavity while the horizontal ones are assumed adiabatic and impermeable. We used the rheological Carreau model, adequate for many non-Newtonian fluids to characterize the shear-thinning behavior. The first part from this study is devoted to the numerical solution of the governing equations, and the effect of the governing parameters, namely, the thermal Rayleigh number Ra T , Prandtl number Pr , Lewis number Le , buoyancy ratio N and the various parameters of Carreau model. Numerical calculations are also carried out by considering the same problem on the basis of the power-law model, and a comparison of the results predicted by the two rheological models is performed. In the second part, a scale analysis is proposed to obtain correlations giving the heat and mass transfers. The results of this approach are validated numerically and a good agreement is found between the two methods.

Numerical study of magnetic field effect on natural convection heat and mass transfers in a square enclosure containing non-Newtonian fluid and submitted to horizontal temperature and concentration gradients

Numerical study of magnetic field effect on natural convection heat and mass transfers in a square enclosure containing non-Newtonian fluid and submitted to horizontal temperature and concentration gradients

Magnetic Field Effect on Multiplicity of Solutions Induced by Thermosolutal Convection in a Bénard Square Porous Cavity Submitted to Horizontal Concentration Gradient

In this work, we present a numerical study of the magnetic field effect on double diffusive natural convection in a square porous cavity saturated with an electrically conducting binary mixture. The cavity is heated from below and cooled from the top, while its vertical walls are adiabatic and maintained at constant but different concentrations. The numerical results are obtained for a Lewis number Le = 10 and the following ranges for the other controlling parameters: 40 ≤ RT ≤ 1000, -0.2 ≤ N ≤ 0.2 and -0.5 ≤ Ha ≤ 0.5, where RT, N and Ha are the thermal Rayleigh number, the buoyancy ratio and the Hartmann parameter, respectively. First, the effect of the Hartmann parameter on the maintenance and disappearance of the multiple steady state solutions obtained in the case of purely thermal convection is examined. Then, the combined effect of N and Ha on the existence of these steady solutions is analyzed. It is found that the critical values of N corresponding to the transitions between the different solutions are modified by the application of a magnetic field. However, the nature of the transitions is unchanged. It is shown that the magnetic field may affect considerably the flow intensity and the heat and mass transfer in the medium.

Simulating the forest fire plume dispersion, chemistry, and aerosol formation using SAM-ASP version 1.0

Abstract. Biomass burning is a major source of trace gases and aerosols that can ultimately impact health, air quality, and climate. Global and regional-scale three-dimensional Eulerian chemical transport models (CTMs) use estimates of the primary emissions from fires and can unphysically mix them across large-scale grid boxes, leading to incorrect estimates of the impact of biomass burning events. On the other hand, plume-scale process models allow for explicit simulation and examination of the chemical and physical transformations of trace gases and aerosols within biomass burning smoke plumes, and they may be used to develop parameterizations of this aging process for coarser grid-scale models. Here we describe the coupled SAM-ASP plume-scale process model, which consists of coupling the large-eddy simulation model, the System for Atmospheric Modelling (SAM), with the detailed gas and aerosol chemistry model, the Aerosol Simulation Program (ASP). We find that the SAM-ASP version 1.0 model is able to correctly simulate the dilution of CO in a California chaparral smoke plume, as well as the chemical loss of NOx, HONO, and NH3 within the plume, the formation of PAN and O3, the loss of OA, and the change in the size distribution of aerosols as compared to measurements and previous single-box model results. The newly coupled model is able to capture the cross-plume vertical and horizontal concentration gradients as the fire plume evolves downwind of the emission source. The integration and evaluation of SAM-ASP version 1.0 presented here will support the development of parameterizations of near-source biomass burning chemistry that can be used to more accurately simulate biomass burning chemical and physical transformations of trace gases and aerosols within coarser grid-scale CTMs.

