Airflow Model Research Articles

Derivation of High-Resolution Meteorological Parameters for Use in Airport Wind Shear Now-Casting Applications

Methods for now-casting adverse weather conditions with the potential to cause disruption to aircraft landings often make use of real-time measurements at high temporal resolution. This paper describes processing methodologies developed to derive meteorological parameters from such measurements recorded in the vicinity of Hong Kong International Airport, specifically a radiometer in King’s Park, a wind profiler and surface anemometer on Cheung Chau Island and weather buoys in the Pearl River estuary. These parameters are suitable for use as input to a now-casting application of the computationally efficient airflow model, FLOWSTAR, which has previously been shown to predict mountain waves generated by flow over Lantau Island to the southeast of the airport. Radiosonde data from King’s Park have been used to test the radiometer processing method; the novel approach of using minimum and maximum potential temperature deviations from a series of height-dependent linear profiles to derive radiometer inversion layer parameters generates data that compares well with values derived from corresponding radiosonde profiles. Mountain wave strength depends on the magnitude of wind speed in the inversion layer; wind profiler data can be used to estimate typical and maximum wind speeds and associated wind directions using estimates of inversion layer depth derived from the radiometer data. With estimates of surface sensible heat flux appropriate for the airport’s coastal location calculated using a marine boundary layer scheme, a dataset of meteorological parameters at 20-min resolution has been derived for input into the FLOWSTAR model. The combination of automated meteorological data processing methods and flow field modelling has the potential to form part of a now-casting system for determining strong wind shear conditions at the airport.

Modeling of supply airflow from slot line diffuser on ceiling for CFD of thermal environment in perimeter zone

The slot line diffuser is widely used in Japan near the perimeter windows because of its blocking effect on convective heat transfer. However, research on this diffuser has mainly focused on the effects of the turbulence model on CFD simulations and longitudinal airflow distribution, while studies on its detailed outlet characteristics in three-dimensional have been limited. In order to obtain and summarize this diffuser's outlet characteristics more accurately, this paper set a slot line diffuser with an adjustable outlet area in free space. The detailed velocity and turbulence statistics distribution on the diffuser's outlet surface were obtained by a hot-wire anemometer, and the diffuser's airflow distribution in the free space was measured by an ultrasonic anemometer. Then the outlet characteristics of this diffuser were summarized using these measured data in order to make a detailed supply airflow model. At the same time, the difference of the airflow of full-size supply and that of half-size supply is characterized. Moreover, a detailed CFD simulation of the diffuser's outlet airflow was performed using the characteristics model to define the boundary conditions. The detailed CFD result with outlet characteristics model were validated by comparing with experimental data. Additionally, the prescribed velocity (P.V.) method and simple boundary simulation were also attempted to reproduce the diffuser's outlet airflow, and compared with the experiment and detailed CFD results. This study clarified this diffuser's outlet characteristics in three-dimensional, and it is considered that the outlet characteristics model can help improve the simulation accuracy of the kind of diffuser.

Evaluation of fast fluid dynamics with different turbulence models for predicting outdoor airflow and pollutant dispersion

Fast fluid dynamics (FFD) could provide informative and efficient airflow and concentration simulation. The commonly used turbulence model in FFD was Re-Normalization Group (RNG) k-ε turbulence model which solved two transport equations to obtain eddy viscosity. To reduce this part of time and further improve computing speed, this investigation implemented no turbulence model, Smagorinsky model and dynamic Smagorinsky model which calculated eddy viscosity without solving equation in FFD in an open-source program, OpenFOAM. By simulating several outdoor cases of varying complexity and comparing with experiment and CFD, this study assessed the accuracy and computing efficiency of FFD with four turbulence models. Compared with CFD, FFD greatly improved the computing speed without reducing accuracy. The simulation of FFD without turbulence model was fast but inaccurate. FFD with Smagorinsky model increased the computing speed while ensuring the same accuracy as RNG k-ε turbulence model. FFD with dynamic Smagorinsky model provided accurate results with high efficiency. Computation errors arose mainly from inaccurate prediction of turbulence dispersion. The computing cost was associated with the number of transport equations and calculation method of model coefficient. This investigation recommended the use of FFD with dynamic Smagorinsky model for outdoor airflow and pollutant dispersion studies.

