Numerical study on the impact of mucus layer and inlet air-temperatures on the particle deposition in a highly idealized mouth-throat model using LES

Particle deposition could decrease the aerodynamic performance and cooling efficiency of turbine vanes and blades. The particle motion in the flow and its temperature are two important factors affecting its deposition. The size of the particle influences both its motion and temperature. In this study, the motion of particles with the sizes from 1 to 20 μm in the first stage of a turbine are firstly numerically simulated with the steady method, then the particle deposition on the vanes and blades are numerically simulated with the unsteady method based on the critical viscosity model. It is discovered that the particle deposition on vanes mainly formed near the leading and trailing edge on the pressure surface, and the deposition area expands slowly to the whole pressure surface with the particle size increasing. For the particle deposition on blades, the deposition area moves from the entire pressure surface toward the tip with the particle size increasing due to the effect of rotation. For vanes, the particle capture efficiency increases with the particle size increasing since Stokes number and temperature of the particle both increase with its size. For blades, the particle capture efficiency increases firstly and then decreases with the particle size increasing.

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Model of thermal buoyancy in cavity-ventilated roof constructions

Journal of Building Physics ◽

10.1177/1744259120984189 ◽

2021 ◽

pp. 174425912098418

Author(s):

Toivo Säwén ◽

Martina Stockhaus ◽

Carl-Eric Hagentoft ◽

Nora Schjøth Bunkholt ◽

Paula Wahlgren

Keyword(s):

Analytical Model ◽

Flow Rate ◽

Numerical Study ◽

Air Flow ◽

Wind Pressure ◽

Air Flow Rate ◽

Test Set ◽

Air Cavity ◽

Thermal Buoyancy ◽

The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

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Impact of Shade and Fogging on High Tunnel Production and Mineral Content of Organically Grown Lettuce, Basil, and Arugula in Georgia

Agriculture ◽

10.3390/agriculture11070625 ◽

2021 ◽

Vol 11 (7) ◽

pp. 625

Author(s):

Savanah Laur ◽

Andre Luiz Biscaia Ribeiro da Silva ◽

Juan Carlos Díaz-Pérez ◽

Timothy Coolong

Keyword(s):

Mineral Content ◽

Planting Date ◽

High Tunnel ◽

Lactuca Sativa L ◽

Air Temperatures ◽

Shade Cloth ◽

High Tunnels ◽

Soil Temperatures ◽

Organically Grown ◽

The Impact

This study evaluated the impact of shade cloth and fogging systems on the microclimate at the plant canopy level and yield of basil (Oscimum basilicum L.), arugula (Eruca vesicaria subsp. Sativa L.), and lettuce (Lactuca sativa L.) planted in mid-September and early October in high tunnels. Fogging systems were installed at canopy level in plots within shaded (30%) and non-shaded high tunnels. Average air temperatures in the shaded high tunnels were 0.9 °C lower than non-shaded high tunnels during the day. Shade cloth significantly reduced soil temperatures during the day and night periods by 1.5 °C and 1.3 °C, respectively, compared to non-shaded treatments. Fogging systems did not have an impact on air temperature, soil temperature, or relative humidity, but did increase canopy leaf wetness. Shade and fogging did not impact the yield of any of the crops grown. Yield was impacted by planting date, with earlier planting result in higher yields of lettuce and basil. Yields for arugula were greater during the second planting date than the first. Planting date and shade cloth interacted to affect the concentrations of macronutrients.

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Cumulative Effects of Particulate Matter Pollution and Meteorological Variables on the Risk of Influenza-Like Illness

Viruses ◽

10.3390/v13040556 ◽

2021 ◽

Vol 13 (4) ◽

pp. 556

Author(s):

Kacper Toczylowski ◽

Magdalena Wietlicka-Piszcz ◽

Magdalena Grabowska ◽

Artur Sulik

Keyword(s):