Uncertainty quantification and global sensitivity analysis of double-diffusive natural convection in a porous enclosure

In this paper, detailed uncertainty propagation analysis (UPA) and variance-based global sensitivity analysis (GSA) are performed on the widely adopted double-diffuse convection (DDC) benchmark problem of a square porous cavity with horizontal temperature and concentration gradients. The objective is to understand the impact of uncertainties related to model parameters on metrics characterizing flow, heat and mass transfer processes, and to derive spatial maps of uncertainty and sensitivity indices which can provide physical insights and a better understanding of DDC processes in porous media. DDC simulations are computationally expensive and UPA and GSA require large number of simulations, so an appropriate strategy is developed to reduce the computational burden. The approach is built on two pillars: (a) an efficient numerical simulator based on the Fourier series method that generates training data, and (b) polynomial chaos expansion (PCE) meta-models that are trained using the simulator data, and then replace the numerical model in UPA and GSA. Assuming that the Rayleigh number (Ra), the solutal to thermal buoyancy ratio (Nb) and the Lewis number (Le) are the uncertain input variables, the results of UPA show that the zones of high temperature and concentration variability are located in the regions where the flow is mainly driven by the buoyancy effects. GSA indicates that Nb is the most influential parameter affecting the temperature and concentration fields, followed respectively by Ra and Le. For the heat-driven flow case (Nb>−1), the concentration field is more influenced by Le than Ra. For deeper understanding of uncertainty propagation, we estimate the bias introduced by replacing uncertain parameters by deterministic values. The resulting spatial maps of the difference between deterministic output and stochastic mean show that a deterministic approach leads to different zones where the temperature, concentration and velocity fields can be either overestimated or underestimated. The conclusions drawn in this work are likely to be helpful in different applications involving DDC in porous enclosures leading to convective circulation cells.

Comparison of diffusion tube\u2013measured nitrogen dioxide concentrations at child and adult breathing heights: who are we monitoring for?

Many towns and cities use passive samplers (diffusion tubes) to monitor nitrogen dioxide (NO2) concentration. However, literature studies have shown large horizontal and vertical concentration gradients for diffusion tubes placed over short distances, raising concerns over the representativeness of monitoring locations. This study examines variations in NO2 concentrations with height at two roadside locations along a busy urban road in Newcastle upon Tyne (UK) over an 8-month period. NO2 concentrations were passively monitored at building facades (approximately 7.0 m from the roadside) at heights of 0.7 m, 1.7 m and 2.7 m to replicate child breathing height in prams and buggies, adult breathing height and the Newcastle City Council sampling height (for 2017), respectively. Paired t tests indicated that NO2 concentrations were significantly lower at 2.7 m (4.7% lower, n = 16, p = 0.001) and 1.7 m (7.1% lower, n = 14, p = 0.007) compared with those at 0.7 m. There was no statistically significant difference between NO2 concentrations measured at 2.7 m and 1.7 m, indicating that UK local authority practice of placing diffusion tubes at higher than adult breathing height does not result in underreporting of NO2 concentrations for regulatory purposes. The results have clear public health implications as they provide evidence that young children, in an urban setting and close to busy roadways, may be exposed to higher NO2 concentrations compared with adults in the same location. We have shown that such differences might not be adequately reflected in the monitoring data from municipal authorities.

Continuous-Flow Nanoparticle Trapping Driven by Hybrid Electrokinetics in Microfluidics.

We introduce herein an efficient microfluidic approach for continuous transport and localized collection of nanoparticles via hybrid electrokinetics, which delicately combines linear and nonlinear electrokinetics driven by a composite DC-biased AC voltage signal. The proposed technique utilizes a simple geometrical structure, in which one or a series of metal strips serving as floating electrode (FE) are attached to the substrate surface and arranged in parallel between a pair of coplanar driving electrodes (DE) in a straight microchannel. On application of a DC-biased AC electric field across the channel, nanoparticles can be transported continuously by DC bulk electroosmotic flow, and then trapped selectively onto the metal strips due to AC-field induced-charge electrokinetic (ICEK) phenomenon, which behaves as counter-rotating micro-vortices around the ideally polarizable surfaces of FE. Finite-element simulation is carried out by coupling the dual-frequency electric field, flow field and sample mass transfer in sequence, for guiding a practical design of the microfluidic nanoparticle concentrator. With the optimal device geometry, the actual performance of the technique is investigated with respect to DC bias, AC voltage amplitude, and field frequency by using both latex nanospheres (∼500nm) and BSA molecules (∼10nm). Our experimental observation indicates nanoparticles are always enriched into a narrow bright band on the surface of each FE, and a horizontal concentration gradient even emerges in the presence of multiple metal strips, which therefore permits localized analyte enrichment. The proposed trapping method is supposed to guide an elaborate design of flexible electrokinetic frameworks embedding FE for continuous-flow analyte manipulation in modern microfluidic systems.