Generalizability evaluation of k-ε models calibrated by using ensemble Kalman filtering for urban airflow and airborne contaminant dispersion

The low accuracy of Reynolds-averaged Navier-Stokes (RANS) modeling of urban airflow and airborne pollutant dispersion is attributed to model flaws and uncertainty contributed by closure coefficients. Previous studies have attempted to improve the performance of RANS modeling by ad hoc calibration of the turbulence model coefficients specifically for urban problems. However, these models failed to accurately reproduce the key features like the reattachment lengths. In addition, there was a lack of generalizability evaluations of the calibrated models. To optimize the accuracy and generalizability of the turbulence model, this study considered the effects of optimization objectives and model formulations. Six k-ε based turbulence models calibrated using the ensemble Kalman filtering (EnKF) approach were compared. A wind tunnel experiment consisting of key features of the airflow around a single-building model was conducted to provide the training data. The proposed optimization objective prioritizing the reproduction of the reattachment lengths in the calibrations enabled the calibrated models to capture the key features of the airflow with better accuracy. The six turbulence models before and after the calibrations were compared for a single-building test case and a building-array test case with respect to the reattachment lengths, velocity, turbulence kinetic energy, and airborne contaminant concentration. The calibrated models with different formulations exhibit distinctive generalizability. The calibrated Murakami-Mochida-Kondo k-ε model (MMK) exhibited strong potential for generalizability to single-building problems. However, the generalization from the single-building isolated roughness flow regime to the street canyon skimming flow regime is limited.

CFD modeling of air flow, humidity, CO2 and NH3 distributions in a caged laying hen house with tunnel ventilation system

In poultry houses, the ventilation system should provide a favorable standard living environment for hens. In addition to uniform distribution of velocity and temperature, concentration of gaseous CO2 and NH3 pollutants and the humidity distribution, which affect the air quality in the poultry house, are of prime importance. In previous numerical studies on caged laying hen houses with tunnel ventilation system, these five concerns have not been examined concurrently. To address all of these issues, in this numerical study a previously studied laying hen house with 4 rows of cages equipped with tunnel ventilation system using evaporative cooling pads has been considered in summer. 3D numerical simulations indicated the deficiency of previous models for provision of proper temperature and velocity distributions also ignoring investigation of humidity and concentration of gaseous pollutants. Thus three new models were proposed, in which the position and number of evaporative cooling pads and exhaust fans and their capacity were altered. Evaluation showed that the second new model, in which 15 fans are on the east wall and three evaporative cooling pads are on the west wall, provides the best performance. In this model, the speed at the levels of the birds is 2.5 m.s-1 and the maximum temperature is 308 K. Also, the relative humidity is between 60 and 75%, which is 10% lower than that of the original model of previous study and CO2 and NH3 concentrations are within the tolerable range everywhere. The CFD techniques utilized in this study may be extended to simulate other poultry houses with any ventilation system such as tunnel, mixed or any other inlet/outlet arrangements, however for the results to be reliable simulation should involve air flow, thermal and humidity fields as well as CO2 and NH3 concentrations.

Simplified model of airflow and heat transfer in a pallet of food product generating heat

