scholarly journals Numerical Modeling of the Spread of Cough Saliva Droplets in a Calm Confined Space

Mathematics ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 574
Author(s):  
Sergio A. Chillón ◽  
Ainara Ugarte-Anero ◽  
Iñigo Aramendia ◽  
Unai Fernandez-Gamiz ◽  
Ekaitz Zulueta
Keyword(s):  
Transmission Rate ◽  
Fluid Dynamic ◽  
Global Scale ◽  
Turbulent Dispersion ◽  
Computational Domain ◽  
Inertial Forces ◽  
Transfer Phase ◽  
Confined Space ◽  
Gravitational Forces ◽  
Fully Coupled

The coronavirus disease 2019 (COVID-19) outbreak has altered the lives of everyone on a global scale due to its high transmission rate. In the current work, the droplet dispersion and evaporation originated by a cough at different velocities is studied. A multiphase computational fluid dynamic model based on fully coupled Eulerian–Lagrangian techniques was used. The evaporation, breakup, mass transfer, phase change, and turbulent dispersion forces of droplets were taken into account. A computational domain imitating an elevator that with two individuals inside was modeled. The results showed that all droplets smaller than 150 μm evaporate before 10 s at different heights. Smaller droplets of <30 µm evaporate quickly, and their trajectories are governed by Brownian movements. Instead, the trajectories of medium-sized droplets (30–80 µm) are under the influence of inertial forces, while bigger droplets move according to inertial and gravitational forces. Smaller droplets are located in the top positions, while larger (i.e., heaviest) droplets are located at the bottom.

Three-Dimensional CFD Analysis of Meshing Losses in a Spur Gear Pair

2018 ◽  
Author(s):  
T. Fondelli ◽  
D. Massini ◽  
A. Andreini ◽  
B. Facchini ◽  
F. Leonardi
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Spur Gear ◽  
Computational Domain ◽  
Gear Pair ◽  
Transient Pressure ◽  
Numerical Effort ◽  
Free Environment

The reduction of fluid-dynamic losses in high speed gearing systems is nowadays increasing importance in the design of innovative aircraft propulsion systems, which are particularly focused on improving the propulsive efficiency. Main sources of fluid-dynamic losses in high speed gearing systems are windage losses, inertial losses resulting by impinging oil jets used for jet lubrication and the losses related to the compression and the subsequent expansion of the fluid trapped between gears teeth. The numerical study of the latter is particularly challenging since it faces high speed multiphase flows interacting with moving surfaces, but it paramount for improving knowledge of the fluid behavior in such regions. The current work aims to analyze trapping losses in a gear pair by means of three-dimensional CFD simulations. In order to reduce the numerical effort, an approach for restricting computational domain was defined, thus only a portion of the gear pair geometry was discretized. Transient calculations of a gear pair rotating in an oil-free environment were performed, in the context of conventional eddy viscosity models. Results were compared with experimental data from the open literature in terms of transient pressure within a tooth space, achieving a good agreement. Finally, a strategy for meshing losses calculation was developed and results as a function of rotational speed were discussed.

Study of Air Inclusion in Lubrication System of CVT Gearbox Transmission With Biphasic CFD Simulation

2016 ◽  
Author(s):  
Cristian Ferrari ◽  
Pietro Marani
Keyword(s):  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Critical Conditions ◽  
Positive Pressure ◽  
Computational Domain ◽  
Lubrication System ◽  
Operation Condition ◽  
Dynamic Simulations ◽  
Lubrication Performance ◽  
Lumped Element Model