The Effect of Magnetic Field on the Stability of Double-Diffusive Convection in a Porous Layer with Horizontal Mass Throughflow

The onset of double-diffusive convection in an electrically conducting fluid-saturated porous layer is studied. The convective flow in the porous medium is induced by horizontal temperature and concentration gradients with net horizontal mass throughflow. The effect of magnetic field on the instability of convection is taken into consideration. The stability of the steady-state solution is investigated in two different approaches, namely the linear instability analysis and nonlinear stability analysis. The nonlinear stability analysis is performed by constructing the energy functional. The eigenvalue problems which are derived from the stability analyses are numerically integrated using the shooting and Runge–Kutta methods. The variation in the critical thermal Rayleigh number against each flow governing parameter is shown graphically. It is observed that Hartman number $$Ha^{2}$$ delays the onset of convection to commence and helps to reduce the region of subcritical instabilities. When the solute is concentrated at lower boundary of the porous layer, the onset of convection is in the form of stationary modes, but it switches to oscillatory mode of convection when the solute is concentrated at upper boundary. Interestingly, Hartman number $$Ha^{2}$$ plays an important role in delaying this transition from stationary mode to oscillatory mode of convection.

Solar-driven interfacial desalination for simultaneous freshwater and salt generation

Localized heating-based solar distillation has recently emerged as an efficient and facile way to generate freshwater out of saline water. Salt fouling, however, remains a fundamental challenge to stable operation of the desalination system, in particular for high-salinity brine. Here we demonstrate a solar-driven interfacial evaporation-based desalination structure, which achieves localized surface salt precipitation through mediating the horizontal salt concentration gradient within the printed paper-based solar absorber, to minimize salt fouling while maintaining heat localization. With optimized design, such desalination system achieves a stable evaporation efficiency of ~78% under 1100 W m−2 solar illumination, and simultaneously generates drinkable water out of 10 wt% brine with a solar-to-water conversion efficiency more than 40% and NaCl salts with higher productivity over conventional bulk heating-based salt farm technology. This low-cost, environmentally-friendly, bifunctional desalination technology not only helps solve the salt fouling issue but also holds the potential to offer a new way to extract minerals from seawater.

Complex transition of double-diffusive convection in a rectangular enclosure with height-to-length ratio equal to 4: Part II

The paper investigates numerical results of double-diffusive convection in a slim rectangular enclosure with horizontal temperature and concentration gradients. The case with the thermal Rayleigh number, RaT=105, the Prandtl number, Pr=1, the Lewis number, Le=2 and height-to-width aspect ratio, A=4 is considered. Effects of the buoyancy ratio of composition to temperature, N, on dynamical behavior, flow structure and heat and mass transfer efficiency are investigated carefully. The present results suggest that with the buoyancy ratio N increasing from 1 to 2, the flow of transition is a complex series of changes from the periodic to quasi-periodic, chaotic, periodic, and finally to laminar with concentration dominated. There are three types of periodic flows, the first one is simple periodic flow with single fundamental frequency (FF), the second one is periodic flow with FF and its integer multiple of frequencies (INTMF), the last one is the more complex periodic flow with FF, INTMF and its sub-harmonic frequency multiple (SFM). A new type periodical solution with reverse central symmetrical structure is captured in the present paper. Multi cells structures traversing between two vertical walls will produce salt figure phenomenon and benefit to enhance heat and mass transfer efficiency.