AbstractDuring storage, pallets of food product generating heat (e.g., cheese, fruit, and vegetable) are exposed to low velocity ventilation. In addition, the boxes have often little perforation. Therefore airflow is weak inside the boxes located downstream of the pallet; and if the product generates heat, its temperature can rise above the recommended one. Computational fluid dynamics modeling can predict these phenomena but needs an expertise of numerical fluid flow, a detailed description of product and packaging and leads to expensive computational costs. A simplified model is here developed based on a hydraulic network analogy. Given the vent holes areas of the boxes and the heat generation, it predicts the global air flow (flow through the box faces) and the product temperature. The predictions are in good agreement with experimental data. The software (Matlab executable) is easy to use and needs only some seconds to compute. It can be used to predict temperature evolution along a cold chain and to improve packaging and logistic operating conditions.Practical applicationsBased on a on a hydraulic network analogy, a simplified zonal model of airflow and heat transfer in a pallet of food generating heat is built with the Matlab software. It takes into account the vent holes areas of the boxes and the heat generation, and allows predicting the distribution of air fluxes through the box faces and the product temperature. The major advantage of this model is that it is easy to use and needs only some seconds to compute. Therefore, it can be easily used in industrial field.

Intensification of heat and mass transfer of the gas channel of the multi-temperature condensation filter

The principle of operation and features of hydrodynamics and heat-mass transfer in the working channel of a multi-temperature condensation filter for gas purification are described. Promising methods of gas flow purification using porous surfaces are described. The modeling and comparison of the laminar air flow in channels of various shapes: in a flat channel, in a channel with webs and in a spiral channel are performed. An analysis of their effectiveness is carried out.

Hydrodynamics and Heat Transfer Analysis of Airflow in a Sinusoidally Curved Channel

For heat transfer enhancement in heat exchangers, different types of channels are often tested. The performance of heat exchangers can be made better by considering geometry composed of sinusoidally curved walls. This research studies the modeling and simulation of airflow through a units long sinusoidally curved wavy channel. For the purpose, two-dimensional Navier Stokes equations along with heat equations are under consideration. To simulate the fluid flow problem, the finite element-based software COMSOL Multiphysics is used. The parametric study for Reynolds number from to and the period of vibration <i>P</i> from to are observed. The surface plots, streamline patterns, contours, and graphs are presented for the velocity field magnitude, temperature, and pressure against the Reynolds number as well as period of vibration. The results are compared with various literature. It is found that due to the creation of periodic contraction regions the velocity magnitude of the flow is continuously increasing with the increase of Reynolds number, on the contrary the pressure is decreasing from inlet to outlet of the channel. Also, a periodic variation in the pressure distribution along the vibrating boundaries has been found with an average increase of for the high Reynolds number. A novel work was done by expressing the rotation rate per second in terms of local Reynolds number for the recirculating regions found due to the periodic oscillation of the boundaries. The average temperature near the outlet where a fixed temperature is imposed initially is decreasing with an increase in Reynolds number. The convection process is weakened due to an increase of periodic vibration of boundaries.

Підвищення продуктивності процесу лиття шляхом регулювання теплового режиму кокіля на основі комп’ютерного дослідження потоку повітря в каналах стержня

The most common technology for the manufacture of aluminum parts and blanks is casting in a chill mold. To determine ways to improve casting technology, it is necessary to analyze the possibility of changing the parameters that affect the reduction of production costs (reduction of energy consumption, material consumption, increase productivity) and improve the quality of casting. The thermal regime of the metal form determines the productivity of the process, the duration of curing of the casting, its quality, durability of the chill mold. The analysis of the work of the chill mold for the manufacture of castings Pump Housing showed that when the forms are filled, the most heated new portions of metal meet on their way to the central core. That is, when pouring the mold, the central core is heated the most, especially in the lower part. This circumstance hinders the process of directed curing and can lead to shrinkage defects. In addition, the higher the temperature of the mold, the slower the casting will crystallize and the worse its structure and mechanical properties will be. Based on the analysis of structures and methods of cooling molds, the method of controlled cooling of the central core by air is substantiated. A new design of the core has been developed, which provides adjustable air cooling of the chill mold by connecting the central core through a valve to the pneumatic system of the shop. 3D-models of details and assembly drawings of the central core of a new design are developed. A computer study of the air flow in the core channels in SolidWorks Flow Simulation was performed. The results of parametric modeling of air flow in the channels of the Central core showed the maximum air flow rate during cooling 0.371 kg / s, the heat content of air when cooled 25081 J / s. Evaluation of the cooling efficiency of the developed chill mold design showed that when using air cooling of the central core with cooling air at its maximum consumption, 41% of heat is removed. Thus, the developed design of the cooled central core allows to increase the productivity of the casting process, improve the quality of casting by improving the structure and mechanical properties of the casting, as well as increase the life of the chill mold. But the obtained research results are of a recommendatory nature and require practical verification in the production environment. In addition, the simulation did not take into account the change in core temperature due to its heat exchange with the melt. Given all this, there is a need for further study of the effect of regulated air cooling on the thermal regime of the chill mold.

