Numerical Modelling Of Airflow Research Articles

Computational study on effects of jet fans to traffic force in highway tunnel

Traffic force induced by the piston effect of moving vehicles is a major driving force to the airflow in road tunnels. To ensure an adequate flow rate in the tunnel, an accurate estimation to the traffic force is necessary. This work investigates the influence of jet fans to the traffic force of a large vehicle in a long highway tunnel. A numerical model of airflow in the tunnel is established based on RANS (Reynolds Averaged Narvier-Stokes) equations, and dynamic mesh method is utilized to simulate the moving vehicle. Results show that, traffic force is significantly amplified when the vehicle passes the jet fans, which can be explained by the non-uniform velocity profile under the entrainment of high-speed jets. A parametric analysis is conducted to the effects of initial jet velocity, vehicle speed and ventilating velocity of tunnel. Finally, an improved correlation is proposed to evaluate the drag coefficient and traffic force of the vehicle within the affecting range of air jets.

Numerical modeling of air flow inside the human nose cavity

The complex structure of the human nasal cavity makes it difficult to study the flow of air in it, therefore, at present, mathematical and computer modeling is used for this purpose. These studies are relevant due to the development of inhalation methods for introducing drugs into the nose, with the help of which operations can be performed. Within the framework of the Navier-Stokes system of equations, temperature and concentration using the ANSYS Fluent application, a three-dimensional test calculation of the air flow in the human nasal cavity was carried out at various modes of inhalation, normal and during exercise. A laminar model was used to close the Navier-Stokes equations, and the SIMPLE method was used to perform the relationship between velocity and pressure. In the graphics package AutoCAD, a geometric three-dimensional model of the nasal cavity was built, reconstructed from images of the nose in coronary sections. As a result of numerical simulation, the fields of velocity, pressure, temperature and concentration were obtained. The results obtained were compared with the experimental data from [10] and the numerical results from [3]. The analysis of these results in terms of the influence of the structure of the nasal cavity on the structure of the flow. The results obtained agree with the experimental data. It was found that the inhaled air is heated and humidified to the state of the nasal tissue, the shells increase the rate of local transfer of heat and moisture by improving mixing and maintaining thin boundary layers, the capacity of a healthy nose exceeds the requirements necessary for conditioning the inhaled air under normal breathing conditions.

Some Tips on Numerical Modeling of Airflow and Fires in Road Tunnels

The efficiency of tunnels systems is often evaluated using numerical simulations. This concerns both to normal and emergency mode of tunnel systems operation. Therefore the safety level of tunnel users may depend on the quality of numerical models being built. The most often studied areas cover the researches on natural and forced airflows in the normal mode and on fire development and smoke spreading in the emergency mode as well as modeling of fan operation. Thus, many software packages implementing Computational Fluid Dynamics (CFD) are applied here. Despite the available software is recognized as reliable, the problem arises because the built numerical models should be validated at least partially with experimental data. There is a shortage of experimental data from real tunnels due to high costs and many organizational or formal difficulties. Some researchers use data from scaled experiments, but this leads to problems connected with scaling. The paper presents the application of two widely used software packages—Fire Dynamics Simulator (FDS) and ANSYS Fluent to reproduce some scenarios of the operation of a tunnel ventilation system for normal and emergency mode. Most of results were compared with data obtained by own full scale measurements or data available in literature. Some practical issues concerning the application of FDS and ANSYS Fluent were discussed as well.

Numerical Modeling of Air Flow in a Cabinet Dryer Equipped by Deflector Plates

Abstract In this study, air deflector plates were used in order to increase the air elapsed time in the chamber. The air flow pattern was simulated using computational fluid dynamics. The geometry of the chamber was produced in 2D and meshed by triangular and quadrilateral elements, boundary conditions were defined and the governing equations solved. Modeling of flow without any deflectors depicted the air flowed to the chamber conducted to the outlet without any distortion. Air vortices were generated when the deflectors defined in model. To evaluate the influence of deflectors on drying period, constructed plates installed in the dryer chamber and melon slices were dried when deflectors used or not. Simulation results showed magnitude of the air velocity was increased and temperature uniform distribution developed on the surface of trays. The outlet temperature was also decreased up to 10 % and drying time reduced to 22 % when the deflectors were employed.