The effect of acoustic wave on the stability of stationary convective flow of binary fluid in a horizontal layer subjected to horizontal temperature and concentration gradients

The effect of acoustic wave propagating in the direction of temperature gradient on a stability of stationary plane-parallel flow of binary fluid, generated by horizontal temperature and concentration gradients in a horizontal layer is investigated for two types of thermal boundary conditions: perfectly conductive and adiabatic boundaries. The study is performed analytically for the longwave perturbations and numerically for finite-wavelength perturbations. Stability maps for fixed Prandtl number value Pr=0.01 and different values of Schmidt number and acoustic Reynolds number are obtained. The most dangerous instability modes and critical perturbation structure are discussed. Comparison with the case where acoustic wave is absent is performed. It is shown, that longwave perturbations are always stabilized by acoustic wave. Numerical investigation demonstrates, that acoustic wave also stabilizes the flow with respect to finite-wavelength perturbations when negative concentrational Grashof number is higher in modulus than certain value depending on acoustic wave intensity.

Three-dimensional doubly diffusive convectons: instability and transition to complex dynamics

Three-dimensional doubly diffusive convection in a closed vertically extended container driven by competing horizontal temperature and concentration gradients is studied by a combination of direct numerical simulation and linear stability analysis. No-slip boundary conditions are imposed on all six container walls. The buoyancy number $N$ is taken to be $-1$ to ensure the presence of a conduction state. The primary instability is subcritical and generates two families of spatially localized steady states known as convectons. The convectons bifurcate directly from the conduction state and are organized in a pair of primary branches that snake within a well-defined range of Rayleigh numbers as the convectons grow in length. Secondary instabilities generating twist result in secondary snaking branches of twisted convectons. These destabilize the primary convectons and are responsible for the absence of stable steady states, localized or otherwise, in the subcritical regime. Thus all initial conditions in this regime collapse to the conduction state. As a result, once the Rayleigh number for the primary instability of the conduction state is exceeded, the system exhibits an abrupt transition to large-amplitude relaxation oscillations resembling bursts with no hysteresis. These numerical results are confirmed here by determining the stability properties of both convecton types as well as the domain-filling states. The number of unstable modes of both primary and secondary convectons of different lengths follows a pattern that allows the prediction of their stability properties based on their length alone. The instability of the convectons also results in a dramatic change in the dynamics of the system outside the snaking region that arises when the twist instability operates on a time scale faster than the time scale on which new rolls are nucleated. The results obtained are expected to be applicable in various pattern-forming systems exhibiting localized structures, including convection and shear flows.

Effects of Wind Speed and Wind Gustiness on Subsurface Gas Transport

Core Ideas Subsurface gas transport as related to near‐surface wind speed and gustiness was measured. Increased wind gustiness tended to decrease subsurface gas movement at greater depth. Horizontal gas concentration gradients and gas movement in the subsurface are important. Wind action appears to induce an advective gas flow pattern in the subsurface. The impact of near‐surface wind speed and wind speed fluctuations (gustiness) on subsurface gas transport and exchange with the atmosphere was investigated with a focus on assessing the extent of vertical and horizontal gas transport in the subsurface. Investigations involved the use of a 40‐ by 40‐cm, 35‐cm‐deep stainless steel container filled with a dry granular porous medium (2–4‐mm grain size), applying CO2 and O2 as tracer gases. Experiments were performed under controlled (laboratory) conditions for different wind speeds (0–5.6 m s−1) under both gusty and non‐gusty wind conditions. Horizontal gas movement in the porous medium both parallel and perpendicular to the wind direction was controlled via a set of separation walls that could be installed inside the porous medium to assess the importance of horizontal gas velocities in the porous medium. Results indicate that average wind speed was the most important parameter controlling porous medium gas transport, especially near the surface. However, at greater depths, wind gustiness and horizontal gas movement also had significant impacts on the overall gas transport.

A thermal non-equilibrium model for 3D double diffusive convection of power-law fluids with chemical reaction in the porous medium