Hopper Bottom Semi-Trailer Modified for In-Shell Peanut Drying: Design, Fabrication, and Performance Testing

HighlightsComputational fluid dynamics modeling of airflow through the peanut load improved the design process.Peanuts dried using the modified hopper bottom semi-trailer passed inspection at 9.1% moisture content in preliminary tests.Final moisture gradient in the modified hopper bottom semi-trailer consisted of even layers from front-to-back with moisture increasing with depth.Current inspection probe sampling pattern biases inspection moisture measurements lower by not sampling the hopper bottom.Abstract. Hopper bottom semi-trailers (HBST) modified to dry loads of in-shell peanuts would provide several advantages to peanut producers and peanut processing facility operators. Producers who have HBST for transporting grain would have an additional use for their HBST and would reduce harvest delays during peak harvest times when trailer availability is limited from peanut processors. Additionally, smaller processing facilities would gain the economic advantages of semi-trailers without the investment in hydraulic lifts to unload peanut drying van semi-trailers. Before this study, no HBST had been modified to add peanut drying functionality. The objectives of this study were to design, fabricate, and test the performance of drying modifications to a HBST. After review of the functional components needed to dry peanuts and existing structural constrains of the HBST, the components fabricated were an air inlet connection, an enclosed transition space, an air plenum vent, and air exhaust vents on the undersides of the hopper tubs. The number, size, and location of the air exhaust vents were determined using a computational fluid dynamic model. Three test loads of peanuts were dried in the modified HBST during the 2020 peanut harvest season. Measurements were taken at intervals throughout the peanut drying process to assess drying and to monitor air temperature and relative humidity. Results of a test load indicated that the moisture content decreased from 12.9% wet basis (w.b.) to 12.0% w.b. after 8.5 h of drying. Average moisture content was reduced to 11.1% w.b. following an additional 8.6 h without the dryer operating. The sample load official grade moisture content was 9.1% w.b after the rest period. The most important finding was that a moisture gradient persisted in the loads of peanuts after active drying and rest period. The peanuts located at the top of the load had a moisture content of 9% w.b. while those with the highest moisture content of 14% w.b. were at the bottom of the load. The official inspection sampling procedure did not detect the moisture content differences in the test loads. The finding of a persistent moisture gradient will require more investigation and modification of the HBST. Keywords: Computational Fluid Dynamics, CFD, Design, Drying, Hopper-bottom semi-trailer, Moisture distribution, Moisture gradient, Peanuts, Retrofit.

Experimental study on the evolution characteristics of near-surface airflow in limited waters