Particulate Matter ◽

Respiratory Infections ◽

Nonlinear Models ◽

Absolute Humidity ◽

Influenza Viruses ◽

Meteorological Variables ◽

Exponential Relationship ◽

Influenza Like Illness ◽

Air Temperatures ◽

The Impact

The cold season is usually accompanied by an increased incidence of respiratory infections and increased air pollution from combustion sources. As we are facing growing numbers of COVID-19 cases caused by the novel SARS-CoV-2 coronavirus, an understanding of the impact of air pollutants and meteorological variables on the incidence of respiratory infections is crucial. The incidence of influenza-like illness (ILI) can be used as a close proxy for the circulation of influenza viruses. Recently, SARS-CoV-2 has also been detected in patients with ILI. Using distributed lag nonlinear models, we analyzed the association between ILI, meteorological variables and particulate matter concentration in Bialystok, Poland, from 2013–2019. We found an exponential relationship between cumulative PM2.5 pollution and the incidence of ILI, which remained significant after adjusting for air temperatures and a long-term trend. Pollution had the greatest effect during the same week, but the risk of ILI was increased for the four following weeks. The risk of ILI was also increased by low air temperatures, low absolute humidity, and high wind speed. Altogether, our results show that all measures implemented to decrease PM2.5 concentrations would be beneficial to reduce the transmission of SARS-CoV-2 and other respiratory infections.

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Numerical Simulation of the Impact of the Heat Source Position on Melting of a Nano-Enhanced Phase Change Material

Nanomaterials ◽

10.3390/nano11061425 ◽

2021 ◽

Vol 11 (6) ◽

pp. 1425

Author(s):

Tarek Bouzennada ◽

Farid Mechighel ◽

Kaouther Ghachem ◽

Lioua Kolsi

Keyword(s):

Heat Transfer ◽

Phase Change ◽

Phase Change Material ◽

Numerical Study ◽

Melting Rate ◽

Heat Transfer Fluid ◽

Commercial Code ◽

Tube Position ◽

The Impact ◽

Change Material

A 2D-symmetric numerical study of a new design of Nano-Enhanced Phase change material (NEPCM)-filled enclosure is presented in this paper. The enclosure is equipped with an inner tube allowing the circulation of the heat transfer fluid (HTF); n-Octadecane is chosen as phase change material (PCM). Comsol-Multiphysics commercial code was used to solve the governing equations. This study has been performed to examine the heat distribution and melting rate under the influence of the inner-tube position and the concentration of the nanoparticles dispersed in the PCM. The inner tube was located at three different vertical positions and the nanoparticle concentration was varied from 0 to 0.06. The results revealed that both heat transfer/melting rates are improved when the inner tube is located at the bottom region of the enclosure and by increasing the concentration of the nanoparticles. The addition of the nanoparticles enhances the heat transfer due to the considerable increase in conductivity. On the other hand, by placing the tube in the bottom area of the enclosure, the liquid PCM gets a wider space, allowing the intensification of the natural convection.

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OPTIMAL REINSURANCE FROM THE VIEWPOINTS OF BOTH AN INSURER AND A REINSURER UNDER THE CVAR RISK MEASURE AND VAJDA CONDITION

Astin Bulletin ◽

10.1017/asb.2021.9 ◽

2021 ◽

pp. 1-29

Author(s):

Yanhong Chen

Keyword(s):

Loss Function ◽

Value At Risk ◽

Numerical Study ◽

Risk Measure ◽

Convex Combination ◽

Weighting Factor ◽

Loss Functions ◽

Conditional Value At Risk ◽

Optimal Reinsurance ◽

The Impact

ABSTRACT In this paper, we study the optimal reinsurance contracts that minimize the convex combination of the Conditional Value-at-Risk (CVaR) of the insurer’s loss and the reinsurer’s loss over the class of ceded loss functions such that the retained loss function is increasing and the ceded loss function satisfies Vajda condition. Among a general class of reinsurance premium principles that satisfy the properties of risk loading and convex order preserving, the optimal solutions are obtained. Our results show that the optimal ceded loss functions are in the form of five interconnected segments for general reinsurance premium principles, and they can be further simplified to four interconnected segments if more properties are added to reinsurance premium principles. Finally, we derive optimal parameters for the expected value premium principle and give a numerical study to analyze the impact of the weighting factor on the optimal reinsurance.