The article reports a numerical study of the double-diffusive natural convection of power-law fluids in a porous cubic cavity with chemical reaction under the local thermal non-equilibrium (LTNE) state and submitted to horizontal temperature and concentration gradients. The complete governing equations, in which the generalized non-Darcy model is employed as momentum equation and a two-temperature model that represents temperature fields of the fluid and solid phases separately is used for energy equation, are solved by the compact high order finite volume method. Special attentions are given to detecting the effects of the porosity modified conductivity ratio (γ), the inter-phase heat transfer coefficient (H), the chemical reaction parameter (λ), the Dufour parameter (Du), the Soret parameter (Sr) and the Lewis number (Le) on the fluid flow as well as on rates of heat and mass transfer. Our simulations show that the heat transfer rate of solid increases, while the heat transfer rate of fluid and mass transfer rate keep constants, as the LTNE parameters (i.e., γ and H) increase. For any relatively large value of γ and H, the almost thermal equilibrium state is achieved due to the similar thermal distribution of fluid and solid phases. On the contrary, the chemical reaction parameter has significant influence on mass transfer than on heat transfer under the LTNE conditions. In addition, the heat and mass transfer enhance with the increment of the Soret and Dufour parameters. Augmentation of Lewis number enhances mass transfer but reduces heat transfer. Apart from that, our numerical tests show the flow field is influenced appreciably by the presence of the power-law index (n), Darcy number (Da) and porous thermal Rayleigh number (Ra).

Ammonia emissions from a grazed field estimated by miniDOAS measurements and inverse dispersion modelling

Abstract. Ammonia (NH3) fluxes were estimated from a field being grazed by dairy cattle during spring by applying a backward Lagrangian stochastic model (bLS) model combined with horizontal concentration gradients measured across the field. Continuous concentration measurements at field boundaries were made by open-path miniDOAS (differential optical absorption spectroscopy) instruments while the cattle were present and for 6 subsequent days. The deposition of emitted NH3 to clean patches on the field was also simulated, allowing both net and gross emission estimates, where the dry deposition velocity (vd) was predicted by a canopy resistance (Rc) model developed from local NH3 flux and meteorological measurements. Estimated emissions peaked during grazing and decreased after the cattle had left the field, while control on emissions was observed from covariance with temperature, wind speed and humidity and wetness measurements made on the field, revealing a diurnal emission profile. Large concentration differences were observed between downwind receptors, due to spatially heterogeneous emission patterns. This was likely caused by uneven cattle distribution and a low grazing density, where hotspots of emissions would arise as the cattle grouped in certain areas, such as around the water trough. The spatial complexity was accounted for by separating the model source area into sub-sections and optimising individual source area coefficients to measured concentrations. The background concentration was the greatest source of uncertainty, and based on a sensitivity/uncertainty analysis the overall uncertainty associated with derived emission factors from this study is at least 30–40 %.Emission factors can be expressed as 6 ± 2 g NH3 cow−1 day−1, or 9 ± 3 % of excreted urine-N emitted as NH3, when deposition is not simulated and 7 ± 2 g NH3 cow−1 day−1, or 10 ± 3 % of excreted urine-N emitted as NH3, when deposition is included in the gross emission model. The results suggest that around 14 ± 4 % of emitted NH3 was deposited to patches within the field that were not affected by urine or dung.

Numerical modeling of deflagration to detonation transition in inhomogeneous hydrogen/air mixtures

Explosions in homogeneous reactive mixtures have been widely studied both experimentally and numerically. However, in practice, combustible mixtures are usually inhomogeneous and subject to both vertical and horizontal concentration gradients. There is still very limited understanding of the explosion characteristics in such situations. The present study aims to investigate deflagration to detonation transition (DDT) in such mixtures. Two cases in a horizontal obstructed channel with 30% and 60% blockage ratios filled with hydrogen/air mixture with vertical concentration gradients are numerically studied. These cases were experimentally investigated by Boeck et al. (2015), and hence some measurements are available for model validation. A density-based solver within the OpenFOAM CFD toolbox is developed and used. To evaluate the convective fluxes contribution, the Harten–Lax–van Leer–Contact (HLLC) scheme is used for shock capturing. The compressible Navier–Stokes equations with a single step Arrhenius reaction are solved. The numerical results are in good qualitative and quantitative agreement with the experiments. The predictions show that the overpressure at the DDT transition stage is higher in the non-uniform mixtures than that in homogeneous mixtures under similar conditions. It is also found that increasing the blockage ratio from 30% to 60% resulted in faster flame propagation and lower propensity to DDT. The Baroclinic torque and the resulting Richtmyer–Meshkov (RM) instability are also analyzed in relation to flame acceleration and DDT.