Airflow Model Research Articles

Equation discovery of dynamized coefficients in the k-ε model for urban airflow and airborne contaminant dispersion

Urban airflow and pollution modeling using steady Reynolds-averaged Navier-Stokes (SRANS) with two-equation models has faced accuracy challenges, limiting its reliability for sustainable city design. The low accuracy has been attributed to SRANS ill-conditioning, the linear eddy viscosity hypothesis, and uncertainty contributed by empirical formulations and coefficients. Many studies have attempted to modify the two-equation models specifically for urban problems by correcting the model formulations and calibrating the coefficients. However, these corrections often improve accuracy for targeted regions or quantities while diminishing it elsewhere. This stems from inflexibility in the model form. To mitigate the trade-offs and improve generalizability, this study introduces multiple dynamic correctors to the k-ε coefficients for expanded design space. In particular, the robustness and redistributability of the corrected model were considered by retaining the theoretical interpretation of turbulence and employing symbolic correctors. The gene expression programming technique was employed for equation discovery. The increased model flexibility mitigated the trade-offs in accuracies for different quantities in the training case. The generalizability of a corrected model was evaluated for airflow and dispersion around a single building, a building array, and a group of complex buildings. The corrected model performed consistently for the three flow types and exhibited generalizability.

Performance of the WRF Model at the Convection‐Permitting Scale in Simulating Snowfall and Lake‐Effect Snow Over the Tibetan Plateau

AbstractThis study investigated the performance of the Weather Research Forecasting (WRF) model at 4‐km horizontal grid spacing in simulating precipitation, 2 m air temperature (T2), snowfall, and lake‐effect snow (October 4–8, 2018) over the Tibetan Plateau (TP). Multiple simulations with different physical parameterization schemes (PPSs), including two planetary boundary layer schemes (Yonsei University and Mellor–Yamada–Janjic), no cumulus and multi‐scale Kain‐Fritsch, two land surface models (Noah and Noah‐MP), and two microphysics schemes (Thompson and Milbrandt), were conducted and compared. Compared with gauge observations, all PPSs simulate mean daily precipitation with mean relative errors (MREs) of 27.7%–53.6%. Besides, spatial correlation coefficients (SCCs) between simulated and observed mean daily precipitation range from 0.56 to 0.71. For simulations of T2, all PPSs perform similarly well, even though the mean cold biases are up to about 3°C. Meanwhile, all PPSs exhibit acceptable performance in simulating spatial distributions of snow depth, snow cover, and snowfall amount, with SCCs of 0.37–0.65 between simulations and observations. However, the WRF simulations significantly overestimate snow depth (∼0.4 cm mean error) and snowfall amount (MREs >372%). The Milbrandt scheme slightly outperforms the other PPSs in simulating snow‐related variable magnitudes. Due to their inaccurate temperature and airflow modeling over the lake surface and its surroundings, none of the WRF simulations well reproduce the characteristics that more snow occurs over the lake and downwind area. Overall, this study provides a useful reference for future convection‐permitting climate modeling of snow or other extreme events when using the WRF model in the TP and other alpine regions.

Computational modelling of airflow in distal airways using hybrid lung model

ABSTRACT A major challenge in computational fluid dynamics (CFD) modelling of the human respiratory system is allowing for the variation of geometric scale. A methodology is proposed that enables CFD analysis from the middle through the distal airways to the alveolar level. The methodology relies on a hybrid lung geometry integrating a primary tracheobronchial tree (TBT) up to the fifth generation (section 1) and distal airway (section 2). Section 1 comprises of the middle airways reconstructed from patient CT scans. Section 2 comprises of the distal airway branching tree generated based on deterministic algorithm. The hybrid model allows the application of physiologically relevant boundary conditions in lieu of simplistic approximations used in previous studies. Two different breathing conditions are considered adapted from previous studies, representing resting and exercise activity. The predicted flow variables are assessed for numerical accuracy and validated by comparison with published experimental and numerical data.

