Validation of leading point concept in RANS simulations of highly turbulent lean syngas-air flames with well-pronounced diffusional-thermal effects

While significant increase in turbulent burning rate in lean premixed flames of hydrogen or hydrogen-containing fuel blends is well documented in various experiments and can be explained by highlighting local diffusional-thermal effects, capabilities of the vast majority of available models of turbulent combustion for predicting this increase have not yet been documented in numerical simulations. To fill this knowledge gap, a well-validated Turbulent Flame Closure (TFC) model of the influence of turbulence on premixed combustion, which, however, does not address the diffusional-thermal effects, is combined with the\ua0 leading point concept, which highlights strongly perturbed leading flame kernels whose local structure and burning rate are significantly affected by the diffusional-thermal effects. More specifically, within the framework of the leading point concept, local con sumption velocity is computed in extremely strained laminar flames by adopting detailed combustion chemistry and, subsequently, the computed velocity is used as an input parameter of the TFC model. The combined model is tested in RANS simulations of highly turbulent, lean syngas-air flames that were experimentally investigated at Georgia Tech. The tests are performed for four different values of the inlet rms turbulent velocities, different turbulence length scales, normal and elevated (up to 10 atm) pressures, various H2/CO ratios ranging from 30/70 to 90/10, and various equivalence ratios ranging from 0.40 to 0.80. All in all, the performed 33 tests indicate that the studied combination of the leading point concept and the TFC model can predict well-pronounced diffusional-thermal effects in lean highly turbulent syngas-air flames, with these results being obtained using the same value of a single constant of the combined model in all cases. In particular, the model well predicts a significant increase in the bulk turbulent consumption velocity when increasing the H2/CO ratio but retaining the same value of the laminar flame speed

A LARGE EDDY SIMULATION STUDY OF THE EFFECTS OF WIND AND SLOPE ON THE STRUCTURE OF A TURBULENT LINE FIRE

Due to a complex coupling between a large number of physical and chemical processes that happen over a wide range of length and time scales, our current fundamental understanding of wildland fire spread is limited. Wildland fire spread is affected by many parameters, but two of the most important parameters are wind and slope both of which tilt the flame and plume and bring them closer to the unburnt fuel, which, among other things, increases the convective heat transfer and hence the spread rate. The primary objective of this work is to enhance our fundamental understanding of the effects of wind and slope on the structure of a turbulent, buoyant line fire. To meet the aforementioned objective we perform well-resolved Large Eddy Simulations (LES) of a simplified configuration corresponding to a turbulent, buoyant, methane-fueled, stationary, line fire and subjected to wind or slope. Simulations are performed with an LES solver developed by FM Global and called FireFOAM which is based on the OpenFOAM CFD library. For the cases with wind, the transition from the buoyancy-dominated (in which the flame and plume are mostly detached from the downwind surface and have a tilted vertical shape; entrainment is two-sided; downwind surfaces experience convective cooling) to wind-dominated (in which the flame and plume are attached to the downwind surface; entrainment is one-sided; downwind surfaces experience convective heating) regime happens when the Byram’s convection number Nc is ≈1. The flame and plume attachment lengths (defined as the x-wall-distance downwind of the burner within the flame and plume regions, respectively) are found to fluctuate significantly in time. For the cases with slope the transition from the detached regime (equivalent to the buoyancy-dominated regime) to the attached regime (equivalent to the wind-dominated regime) is found to happen between slopes of 16 and 32 degrees. Upslope of the flame zone, the velocity tangent to the surface is found to change from a relatively small negative value (≈ −0.3 m/s) to a relatively large positive value (≈ 2.5 m/s), when the slope is increased from 16 to 32 degrees. The flame attachment length (defined as the tangential-wall-distance upslope of the burner within the flame region) is again found to fluctuate significantly in time. An integral model, capable of describing the effects of cross-wind on the structure of a turbulent, buoyant line fire, is also developed in this work. The model, after some simplifications, suggests that the plume tilt angle is controlled by the Byram’s convection number Nc and the entrainment coefficients α and β. Detailed comparisons are made between the model and LES and show that the model performs well for the cases belonging to the buoyancy-dominated regime (Nc>1) but fails to describe the cases belonging to the wind-dominated regime (Nc<1) because of the absence of a wall attachment sub-model

Understanding flame structure in wildfires using Large Eddy Simulations

The structure of wildfire flames in the presence of crossflow was analyzed by utilizing suitable non-reacting numerical experiments with low speed flow over a hot isothermal horizontal semi-infinite surface. FireFOAM, a Large Eddy Simulation (LES) based solver developed by FM Global for fire protection engineering applications, was employed for all the calculations. Early-time dynamics of Rayleigh-Taylor Instability (RTI) was first simulated using Direct Numerical Simulations (DNS) so that the solver could be verified against Linear Stability Theory (LST). Then attention was given to late-time dynamics in order understand the different stages (e.g., appearance of secondary instability, generation of larger scales due to interaction between structures) involved in the development of the instability. The onset of thermal vortex instability, in a configuration with low speed flow over a hot isothermal semi-infinite horizontal plate, predicted using DNS was compared with the literature. Spatial evolution of various terms in the streamwise vorticity equation was used to identify the dominant mechanisms responsible for the generation/evolution of vorticity. Streamwise evolution of the instabilities was studied and the effects of the changes in temperature and orientation of the plate on the thermal instabilities were also investigated. Finally, a configuration with low speed flow over a hot isothermal semi-infinite horizontal strip was used to understand the effects of upstream Boundary Layer (BL) height and the length of the strip on both the thin horizontal and larger structures (analogous to Flame Towers (FT) observed in real wildfires and laboratory experiments)