气流作为湖泊、湿地等有限水域的主要驱动力之一，其演化特征是研究水-气间能量与物质传递的基础，决定了水域水环境与水生态格局，具有重要研究意义.采用室内风洞水槽，通过设置不同试验风速，研究近水面气流与风速和吹程的响应关系与演化特征，并将光滑壁面条件下的气流特征作为试验对照组，分析时间域内风速垂向分布形式、摩阻风速、特征粗糙度等变化规律，剖析频率域内风速的主频变化与波致气流边界层厚度等参数的分布特征.结果表明：近水面时均风速符合对数分布，摩阻风速与特征粗糙度均与风速呈正相关，且同等风速与吹程条件下两者均大于光滑壁面条件，波致气流边界层厚度与风速和吹程均呈正相关.分析了采用风速作为气流动力参数存在不妥的原因，认为采用摩阻风速或切应力作为气流动力参数更具合理性，基于前人研究数据的统计分析，给出了特征粗糙度与风速、吹程和水深的回归关系式.探讨了气流-风浪“同频率”的互馈模式，发现波致气流边界层厚度不只与波长有关，还受波高、波周期和水深等多因素影响，建立了考虑风浪非线性特征的波致气流边界层厚度关系式.;As one of the main driving forces of limited water areas such as lakes and wetlands, the evolution characteristics of airflow are the basis for the study of water-air energy and material transfer, which determines the water environment as well as water ecological pattern of water area, and has important research significance. Using wind tunnel flume, by setting different wind speeds, the response relationship and evolution law of near-surface airflow with wind speed and blowing distance were studied, particularly, flow characteristics under the condition of smooth wall were taken as the test control group, vertical distributions of wind speed, friction wind speed, roughness and so on were analyzed in time domain, and domain frequency change of wind speed and boundary layer thickness of wave-induced airflow are analyzed in the frequency. Results show that the average wind speed near the water surface conforms to the logarithmic distribution, the friction wind speed and characteristic roughness are all positively correlated with the wind speed, and both of them are greater than the smooth wall condition under the same wind speed and blowing distance, and the wave-induced airflow boundary layer thickness is positively correlated with the wind speed and blowing distance. The reasons for the improper use of wind speed as the aerodynamic dynamic parameter are analyzed, and it is considered that it is more reasonable to use friction wind speed or shear stress as the aerodynamic dynamic parameter, and the regression relationship between characteristic roughness and wind speed, blowing distance and water depth is given. The mutual feed model of airflow and wind wave with same frequency is discussed, it is found that the thickness of the wave-induced airflow boundary layer is not only related to the wavelength, but also affected by wave height, wave period and water depth, and the relation formula of the wave-induced airflow boundary thickness considering the nonlinear characteristics of wind and wave is established.

Validation of a multi-physics simulation platform for engine emissions modelling

This paper introduces a comprehensive and systematic Design of Experiments based methodology deployed in conjunction with a multi-physics engine air-path and combustion co-simulation, leading to the development of a global transient simulation capability for engine out NOx emissions. The proposed multi-physics engine simulation framework couples a real-time one-dimensional air flow model with a Probability Density Function based Stochastic Reactor Model that accounts for detailed in-cylinder combustion chemistry to predict combustion emissions. The integration challenge stemming from the different computation complexities and time scales required to ensure adequate fidelity levels across multi-physics simulations was addressed through a comprehensive Design of Experiments methodology to develop a reduction of the slower Stochastic Reactor Model simulation to enable a transient simulation focussed on NOx emissions. The Design of Experiments methodology, based on Optimal Latin Hypercube design experiments, was deployed on the multi-physics engine co-simulation platform and systematically validated against both steady state and transient light-duty Diesel engine test data. The surrogate selection process included the evaluation of a range of metamodels, with Kriging metamodels selected based on both the statistical performance criteria and consideration of physical phenomena trends. The transient validation was carried out on a simulated New European Drive Cycle against the experimental data available, showing good capability to capture transient NOx emission behaviour in terms of trends and values. The significance of the results is that it proves the transient and drive cycle capability of the multi-physics simulation platform, suggesting a promising potential applicability for early powertrain development work focussed on drive cycle emissions.