An Evaluation of Inflow Profiles for CFD Modeling of Neutral ABL and Turbulent Airflow over a Hill Model

The implementation of the wind turbine is a major issue in the wind engineering sector. However, the presence of wind turbines in the lower part of the atmospheric boundary layer (ABL) requires an appropriate study for the simulation of turbulent airflow in the wind farm situated on hilly terrain. The use of precise Computational Fluid Dynamics (CFD) simulations for the ABL flow is vital for numerous applications, such as wind energy, building, urban planning, etc. To achieve accurate results, it is imperative that the inlet boundary conditions produce vertical profiles that keep a uniform horizontal distribution (with no streamwise gradients) in the upstream region of the computational domain for all important parameters. A development approach is proposed herein, focused on the imposition of two different inlet profiles when used in combination with the rough z0-type scalable wall function. The horizontal homogeneity of these profiles has been verified by 2D Reynolds averaged Navier-Stokes (RANS) through the examination of a neutral ABL in an empty computational domain using the k-ε turbulence model. The findings indicate that the use of this modeling approach can yield relatively consistent homogeneity of neutral ABL for both inlet boundary conditions. Subsequently, sensitivity analyses were performed on the inflow profiles to forecast the evolution of the bottom half of an idealized truly-neutral ABL and to accurately capture the complex dynamics of atmospheric flows over hilly terrain. This study compares the results with the CRIACIV (Inter-University Research Centre on Building Aerodynamics and Wind Engineering) boundary layer wind tunnel experimental data, showing that the inflow profiles and the presence of topographic complex have a significant impact on air velocity, turbulent kinetic energy and turbulence intensity in the x-direction. The results obtained are in good correlation with published experimental data in the presence of the hill surface.

CFD model for airflow in a subway station compared to on-site measurements: The challenges of as-built environment

Understanding the contribution of piston effect and train-induced airflow to the ventilation of underground subway stations is essential to design efficient ventilation systems. To this aim, numerical models using computational fluid dynamics (CFD) have been used to recreate existing stations with a number of simplifying assumptions. However, the large variety of station configurations as well as types of sources influencing the airflow makes the generalization to other cases difficult. This study intends to predict numerically the train-induced wind affecting the climate of subway stations perceived on the platforms, and a comparison of these numerical predictions with field tests in an actual station is provided and extensively discussed.A simplified geometry of a station, where the ventilation is mainly realized by the piston effect caused by the train movement, is used to implement a scenario of a train passing through the station, with dynamic meshing techniques, and background wind is included in one configuration. Experimental measurements at 9 locations along the station's platform, repeated in order to improve statistical accuracy and the reproducibility of the results, provide data that can be compared with the corresponding numerical simulation. Numerical to experimental comparison is based on quantification of the peaks due to ingoing and outgoing trains through parameters like peak value, skewness and kurtosis. It is found that the main features of the airflow are well captured by the model, but the differences observed also highlight the challenges of simulating the as-build environment. Several non-dimensional metrics proposed in this paper can be used for comparison with other papers, so that a validated numerical model can be a relevant tool to calculate different velocity scenarios for trains and within different station architectures, supporting the design of ventilation systems to improve the comfort and safety of passengers.

CFD modeling of dynamic airflow and particle transmission in an aircraft lavatory

CFD modeling of dynamic airflow and particle transmission in an aircraft lavatory

Mathematical Model of Airflow and Solid Particles Transport in the Human Nasal Cavity

Mathematical Model of Airflow and Solid Particles Transport in the Human Nasal Cavity

Improved Air Valve Selection through Better Device Characterization and Modeling

Employing a set of well-chosen and maintained air valves is a widely recommended strategy for air management in pressurized pipelines. However, precisely characterizing, modeling, and sizing air valves for the various functions they serve can be a demanding task. This paper considers the key challenges of air valve characterization in light of several potential complications. The paper summarizes and gives context to location criteria for air valves and discusses some of the common pitfalls in selecting such devices. Moreover, the effectiveness of four air flow models in representing data from characterization tests is evaluated. Not surprisingly, the most complex model with an adjustable polytropic exponent is found to have the best curve fitting capability, although the simpler isentropic model fits experimental data reasonably well. However, employing a fixed polytropic exponent of 1.20 tends to underestimate air flows for relatively intense differential pressures, while the incompressible model poorly represents air inflow. The paper also shows how representative air flow curves may be constructed even if only scant characterization data are available.