Numerical modeling of airflow over column of vehicles using Ansys® package

Growing needs in transportation determinate systems development which improve efficiency of travel and reduce harmful influence to environment. Computational Fluid Dynamic (CFD) uses numerical analysis to find optimal solutions in terms of chosen objective function. Time save and reduce costs for experiments on prototypes are one of the advantages of this method. The aim of this research is to analyze airflow around different motor vehicles which are moving together in the same direction. To reduce fuel consumption and, at the same time, decrease negative influence to environment, the primary target was reducing total drag force during a ride. The vehicles were set in a column - one after another. In this work considered three types of vehicles: Car, Van and a Truck. Presented vehicles were organized into appropriate groups, creating different configuration. Additional parameter in simulation was distance between vehicles. Simulations of singular vehicles were also done. It allows to evaluate influence of moving vehicles in a column for generated drag force. Described traffic situation were modeled and numerically calculated using ANSYS® package. The purpose of this work was to assess the impact of the distance between vehicles, in a given configuration, for generated drag force.

Improving the Curing Cycle Time through the Numerical Modeling of air Flow in Industrial Continuous Convection Ovens

Drying, curing, baking are few of the manufacturing processes that require the use of impingement ovens. For the manufacturing of large batches typically continuous flow ovens are used that are part of an automated conveyor processing line. The retention time for a product to be treated in the oven usually drives the production efficiencies (i.e. energy usage or lead times). In many processing lines though, the ovens are not designed and run in the most efficient way, and as a result become the “bottleneck” process phase. In such ovens, usually the hot air is ejected from rows of nozzles perpendicularly to the moving product. In the most advanced designs the ovens are divided in zones, with each zone having different targeted operating temperature. The optimization of the manufacturing process is difficult to be experimentally determined due to several reasons: the length of the ovens and the complexity of the movement of the product in and out of the oven are the most challenging ones. The main objective of this paper thus is the development of a Computer Fluid Dynamics model for simulating the thermal - transfer efficiency of an existing hot-air convection oven used to produce continuous products. The model is used for the estimation of the maximum speed that the conveyor belt can be run, and further investigate possible improvements on the design of the oven for the reduction of the cycle time. The results can be useful during the overview of the actual production and manufacturing rules.

Numerical modelling of airflow and gas dispersion in the pit headspace via slatted floor: Comparison of two modelling approaches

The slatted floor system is popular in pig and cattle housing. Ammonia and odour are mostly emitted from the slurry pit under the slatted floor. In order to develop solutions to reduce this part of emissions, a better understanding of air distribution and pollutant transportation mechanisms is required. Computational fluid dynamics (CFD) is a useful technique to investigate the air motion, and transport of pollutants between room and pit headspaces via the slatted floor. However, there is a practical issue related to modelling the thousands of small slot openings in the real livestock building for CFD simulation. It is unrealistic to simulate the slatted floor with geometry details due to the large grid number and the limited computer capacity. In this study, a simplification model using porous media to represent a scaled slatted floor was developed. To assess the feasibility of this simplification, the proposed porous media model (SP) was compared with the direct geometry model (SD) and experimental data. The results showed that the porous media model was able to estimate the air velocities but not the turbulent kinetic energy. Both models predicted rotating flows under the slatted floor. A clear vertical air motion above the slatted floor was found for SP results but no such trend for SD results. The mechanism of the pollutant transportation, including the process of pollutant escaping from the pit and retention time of pollutant inside the pit headspace, was found to be inconsistent for SD and SP models. For SD, the dominant removal mechanism of transporting pollutants from the headspace to the free stream was mean flow transportation whereas it was turbulent flow transportation in SP. Higher emission rate and shorter retention time of pollutant in the headspace was obtained by using SP compared to SD. In general, though the porous media approach cannot reveal the pollutant transport mechanism, it can predict the velocity magnitude. In addition, it was found that the orientation of slats to stream flow direction plays an important role on airflow pattern and pollutant distribution inside the pit headspace.