Natural Convection Modeling in a Solar Tower

Objectives: We present in this study a modeling of thermal laminar convection airflow in a solar tower. Methods: To formulate with precision, the boundary conditions of the solar chimney model chosen, the Cartesian equations are transformed into hyperbolic coordinates. An orthogonal grid is elaborated. It then makes it possible to draw up the diagrams of physique and calculation fields. The computer code uses the heat equation, the vorticity, and the stream function formalism as the boundary conditions for pressure are difficult to set. We use the Boussinesq approximation, which consists in considering that the density (r) of the fluid varies only in the term of the gravity forces, whose variations with temperature, assumed to be linear, generate natural convection. These variations are then translated into an equation of state which relates density to temperature. The system of dimensionless equations is solved by using an intégro-interpolation method referring to finite differences scheme. Findings: The solutions obtained from the dimensionless equations enabled us to determine the space evolution parameters (temperatures and velocities) in the tower according to the Rayleigh number. The fluid temperature and velocity evolution in the collector increase when one moves in the direction of radius decrease. The fluid temperature evolution in the chimney showed that the highest temperature is located at the chimney base while we obtained a parabolic profile of the transverse temperature distribution within the chimney. Finally, the evolution of the fluid velocity in the chimney showed that there was a preferred zone for turbine installation. Novelty : The use of dimensionless geometric parameters is unique and in general, the approach adopted in this paper differs from that encountered in the literature.

Comment on “CFD modelling of air and particle flows in different airway models by Y.H. Kim, Z.B. Tong, H.K. Chan, R.Y. Yang, Journal of Aerosol Science, 134 (2019) 14–28”

Comment on “CFD modelling of air and particle flows in different airway models by Y.H. Kim, Z.B. Tong, H.K. Chan, R.Y. Yang, Journal of Aerosol Science, 134 (2019) 14–28”

THE COMBUSTION ENGINE INTAKE MANIFOLD CFD MODELING DEPENDING ON THE AIRBOX CONFIGURATION

The aim of the article is to present the possibilities of application of computational fluid dynamics (CFD) to modelling of air flow in combustion engine intake manifold depending on airbox configuration. The non-stationary flow occurs in internal combustion engines. This is a specific type of flow characterized by the fact that the variables depend not only on the position but also on the time. The intake manifold dimension and geometry strongly effects intake air amount. The basic target goal is to investigate how the intake trumpet position in the airbox impacts the filling of the combustion chamber. Furthermore, the effect of different distances between the trumpet neck and the airbox wall in this paper will be compared.

Airflow modelling predicts seabird breeding habitat across islands.

Wind is fundamentally related to shelter and flight performance: two factors that are critical for birds at their nest sites. Despite this, airflows have never been fully integrated into models of breeding habitat selection, even for well-studied seabirds. Here, we use computational fluid dynamics to provide the first assessment of whether flow characteristics (including wind speed and turbulence) predict the distribution of seabird colonies, taking common guillemots Uria aalge breeding on Skomer Island as our study system. This demonstrates that occupancy is driven by the need to shelter from both wind and rain/wave action, rather than airflow characteristics alone. Models of airflows and cliff orientation both performed well in predicting high-quality habitat in our study site, identifying 80% of colonies and 93% of avoided sites, as well as 73% of the largest colonies on a neighbouring island. This suggests generality in the mechanisms driving breeding distributions and provides an approach for identifying habitat for seabird reintroductions considering current and projected wind speeds and directions.

Modeling of Air Flow Over a Generic Aircraft Carrier With and Without Island Structure

The study of external aerodynamics of an aircraft carrier is of utmost importance in ensuring the safety of aircraft and pilots during take-off and recovery. The velocity deficit in the forward direction and the downwash together combine to give a sinking effect to the aircraft, along its glideslope path and is known as the ‘burble’ in naval aviation parlance. This phenomenon is primarily responsible for the potential increase in pilot workload on approach to the aircraft carrier. There is little literature in the open domain regarding ways and means to alleviate the burble effect. Unlike in the case of the automobile industry, which has the generic ‘Ahmed body’ and for the frigates/destroyers, for which there is the Simplified Frigate Ship (SFS), on which experiments and validation through CFD could be carried out, by researchers from all over the world, there is no generic Aircraft Carrier model for carrying out experiments and validation of CFD codes. The aim of this study is to define the Generic Aircraft Carrier Model (GAC), as developed at IIT Delhi, and to carry out numerical studies on the GAC and a variant of GAC without the island, BGAC (Baseline GAC), to assess the contribution of the island to the burble behind an Aircraft Carrier. This study gives a quantitative estimation of the effect and contribution of individual components of an Aircraft Carrier (like flight deck, island, etc.) to the burble behind the carrier, and would give a Naval Ship Designer an understanding of the effect of the geometrical configuration of the flight deck and the island on generation of the burble behind the carrier, which could aid the designer in potentially reducing the pilot workload.