The focus of this paper is the biphasic phenomena that occurs in a lubrication system of a CVT gearbox transmission of an agricultural tractor, in particular a Method of Analysis is outlined with the aim of mapping and assessing the behavior of the lubrication circuit. The study of the lubrication in gearboxes is an important issue in the design of off-road machines because their reliability depends mostly on the lubrication performance, as well as the machine’s lifetime and overall energy efficiency of the transmission is strongly dependent on the lubrication system behavior. In fact the role of the lubrication system is twofold: firstly to remove the heat generated in the highly loaded rolling bearings and the gears found in the power and accessory gearboxes via heat exchangers; secondly to lubricate these parts. The trend in the development of gearbox transmissions has been towards lower consumption and higher power transmitted, consequently it is necessary to conceive more effective and efficient lubrication systems. Nonetheless the lubrication problem often relies on a trial and error approach and most available scientific literature is based on lumped element model dynamic simulation or one phase thermo-fluid dynamic simulations, overlooking the effects linked to cavitation and air inclusion. One important phenomenon in lubrication systems is that of air suction. This can be seen in particular at high rotational speeds of shafts when the centrifugal force causes a positive pressure drop between inner lubrication pipes and outer radial conduits. In this case the air occupies part of the lubrication conduits, and since the domain is shared by the outflowing liquid phase and the air included, the monophase CFD simulation fails to predict the correct lubrication flow. If this effect is not carefully considered it could cause a lubrication unbalance among the various parts of the gearbox, creating a risk of transmission damage. In this paper the methodology will be presented step by step until in final a complete map of operation condition is created. A preliminary analysis of the circuitry is an essential phase of the project since the tractor’s transmission is an extremely complex assembly composed by hundreds of components therefore the lubrication circuit appears as a large net of moving hydraulic connections and consumers. From this analysis a computational domain is obtained and appropriately meshed. After the pivotal choice of the proper turbulence model and boundary conditions, various runs at different rotating speeds corresponding to the different operating ranges will be performed. The result will be contextualized by commenting on the fluid dynamics phenomena involved and the influence parameters on flow rate distribution, finally evaluating the performances of the lubrication circuit, and in particular highlighting the most critical conditions in terms of speed condition and locating the most critical gearbox parts.

CFD CHARACTERIZATION OF FLOW PATTERN AROUND ENDOTHELIAL CELL IN DENGUE INFECTION WITH PLASMA LEAKAGE

2015 ◽  
Vol 76 (7) ◽  
Author(s):  
Nur Kaliwantoro ◽  
Marsetyawan HNE Soesatyo ◽  
Indarto Indarto ◽  
Mohammad Juffrie ◽  
Rini Dharmastiti ◽  
...  
Keyword(s):  
Shear Stress ◽  
Endothelial Cell ◽  
Dengue Virus ◽  
Fluid Dynamic ◽  
Dengue Infection ◽  
Leading Edge ◽  
Cell Junction ◽  
Computational Domain ◽  
Permeable Membrane ◽  
Plasma Leakage

Plasma leakage is the pathological hall mark in dengue infection and may cause fatal condition to the patients. In this paper, the CFD (computational fluid dynamic) model is adopted to characterize the flow on the endothelial cells surface with plasma leakage based on in vitro experiments of HUVEC (human umbilical vein endothelial cell) culture on the permeable membrane. The computational domain used is a simplified model of single cell. At the leading edge of the domain and among the membranes, the gaps are modeled as a representation of cell-cell junction breakdown caused by dengue virus infection.  The result shows that at the leading edge , the fluid starts to move more quickly and increases to the maximum value at the middle of the cell and then drops to zero at the trailing edge. From the physical point of view, this result describes that there is a variation of the values of the wall shear stress due to the velocity gradient. These results can be considered as a first step to develop the ways of the prevention of the dengue infection through manipulation the shear stress to reduce the potency of dengue virus to attach the cell surface.  

Fully-Coupled Turbojet Engine CFD Simulations and Cycle Analyses Along the Equilibrium Running Line

2020 ◽  
Author(s):  
Alejandro Briones ◽  
Andrew W Caswell ◽  
Brent Rankin
Keyword(s):  
Flow Rate ◽  
Fluid Dynamic ◽  
Thermodynamic Cycle ◽  
Angular Speed ◽  
Small Scale ◽  
Cfd Simulations ◽  
Fuel Flow ◽  
Turbojet Engine ◽  
Design Cycle ◽  
Fully Coupled