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A numerical study of the impact perforation of sandwich panels with graded hollow sphere cores

Advances in Mechanical Engineering ◽

10.1177/16878140211009415 ◽

2021 ◽

Vol 13 (4) ◽

pp. 168781402110094

Author(s):

Ibrahim Elnasri ◽

Han Zhao

Keyword(s):

Boundary Conditions ◽

Hollow Sphere ◽

Sandwich Panel ◽

Numerical Study ◽

Sandwich Panels ◽

Hopkinson Bar ◽

Core Density ◽

The Core ◽

The Impact ◽

Force Displacement

In this study, we numerically investigate the impact perforation of sandwich panels made of 0.8 mm 2024-T3 aluminum alloy skin sheets and graded polymeric hollow sphere cores with four different gradient profiles. A suitable numerical model was conducted using the LS-DYNA code, calibrated with an inverse perforation test, instrumented with a Hopkinson bar, and validated using experimental data from the literature. Moreover, the effects of quasi-static loading, landing rates, and boundary conditions on the perforation resistance of the studied graded core sandwich panels were discussed. The simulation results showed that the piercing force–displacement response of the graded core sandwich panels is affected by the core density gradient profiles. Besides, the energy absorption capability can be effectively enhanced by modifying the arrangement of the core layers with unclumping boundary conditions in the graded core sandwich panel, which is rather too hard to achieve with clumping boundary conditions.

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NonlinearL2-Gain Analysis of Hybrid Systems in the Presence of Sliding Modes and Impacts

Mathematical Problems in Engineering ◽

10.1155/2016/9074096 ◽

2016 ◽

Vol 2016 ◽

pp. 1-10 ◽

Cited By ~ 5

Author(s):

T. Osuna ◽

O. E. Montano ◽

Y. Orlov

Keyword(s):

Sliding Mode ◽

Numerical Study ◽

Sufficient Conditions ◽

Disturbance Attenuation ◽

Sliding Modes ◽

Time Dynamics ◽

Attenuation Level ◽

Disturbance Factor ◽

Disturbance Attenuation Level ◽

The Impact

TheL2-gain analysis is extended towards hybrid mechanical systems, operating under unilateral constraints and admitting both sliding modes and collision phenomena. Sufficient conditions for such a system to be internally asymptotically stable and to possessL2-gain less than ana priorigiven disturbance attenuation level are derived in terms of two independent inequalities which are imposed on continuous-time dynamics and on discrete disturbance factor that occurs at the collision time instants. The former inequality may be viewed as the Hamilton-Jacobi inequality for discontinuous vector fields, and it is separately specified beyond and along sliding modes, which occur in the system between collisions. Thus interpreted, the former inequality should impose the desired integral input-to-state stability (iISS) property on the Filippov dynamics between collisions whereas the latter inequality is invoked to ensure that the impact dynamics (when the state trajectory hits the unilateral constraint) are input-to-state stable (ISS). These inequalities, being coupled together, form the constructive procedure, effectiveness of which is supported by the numerical study made for an impacting double integrator, driven by a sliding mode controller. Desired disturbance attenuation level is shown to satisfactorily be achieved under external disturbances during the collision-free phase and in the presence of uncertainties in the transition phase.

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Drops bouncing off macro-textured superhydrophobic surfaces

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.306 ◽

2017 ◽

Vol 824 ◽

pp. 866-885 ◽

Cited By ~ 24

Author(s):

Ali Mazloomi Moqaddam ◽

Shyam S. Chikatamarla ◽

Iliya V. Karlin

Keyword(s):

Contact Time ◽

Numerical Study ◽

Three Dimensional ◽

Superhydrophobic Surfaces ◽

Nonlinear Behaviour ◽

Textured Surfaces ◽

Texture Density ◽

Wide Range ◽

Quantitative Manner ◽

The Impact

Recent experiments with droplets impacting macro-textured superhydrophobic surfaces revealed new regimes of bouncing with a remarkable reduction of the contact time. Here we present a comprehensive numerical study that reveals the physics behind these new bouncing regimes and quantifies the roles played by various external and internal forces. For the first time, accurate three-dimensional simulations involving realistic macro-textured surfaces are performed. After demonstrating that simulations reproduce experiments in a quantitative manner, the study is focused on analysing the flow situations beyond current experiments. We show that the experimentally observed reduction of contact time extends to higher Weber numbers, and analyse the role played by the texture density. Moreover, we report a nonlinear behaviour of the contact time with the increase of the Weber number for imperfectly coated textures, and study the impact on tilted surfaces in a wide range of Weber numbers. Finally, we present novel energy analysis techniques that elaborate and quantify the interplay between the kinetic and surface energy, and the role played by the dissipation for various Weber numbers.

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