Mathematical model of air flow movement in a motorized filter respirator

Purpose. Development of a mathematical model of the air flow movement in a motorized filter respirator (hereinafter referred to as MFR), which allows ensuring the control of the fan parameters, taking into account external and internal influences on the duration of the protective action and favourable operating conditions. Methodology. To describe linear objects of the “input-output” type, it is convenient to use their transfer functions as mathematical models. In this case, to determine the mathematical description of the MFR operation, two tasks need to be solved. The first is related to finding the structure of the mathematical model, and the second involves determining the coefficients of the polynomials in the numerator and denominator of the transfer function that describes the motion of the air flow in the MFR. Findings. A mathematical model of airflow in a MFR has been developed in the form of a transfer function of the third order; it can be used to develop a pressure control system for the air in the under-mask space in accordance with the user’s work mode in order ensure comfortable working conditions. The presented mathematical model of airflow in the MFR differs from the existing approaches by taking into account the influence of the following external and internal parameters of the system on the performance indicators: the user’s work mode, atmospheric pressure, filter resistance, pressure drop in air ducts with the effect of air accumulation in the under-mask space based on the “capacity-resistance” principle. Numerical coefficients of the mathematical model of airflow in the air duct of the MFR have been determined, which allow adjusting the number of fan rotations according to the time of operation, the increase in resistance on the filters, and the operating mode. Originality. A correlation has been established between the external and internal parameters of the MFR: atmospheric pressure, pressure drop in the air duct, filter resistance, and the user’s work mode with the effect of air accumulation in the sub-mask space reflected according to the “capacity-resistance” principle. Practical value. The parameters of the mathematical model have been determined, which can be used when developing a control system for the airflow movement in the MFR: changes in air flow rate in accordance with different conditions of physical exertion of the user when performing professional activities.

Effect of Variations in Velocity Air Intake Cyclone Dimensions on Motorcycle Torque and Power

The Velocity Air Intake System is an important component in a motor vehicle engine, particularly in a 155cc engine. Its function is to optimize the airflow process to the throttle body or carburetor. However, many users or people tend to overlook the significance of improving engine performance by varying the model or replacing the velocity air intake system itself. One common issue is the diameter and shape of the airflow model, which can affect the power, torque, and exhaust emissions produced. Installing a velocity air intake system is one approach to achieve an efficient air delivery process into the combustion chamber. In our research conducted using a dyno test on a 155cc four-stroke engine, the results showed that using a 46 mm size yielded the highest power of 11.03 Hp and produced a torque of 12.39 N.m. Using a 47 mm size resulted in 11.02 Hp and decreased the torque to 12.28 N.m. With a 48 mm size, there was a decrease in power to 11.00 Hp and an increase in torque to 12.72 N.m, while using a 45 mm size led to a decrease in power to 10.09 Hp and produced a torque of 11.31 N.m.

Modelling the influence of beach building pole heights on aeolian morphology and downwind sediment transport

Buildings on beaches either sit directly on the sediment surface or are placed on poles. These structures alter near-bed airflow around them. To quantify the influence of pole height on airflow, resulting bed morphology around these buildings and sediment fluxes passing these buildings towards the dunes, three-dimensional simulations were performed. To compute airflow, we used the open-source computational fluid dynamics software OpenFOAM. For sand transport and bed level changes, we used the Exner equation combined with Bagnold's sediment transport flux formulation, and a newly-developed model that couples the airflow model with the sediment transport model AeoLiS. In the simulations, we modelled a row of ten full-scale beach buildings on a flat/smooth sandy bed, with a constant gap size between neighbouring buildings, varying the pole heights between simulations. Our findings showed that elevated buildings affect the wind speed in a larger region, both upwind and downwind, compared to buildings without poles. The model simulations showed that airflow accelerated both underneath the elevated buildings and through the gaps between the buildings. Moreover, besides flow acceleration underneath the buildings, the elevated buildings induced slightly higher flow acceleration through the gaps between buildings. Depending on pole height to building width ratio, elevated buildings could both decrease and increase the downwind sediment flux compared to an undisturbed situation. For ratios between 0 and 0.5, downwind fluxes were reduced in a zone between 5 and 40 m behind the buildings, while for ratios above 1.3, downwind fluxes were observed to increase in a zone up to 20 m behind the buildings. Also, this study emphasizes the importance of selecting an optimal pole height to maximize the benefits of beach buildings in terms of passing on sediment transport towards the dunes.

Large-eddy simulation of buoyant airflow in an airborne pathogen transmission scenario