Numerical simulation of droplet formation in a microchannel device

The formation of droplets is a phenomenon with particular importance in the development of industrial emulsions. The quality of these compounds is associated with droplet size and stability over time. Anna et al. (2003) developed a methodology named ¨flow focusing¨ to improve droplet formation processes for engineering applications. In this work, Computational Fluid Dynamics (CFD) based techniques are used to assess the capacity of a pseudo-2D numerical model to reproduce water droplets formation within silicon oil, as obtained in Anna et al.’s experiments. Average time of droplet onset obtained via numerical analysis was 1.5 times larger than observed experimentally, whereas droplets convection velocity and diameter predictions differed by 40-45% and 60%, respectively. Nevertheless, calculated velocity profiles downstream the discharge slot reproduced the expected free-jet shear layer according to outer/inner flow ratio

Numerical simulation of droplet formation in a microchannel device

The formation of droplets is a phenomenon with particular importance in the development of industrial emulsions. The quality of these compounds is associated with droplet size and stability over time. Anna et al. (2003) developed a methodology named ¨flow focusing¨ to improve droplet formation processes for engineering applications. In this work, Computational Fluid Dynamics (CFD) based techniques are used to assess the capacity of a pseudo-2D numerical model to reproduce water droplets formation within silicon oil, as obtained in Anna et al.’s experiments. Average time of droplet onset obtained via numerical analysis was 1.5 times larger than observed experimentally, whereas droplets convection velocity and diameter predictions differed by 40-45% and 60%, respectively. Nevertheless, calculated velocity profiles downstream the discharge slot reproduced the expected free-jet shear layer according to outer/inner flow ratio

Intravenous ibutilide versus intravenous amiodarone for post-operative management of atrial fibrillation following coronary artery bypass grafting: a prospective randomized controlled double blinded trial

Background: Increased incidence of post-operative atrial fibrillation (POAF) is responsible for more post-operative complications, length of hospital stay and subsequent higher costs of hospitalization. This study was done to compare the efficacy and safety of ibutilide versus amiodarone for treatment of POAF following coronary artery bypass grafting (CABG).Methods: In this prospective, randomized, double blind controlled study, 60 patients posted for CABG developing POAF, divided randomly into 30 patients each in groups A and group I. Group A received IV amiodarone at 3 mg/kg over 20 minutes and group I received IV ibutilide at 0.01 mg/kg over 10 minutes (weight 60 kg). Patients underwent standard anesthetic technique and monitoring for CABG. All the demographic data, hemodynamic data were recorded in a structured manner.Results: Ibutilide showed significantly faster resolution of AF at 12.47±5.3 versus 22.9±7.68 minutes by amiodarone (p=0.000). Ibutilide was found to have significantly higher incidences of recurrence at 23.3% versus 0% by amiodarone (p=0.0048). Ibutilide showed significantly lesser hypotension 0% versus 26.67% with amiodarone (p=0.002).Conclusions: This study concluded that ibutilide was found to be better suited to treat POAF patients, who underwent CABG; due to its early and efficient resolution and reduced risk of hypotension

(2E)-3-(3,4-Dimeth­oxy­phen­yl)-1-(2,5-dimethyl­thio­phen-3-yl)prop-2-en-1-one

The mol­ecule of the title compound, C17H18O3S, is essentially planar: the phenyl and thio­phene rings form a dihedral angle of 2.79 (10)° and they are inclined to the central propenone unit by 6.20 (15) and 4.78 (15)°, respectively. In the crystal, mol­ecules are connected into dimers via pairs of C—H⋯O inter­actions, generating R 2 2(14) motifs. π–π stacking inter­actions between the thio­phene rings also occur, with a centroid–centroid distance of 3.8062 (12) Å

Special considerations in the management of adult patients with acute leukaemias and myeloid neoplasms in the COVID-19 era: recommendations from a panel of international experts

This article is made available for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.The ongoing COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 is a global public health crisis. Multiple observations indicate poorer post-infection outcomes for patients with cancer than for the general population. Herein, we highlight the challenges in caring for patients with acute leukaemias and myeloid neoplasms amid the COVID-19 pandemic. We summarise key changes related to service allocation, clinical and supportive care, clinical trial participation, and ethical considerations regarding the use of lifesaving measures for these patients. We recognise that these recommendations might be more applicable to high-income countries and might not be generalisable because of regional differences in health-care infrastructure, individual circumstances, and a complex and highly fluid health-care environment. Despite these limitations, we aim to provide a general framework for the care of patients with acute leukaemias and myeloid neoplasms during the COVID-19 pandemic on the basis of recommendations from international experts