Abstract This work presents fully-coupled computational fluid dynamic (CFD) simulations and thermodynamic cycle analyses of a small-scale turbojet engine at several conditions along the equilibrium running line. The CFD simulations use a single mesh for the entire engine, from the intake to the exhaust, allowing information to travel in all directions. The CFD simulations are performed along the equilibrium running line by using the iterative Secant method to compute the fuel flow rate required to match the compressor and turbine power. The freestream pressure and temperature and shaft angular speed are the only inputs needed for the CFD simulations. To evaluate the consistency of the CFD results with thermodynamic cycle results, outputs from the CFD simulations are prescribed as inputs to the cycle model. This approach enables on-design and off-design cycle calculations to be performed without requiring turbomachinery performance maps. In contrast, traditional off-design cycle analyses require either scaling, calculating, or measuring compressor and turbine maps with boundary condition assumptions. In addition, the CFD simulations and the cycle analyses are compared with measurements of the turbojet engine. The CFD simulations, thermodynamic cycle analyses, and measurements agree in terms of total temperature and pressure at the diffuser-combustor interface, air and fuel mass flow rate, equivalence ratio, and thrust. The developed methods to perform CFD simulations from the intake to the exhaust of the turbojet engine are expected to be useful for guiding the design and development of future small-scale gas turbine engines.

Cyclic Breathing Simulations in Large-Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
D. Keith Walters ◽  
Greg W. Burgreen ◽  
Robert L. Hester ◽  
David S. Thompson ◽  
David M. Lavallee ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Mass Flow ◽  
Flow Rate ◽  
Large Scale ◽  
Whole Body ◽  
Patient Specific ◽  
Computational Domain ◽  
Scale Models ◽  
Fully Coupled ◽  
Conducting Zone

Computational fluid dynamics (CFD) simulations were performed using large-scale models of the human lung airway and unsteady periodic breathing conditions. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to the 16th generation) obtained from a stochastically generated airway tree with statistically realistic morphological characteristics. A reduced-geometry airway model was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to the 16th generation. The inlet and outlet flow boundaries corresponded to the oral opening, the physical inlet/outlet boundaries at the terminal bronchioles, and the unresolved airway boundaries created from the truncation procedure. The total flow rate was specified according to the expected ventilation pattern for a healthy adult male, which was supplied by the whole-body modeling software HumMod. The unsteady mass flow distribution at the distal boundaries was prescribed based on a preliminary steady-state simulation with an applied flow rate equal to the average flow rate during the inhalation phase of the breathing cycle. In contrast to existing studies, this approach allows fully coupled simulation of the entire conducting zone, with no need to specify distal mass flow or pressure boundary conditions a priori, and without the use of impedance or one-dimensional (1D) flow models downstream of the truncated boundaries. The results show that: (1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; (2) the predicted alveolar pressure is in good agreement with correlated experimental data; and (3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

scholarly journals On the generation of the mean velocity profile for turbulent boundary layers with pressure gradient under equilibrium conditions

2012 ◽  
Vol 116 (1180) ◽  
pp. 569-598 ◽  
Author(s):  
A. Rona ◽  
M. Monti ◽  
C. Airiau
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Pressure Gradient ◽  
Fluid Dynamic ◽  
Predictive Ability ◽  
Adverse Pressure Gradient ◽  
Computational Domain ◽  
Mean Velocity ◽  
Number Range

AbstractThe generation of a fully turbulent boundary layer profile is investigated using analytical and numerical methods over the Reynolds number range 422 ≤ Reθ≤ 31,000. The numerical method uses a new mixing length blending function. The predictions are validated against reference wind tunnel measurements under zero streamwise pressure gradient. The methods are then tested for low and moderate adverse pressure gradients. Comparison against experiment and DNS data show a good predictive ability under zero pressure gradient and moderate adverse pressure gradient, with both methods providing a complete velocity profile through the viscous sub-layer down to the wall. These methods are useful computational fluid dynamic tools for generating an equilibrium thick turbulent boundary layer at the computational domain inflow.

Thermal and Fluid Dynamic Analysis on Impinging Jet for Aircraft Anti-Icing

2010 ◽  
Author(s):  
Assunta Andreozzi ◽  
Fabio Lucibello ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
Mario Roma
Keyword(s):  
Fluid Dynamic ◽  
Three Dimensional ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Wing Surface ◽  
Temperature Fields ◽  
Ice Formation ◽  
Computational Domain ◽  
System A ◽  
Wing Profile