Indoor airflow patterns and the spreading of respiratory air were studied using the large-eddy simulation (LES) computational fluid dynamics (CFD) approach. A large model room with mixing ventilation was investigated. The model setup was motivated by super-spreading of the SARS-CoV-2 virus with a particular focus on a known choir practice setup where one singer infected all the other choir members. The room was heated with radiators at two opposite walls in the cold winter time. The singers produced further heat generating buoyancy in the room. The Reynolds number of the inflow air jets was set to Re=2750, corresponding to an air-changes-per-hour (ACH) value of approximately 3.5. The CFD solver was first validated after which a thorough grid convergence study was performed for the full numerical model room with heat sources. The simulations were then executed over a time of t=20 min to account for slightly more than one air change timescale for three model cases: (1) full setup with heat sources (radiators+singers) in the winter scenario, (2) setup without radiators in a summer scenario, and (3) theoretical setup without buoyancy (uniform temperature). The main findings of the paper are as follows. First, the buoyant flow structures were noted to be significant. This was observed by comparing cases 1/2 with case 3. Second, the dispersion of the respiratory aerosol concentration, modeled as a passive scalar, was noted to be significantly affected by the buoyant flow structures in cases 1–2. In particular, the aerosol cloud was noted to either span the whole room (cases 1–2) or accumulate in the vicinity of the infected singer (case 3). Turbulence was clearly promoted by the interaction of the upward/downward moving warmer/cooler air currents which significantly affected the dispersion of the respiratory aerosols in the room. The study highlights the benefits of high-resolution, unsteady airflow modeling (e.g. LES) for interior design which may consequently also impact predictions on exposure to potentially infectious respiratory aerosols.

Heat and species map prediction for the generic MEA using an air node model derived from high level requirements

Current developments to implement the More Electric Aircraft (MEA) result in a fundamental change of the aircraft systems architecture. Components may be resized or new components may be introduced. This results in new challenges for the thermal management and safety assessment of systems and therefore parametric and fast simulations tools will become crucial to explore the entire design space. The effects of component heat dissipation on airflow in the aircraft fuselage can be qualified using a zonal simulation model. Zonal airflow models subdivide the indoor space into typically 102 zones exchanging air. This allows to predict the impact of systems locations, ventilation and cooling strategies on the thermal management and safety considerations in an early design stage. This paper presents the setup of such an aircraft zonal model based on high-level requirements for a MEA of regional airplane size. These requirements cover the number of passengers, the flight profile and system components to be integrated, like e.g. the battery. Additional requirements are derived from standards for example providing information on required airflow rates and temperatures in the cabin. These requirements are translated into a geometry, ventilation pattern and systems layout. The model application is demonstrated on the example of the safety consideration in case of a battery failure leading to exhaust of harmful gas. This is done by comparing the gas dispersion for two different battery positions in the aircraft.

Model and simulator of inlet air flow in grinding installation with electromagnetic mill

Comminution of raw materials consumes great shares of energy and operating costs of production and processing plants. Savings may be achieved, e.g., by developing new grinding equipment, such as the electromagnetic mill with its dedicated grinding installation; and by applying efficient control algorithms to these elements. Good quality control relies on mathematical models, and testing of versatile control algorithms is much simplified if a plant simulation environment is available. Thus, in this research, measurements were collected at the grinding installation with electromagnetic mill. Then, a model was developed that characterised the flow of transport air in the inlet part of the installation. The model was also implemented in software to provide the pneumatic system simulator. Verification and validation tests were conducted. They confirmed the correct behaviour of the simulator and good compliance with the experimental data, for both steady-states and transients. The model is then suitable for design and parametrization of air flow control algorithms and for their testing in simulation.

Verification of the Mathematical Model for Calculating the Air Flow Velocity Fields for Displacing Ventilation of Rooms of Complex Configuration

Statement of the problem. The purpose of the article is to verify the developed mathematical model of conformal mapping of air flows, which constructs air velocity fields during displacement ventilation of rooms of complex configuration with partitions. Results. An experimental setup has been developed to study the physical model of a room with partitions, which allows performing physical modeling of air flows. The comparison of analytical and experimental results of calculating the air velocity in randomly selected points of the studied area is carried out. Conclusions. The verification results show that the developed model, with a sufficiently high accuracy, allows one to determine the air flow velocity with a vortex-free flow and its insignificant disturbance. An increase in the speed and deviation of the flow trajectory from the level lines leads to an increase in the calculation error.

Application of Particle Image Velocimetry and Computational Fluid Dynamics Methods for Analysis of Natural Convection over a Horizontal Heating Source

The objective of this article is to address the challenges associated with visualizing air flow over a heating source in an open laboratory environment. The study uses a combination of experimental visualization and numerical simulation techniques to generate a 3D model of the air flow and heat transfer between the heating source and the environment via natural convection. The Particle Image Velocimetry method is used to experimentally visualize the air flow, which is known for its benefits of high speed and accuracy, and for its ability to avoid disturbing the flow of the fluid being investigated. The data obtained from this experimental method are used as input for numerical simulations using the Ansys Fluent program. The numerical simulations identify air vortices and other elements that disrupt the airflow in the laboratory environment. The resulting 3D model accurately represents the actual situation in the laboratory and could be further optimized by adjusting parameters such as the output of the heater and the heating source temperature. These parameters play a crucial role in ensuring thermal comfort in the laboratory environment, which is of utmost importance for user comfort. In conclusion, the study provides valuable insights into the visualization of air flow over a heating source and demonstrates the effectiveness of combining experimental and numerical simulation techniques to generate accurate 3D models of air flow and heat transfer.