Eulerian-Lagrangian simulation of wood flour and wind distribution during the impulse-cyclone airflow drying process

To improve the particle transport computational fluid dynamics models of impulse-cyclone airflow drying systems, a Eulerian-Lagrangian discrete particle model (commercial code ANSYS Fluent 2019 R1) was extended to describe the temperature field, airflow velocity field, and particle distribution in the impulse and cyclone dryers. The results showed that the velocity of the airflow considerably changed after wood flour was added into the system, with an approximate velocity difference between the particles and airflow of 2 m/s. An increased feed rate led to a backflow area at the bottom of the cyclone dryer, which caused reflux and a long residence time of the wood flour in and near the cyclone dryer. By comparing the calculated temperature, velocity, and time curves with the measured temperature and velocity sensor values, the error between the simulated value and the experimental value was only approximately 15%. The current work verifies that the Eulerian-Lagrangian discrete particle model of the impulse-cyclone airflow drying process established via the computational fluid dynamics simulation method was effective. The conclusion provides a reliable theoretical basis for the technological design of impulse-cyclone airflow drying systems, thus providing a way to optimize the structure of impulse-cyclone airflow drying systems in the future.

Numerical modeling of cough airflow: Establishment of spatial–temporal experimental dataset and CFD simulation method

In this study, the boundary conditions to simulate the cough airflow of a human using computational fluid dynamics (CFD) simulation have been defined. Spatial–temporal datasets of cough airflow were obtained from particle image velocimetry (PIV) experiments conducted previously, and an ensemble-average analysis was performed for CFD calculations and to validate simulated results. The air velocity corresponding to the boundary conditions for the opening of the mouth for CFD simulation could not be obtained directly from PIV experiments. Hence, the experimental results of airflow near the mouth were used to explore the boundary conditions of the cough for CFD simulation, assuming that the velocities near the mouth and the boundary conditions are highly correlated. The time-series velocity boundary conditions for the simulation of cough were explored using two methods. The conditions for Method 1 were closer to that for the overall cough airflow distribution obtained from the experimental datasets, while the conditions for Method 2 most closely matched the maximum velocity at a specific location of the cough airflow. The cough airflow reproduced by CFD using Method 1 showed RMSE values of 0.24–0.32 m/s compared to the experimental results when the maximum velocities at boundary conditions were 15.5–15.8 m/s. Moreover, for Method 2, the maximum velocity was reproduced with an error of 0.02 m/s. This study obtains the detailed boundary conditions for cough simulation, which, coupled with droplets and droplet nuclei dispersion models, can be applied to investigate the risk of infection and transmission routes of human cough.

Moisture safety in ventilated cathedral roofs

Cathedral roofs are commonly used when constructing small houses in Sweden. In contrast to roof constructions with a cold attic, where frequent moisture damage has been noted, the cathedral roof is difficult to access for inspection. Furthermore, Swedish building regulations sets high demands regarding moisture safety, although there are no clear guidelines for their compliance. Hence, designing a cathedral roof must be done with great care. Previous studies investigating moisture safety in cathedral roofs, applies a constant air exchange in the ventilated air cavity. In this study a cathedral roof, ventilated from eave to eave, was analysed by examining the relevance of considering the variation in cavity air flow when conducting coupled heat and moisture calculations. The varied cavity air flow was calculated in an air flow model, considering wind and thermal buoyancy as driving forces. The accuracy of moisture safety assessments using the MRD model via hygrothermal calculations in WUFI Pro were also studied. Comparing moisture calculations with measurements showed high similarity when using a model with constant cavity air flow, and even higher resemblance when using a model with varied air flow. When actual conditions are sought, the study indicated that pinpointing important parameters, such as initial moisture content and moisture related material properties, would further increase precision in moisture calculations.