Ice formation on airplane wing profile is a very dangerous condition because of the change in the profile aerodynamic, so it’s necessary to avoid ice formation on the wings. The hardest condition ice formation are at altitudes between 10.000 and 15.000 ft and at temperature between 0° C and −15° C, because they are particularly suitable for ice formation. In this paper an anti-icing system based on hot air impinging jets on internal wing surface is analyzed in order to check the efficiency of the system. A numerical model is given in order to evaluate the thermal and fluid dynamic behaviors of the impinging jet inside the wing panel. A wing profile with an angle of attack of 4.50° is taken into account with a free stream temperature of 258 K. A piccolo tube with a diameter of 1.00 inch and air temperature of 523 K and at variable distance from the wall of the wing profile, is considered for anti-icing system. A structured mesh is used in the discretization of the computational domain for the two-dimensional and three-dimensional case. A steady state solution with k-ε RNG turbulent model has been found. Numerical simulations of a two and a three dimensional model of an aircraft wing has been carried out taking into account the external convective exchange by means of an average coefficient on the external surface and thermo-fluid dynamic field inside the wing due to the anti-icing system. The analysis is performed by means of the FLUENT code in order to find the optimal geometrical configuration to avoid the ice formation on the external wing surface. Results are presented in terms of temperature fields and wall temperature and air velocity profiles along the wing surfaces.

scholarly journals Decline in global transmission rates of COVID-19

2020 ◽  
Author(s):  
Ethan Romero-Severson ◽  
Nick Hengartner ◽  
Grant Meadors ◽  
Ruian Ke
Keyword(s):  
Particle Filtering ◽  
Transmission Rate ◽  
Global Scale ◽  
Initial Growth ◽  
Social Distancing ◽  
Transmission Rates ◽  
Case Count ◽  
Slow Decline ◽  
Detection Probabilities ◽  
Variable Transmission

AbstractOur method uses a hybrid deterministic and stochastic formalism that allows for time variable transmission rates and detection probabilities. The model was fit using iterated particle filtering to case count and death count time series from 51 countries. We found evidence for a declining transmission rate in 42 of the 51 examined countries. Of those 42 countries 34 have significant evidence for subcritical transmission rates, although the decline in new cases are relatively slow compared to the initial growth rates. This suggests that global scale social distancing efforts to slow the spread of COVID-19 are effective although they need to be strengthened in many regions and maintained in others to avoid further resurgence of COVID-19. The slow decline also suggests alternative strategies to control the virus are needed before social distancing efforts are partially relaxed.

Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner

2019 ◽  
Author(s):  
Heena Panchasara ◽  
Pankaj S. Kolhe ◽  
Ajay K. Agrawal
Keyword(s):  
Gas Turbine ◽  
Axial Velocity ◽  
Alternative Fuels ◽  
Dynamic Models ◽  
Fuel Injection ◽  
Fluid Dynamic ◽  
Droplet Diameter ◽  
Distribution Functions ◽  
Turbulent Dispersion ◽  
Radial Profiles

Abstract Fuel injection plays an important role in liquid fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel-air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio (ALR) by mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter are presented to show the effect of fuel preheating. Joint Probability Density Functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.

scholarly journals Computational fluid dynamic modelling of supersonic ejectors: comparison between 2D and 3D modelling

2021 ◽  
Vol 2116 (1) ◽  
pp. 012091
Author(s):  
Giorgio Besagni ◽  
Lorenzo Croci ◽  
Nicolò Cristiani ◽  
Fabio Inzoli ◽  
Gaël Raymond Guédon
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
A Priori ◽  
Dynamic Modelling ◽  
Global Scale ◽  
Entrainment Ratio ◽  
Local Flow ◽  
Supersonic Ejector ◽  
Precise Knowledge ◽  
Flow Phenomena

Abstract It is known that the global performances of ejector-based systems (viz., at the “global-scale”) depend on the local flow properties within the ejector (viz., at the “local-scale”). For this reason, reliable computational fluid-dynamics (CFD) approaches, to obtain a precise and an a-priori knowledge of the local flow phenomena, are of fundamental importance to support the deployment of innovative ejector-based systems. This communication contributes to the existing discussion by presenting a numerical study of the turbulent compressible flow in a supersonic ejector. In particular, this communication focuses on a precise knowledge gap: the comparison between 2D and 3D modelling approaches as well as density-based and pressure-based solvers. The different approaches have been compared and validated against literature data consisting in entrainment ratio and wall static pressure measurements. In conclusion, this paper is intended to provide guidelines for researchers dealing with the numerical simulation of ejectors.

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