Towards the evaluation of heat and mass transfer in pipe flows with cocurrent falling films using One‐Dimensional Turbulence

AbstractTurbulent mixed convection in an air‐water system is evaluated with a novel numerical solver implementing the stochastic One‐Dimensional Turbulence (ODT) model in a turbulent air flow surrounded by a laminar cocurrent water falling film in a cylindrical geometry. The ODT model is used as a reduced order surrogate model for the effects of turbulent advection, turbulent heat flux, and turbulent mass‐flux within a one‐dimensional domain. An ad‐hoc temporal‐to‐spatial transformation relying on the bulk flow gas velocity is used to obtain streamwise‐dependent statistics of the flow. The ODT simulation results are compared to simulations obtained with the assumption of a quasi‐laminar one‐dimensional gas flow, and to Reynolds‐Averaged Navier‐Stokes (RANS) reference data for a cocurrent water falling film evaporator [1]. The results show that the turbulent transport plays a decisive role in the estimation of interface gradients of temperature and vapor mass fraction. Although ODT predicts global quantities such as the interface temperature in a reasonable way, the model falls short of successfully predicting streamwise‐dependent radial profiles. Despite the shortcomings, the framework presented here is the first stepping stone towards the evaluation of complex multiphase momentum, mass, and heat transfer couplings with full scale resolution on potential evaporative devices. The model, thus, provides valuable information with minimal empiricism on the dynamics of the small scales for pioneering engineering applications.

Numerical investigation on the performance of a Solar Chimney Power Plant System (SCPP)

AbstractIn this work, a parametric two‐dimensional computational fluid dynamics (CFD) analysis of solar chimney power plant was performed to describe the physical mechanism in order to establish realistic predictions for the operation of such plants in different location in Algeria. The developed numerical model includes a solar radiation model within the collector; an energy storage model; an air flow and heat transfer model, and a turbine model. It is based on the solution of the Navier‐Stokes equation for turbulent flow using the standard k − ϵ model. The Boussinesq model was adopted in this simulation for the density of the fluid. The boundary conditions were adapted according to the selected sites and the effect of this on the SCPP performance was studied. The numerical simulation was performed using the commercial computational fluid dynamics (CFD) code “Ansys Fluent 19.2”.

Contribution to the modelling of air flows in a conical inlet drying chamber

The main objective of this study is to provide input on the mesh and temperature distribution inside the drying chamber for a building-integrated dryer for food preservation to obtain a uniform temperature profile. For this, we varied the angle of inclination of 20° and 30° subsequently we also varied the speed of the air flow of (1m/s; 1,2 m/s; 1,5 m/s; 1,7 m/s and 2 m/s), the temperature at the level of the walls is the ambient temperature it is 25°C and the air inlet temperature is set at 55°C. The results obtained showed that the temperature distribution inside the different drying chambers is almost uniform for an inclination of 30° against for an inclination of 20° it is uniform on the bend of the cone of the diffuser but not in the drying chamber. This uniform distribution reduces the drying time of the product. It can therefore be concluded that the variation in tilt angle and drying speed has a significant effect on the drying time of the product.

Thermal management of a prismatic lithium battery pack with organic phase change material

BackgroundThis article examines a T-shaped lithium-ion battery pack (BPC) consisting of six prismatic cells using the finite element method (FEM). An optimal model is introduced for batteries’ thermal management (THMT) by changing the position of the inlets and outlets. MethodsThe outlet is where the fully developed airflow leaves, and the walls use the no-slip boundary condition. The batteries are placed in an enclosure filled with phase change material (PCM) to create temperature uniformity on the batteries. The hydrodynamic and thermal modeling of airflow and the melting and freezing of PCM are performed in this study using the COMSOL program. Significant findingsThe results demonstrate that the batteries’ maximum temperature (TMX) changes by changing the location of the inlets. Changing the position of inlets also affects the melting and freezing of the PCM, and better temperature uniformity on the batteries may be achieved using some models. The M4 model, in which the inlet and outlet are on the left and right sides, and an outlet is in the center, is the most appropriate model for industrial applications.