Multiple-relaxation-time lattice Boltzmann simulation of natural convection flow in a partitioned cavity using GPU computing

© 2019 Author(s). In this paper, we demonstrated the implementation of General Purpose Graphics Processing Unit (GPGPU) programming in Compute Unified Device Architecture (CUDA) C for the simulation of natural convection flow in a side-heated three-dimensional (3D) rectangular cavity with a partition. In the present lattice Boltzmann method (LBM) D3Q19 multiple-relaxation-time (MRT) and D3Q6 single relaxation-time (SRT) model are implemented for the simulation of fluid flow and temperature phenomena, respectively. The parallel code is validated with the benchmark problem of a side heated cubic cavity. The results are presented by the temperature distribution in terms of isotherms, local and average Nusselt number and 3D view of iso-surface for the different Rayleigh number (Ra) and the Prandtl number fixed at Pr = 0.71. It is also observed that the present parallel implementation of the MRT-lattice Boltzmann simulation in GPU has a substantial computational effciency rather than the sequential programming in central processing units (CPU)

Aerosol particle transport and deposition in a CT-scan based mouth-throat model

© 2019 Author(s). A precise understanding of the aerosol particle transport and deposition (TD) in the realistic mouth-throat model is important for the respiratory health risk assessment and effective delivery of the aerosol medicine to the targeted positions of the lung. A wide range of studies have developed the particle TD framework for both idealized and non-idealized extra-thoracic airways. However, all of the existing in silico and experimental model reports a significant amount of aerosol particles are deposit at the extra-thoracic airways and the existing drug delivery device can deliver only 12 percent of the aerosol drug to the targeted position of the lung. This study aims to increase the efficiency of the targeted drug delivery by developing a realistic particle transport model for CT-Scan based mouth-throat replica. A 3-D realistic mouth-throat model is developed from the CT-Scan DiCom images of a healthy adult cast. High-Quality computational cells are generated for the replica model and the proper grid refinement test has been performed. ANSYS Fluent (19.1) solver is used for the particle TD computation. Tecplot and MATLAB software are used for the post-processing purpose. The numerical results report that the breathing pattern and particle diameter influences the overall particle TD in the mouth-throat model. The numerical results also depict different deposition hot spots for the mouth-throat model, which will eventually help to design a better drug delivery device. The numerical results reported that only 13.67 percent of the 10-μm diameter particles are deposited at the mouth-throat model at 15 lpm flow rate and which indicate that the remaining particles will move to the beyond airways. The present results along with more case studies will develop the understanding of the realistic particle deposition in the extrathoracic airways

Transient free convection and heat transfer in a partitioned attic-shaped space under diurnal thermal forcing

One primordial consideration in residential ventilation standards is the comfort of provided to people living in those habitations. This is highly dependent on the thermal and fluid flow conditions, the space geometry and so on. Efficient designs may reduce the energy usage, making the buildings more sustainable over a longer period of time. This study aims to investigate the impact of whole day thermal conditions on the fluid flow structure and heat transfer phenomena, mainly natural convection, inside a partitioned attic-shaped configuration. The Finite Volume Method is applied to solve the governing equations. Sinusoidal thermal boundary condition is applied on the sloping walls to illustrate the characteristics of primary flow through daily cycles. A highly thermal conductive partition was placed vertically at the middle of the cavity. Note that through the partition, only heat could freely transfer between two fluid zones. Results show that, during day time, a stratified fluid flow structure is obtained, which originates from the prevailing conduction heat transfer mechanism, while, for the night-time it changed into a strong convection mechanism which significantly affects the flow structure. These results are particularly important for understanding the fluid dynamics inside the attic shaped building and also designing new residential building

Lattice boltzmann simulation of magnetic field effect on electrically conducting fluid at inclined angles in rayleigh-bénard convection

The magneto-hydrodynamics (MHD) effect is studied at different inclined angles in Rayleigh-Bénard (RB) convection inside a rectangular enclosure using the lattice Boltzmann method (LBM). The enclosure is filled with electrically conducting fluids of different characteristics. These characteristics are definedbyPrandtlnumber,Pr. The considered Pr values for this study are 10 and 70. The influence of other dimensionless parameters Rayleigh numbers Ra ¼ 103; 104; 105; 106 and Hartmann numbers Ha = 0, 10, 25, 50, 100, on fluid flow and heat transfer, are also investigated considering different inclined angles φ of magnetic field by analyzing computed local Nusselt numbers and average Nusselt numbers. The results of the study show the undoubted prediction capability of LBM for the current problem. The simulated results demonstrate that the augmentation in heat transfer is directly related to Ra values, but it is opposite while observing the characteristics of Ha values. However, it is also found that φ has a significant impact on heat transfer for different fluids. Besides, isotherms are found to be always parallel to the horizontal axis at Ra ¼ 103 as conduction over-comes the convection in the heat transfer, but this behaviour is not seen at Ra ¼ 104 when Ha > 25. Furthermore,at Ra ¼ 106, oscillatory instability appears but LBM is still able to provide a complete map of this predicted beha-vior. An appropriate validation with previous numerical studies demonstrates the accuracy of the present approach

Large-Eddy Simulation of Airflow and Pollutant Dispersion in a Model Street Canyon Intersection of Dhaka City

The atmospheric flow and dispersion of traffic exhaust were numerically studied in this work while considering a model street canyon intersection of a city. The finite volume method (FVM)-based large-eddy simulation (LES) technique in line with ANSYS Fluent have been used for flow and pollutant dispersion modelling through the consideration of the atmospheric boundary layer (ABL). Hexahedral elements are considered for computational domain discretization in order to numerically solve problems using FVM-LES. The turbulence parameters were superimposed through a spectral synthesizer in the existing LES model through ANSYS Fluent as part of ’damage control’ due to the unsteady k−ϵ simulation. Initially, the code is validated with an experimental study of an urban street canyon where the width and height ratio is in unity. After validation, a model urban street canyon intersection was investigated in this work. The model shows a high pollutant concentration in the intersecting corner areas of the buildings. Additionally, the study of this model intersection shows a high level of pollutant concentration at the leeward wall of downwind building in the case of increased height of an upwind building. Most importantly, it was realized from the street intersection design that three-dimensional interconnection between the dominating canyon vortices and roof level flow plays a pivotal role in pollutant concentration level on the windward walls. The three-dimensional extent of corner eddies and their interconnections with dominating vortices were found to be extremely important as they facilitate enhanced ventilation. Corner eddies only form for the streets towards the freeway and not for the streets towards the intersection. The results and key findings of this work offer qualitative and quantitative data for the estimation, planning, and implementation of exposure mitigation in an urban environment

Translation without eIF2 Promoted by Poliovirus 2A Protease

Poliovirus RNA utilizes eIF2 for the initiation of translation in cell free systems. Remarkably, we now describe that poliovirus translation takes place at late times of infection when eIF2 is inactivated by phosphorylation. By contrast, translation directed by poliovirus RNA is blocked when eIF2 is inactivated at earlier times. Thus, poliovirus RNA translation exhibits a dual mechanism for the initiation of protein synthesis as regards to the requirement for eIF2. Analysis of individual poliovirus non-structural proteins indicates that the presence of 2Apro alone is sufficient to provide eIF2 independence for IRES-driven translation. This effect is not observed with a 2Apro variant unable to cleave eIF4G. The level of 2Apro synthesized in culture cells is crucial for obtaining eIF2 independence. Expression of the N-or C-terminus fragments of eIF4G did not stimulate IRES-driven translation, nor provide eIF2 independence, consistent with the idea that the presence of 2Apro at high concentrations is necessary. The finding that 2Apro provides eIF2-independent translation opens a new and unsuspected area of research in the field of picornavirus protein synthesis