Numerical modeling airflow in soil with impact of groundwater

In order to simulate the airflow in anhydrous case and the water-air flow in groundwater case, a numerical model of airflow in soil was developed. For the nonlinearity of the governing partial differential equation, the corresponding discretization and linearization methods were given. Due to the mass transfer between air-phase and water-phase, phase states of the model elements were constantly changing. Thus, parameters of the model were divided into primary ones and secondary ones, and the primary variables changing with phase states and the secondary variables can be obtained by their functional relationship with the primary variables. Additionally, the special definite condition of this numerical model was illustrated. Two examples were given to simulate the airflow in soil whether there was groundwater or not, and the effectiveness of the numerical model is verified by comparing the results of simulation with that of experiment.

Numerical Modelling of Airflow and Temperature Distribution in a Living Room with Different Heat Exchange Conditions

Numerical Modelling of Airflow and Temperature Distribution in a Living Room with Different Heat Exchange ConditionsNumerical mathematical modelling of the indoor thermal conditions and of the energy losses for separate rooms is an important part of the analysis of the heat-exchange balance and energy efficiency in buildings. The measurements of heat transfer coefficients for bounding structures, the air-tightness tests and thermographic diagnostics done for a building allow the influence of those factors to be predicted more correctly in developed numerical models. The temperature distribution and airflows in a typical room (along with the heat losses) were calculated for different heater locations and solar radiation (modelled as a heat source) through the window, as well as various pressure differences between the openings in opposite walls. The airflow velocities and indoor temperature, including its gradient, were also analysed as parameters of thermal comfort conditions. The results obtained show that all of the listed factors have an important influence on the formation of thermal comfort conditions and on the heat balance in a room.

Air velocity characteristics within vented pallets loaded in a refrigerated vehicle with and without air ducts

During transport using refrigerated vehicles, this being a vital link in the cold chain, the maintaining of even temperature throughout the cargo is essential in order to preserve the quality, safety and shelf life of perishable food. Within the refrigerated container, the temperature level and its homogeneity are directly governed by airflow patterns. The design of the air-distribution system should allow these airflows to compensate heat fluxes exchanged through the insulated walls or generated by the products. In this paper, a reduced-scale model and CFD predictions were used to investigate experimentally and numerically the airflow patterns within a typical refrigerated truck configuration loaded with vented pallets filled with spherical objects. The experiments were carried out using a laser Doppler velocimetry and thermal sphere-shaped probes located inside the pallets. The aim was to investigate air velocity characteristics above and within pallets. The performance of ventilation was characterized with and without supply air duct systems. Both configurations are extensively used in refrigerated transport. Full-scale measurements were also performed within a load of fruit during transport in a refrigerated truck in order to evaluate the temperature distribution under given operating conditions. The numerical modelling of airflow was performed using the computational fluid dynamics (CFD) fluent code and the Reynolds Stress Model (RSM) turbulence model. Numerical and experimental data make it possible to evaluate the air ventilation levels and their heterogeneity between the pallets. The numerical predictions show reasonable agreement with experimental data. The studied supply air duct system improves significantly the homogeneity of ventilation in the vehicle.

Airflow pattern and temperature distribution in a typical refrigerated truck configuration loaded with pallets

This work is part of a research activity aiming to improve and to optimise air-distribution systems in refrigerated vehicles in order to decrease the temperature differences throughout palletised cargos. This condition is essential in order to preserve the quality, safety and shelf life of perishable products. The present study reports on the numerical and experimental characterization of airflow within a semi-trailer enclosure loaded with pallets. The experiments were carried out on a reduced-scale (1:3.3) model of a refrigerated-vehicle trailer. The performance of ventilation and temperature homogeneity were characterized with and without supply air duct systems. Both configurations are extensively used in refrigerated transport. The numerical modelling of airflow was performed using the Computational Fluid Dynamics (CFD) code Fluent and a second-moment closure, the Reynolds stress model (RSM). The results obtained using the RSM model showed good agreement with the experimental data. Numerical and experimental results clearly show the importance of air ducts in decreasing temperature differences throughout the cargo.

Numerical modelling of airflow over an idealised transverse dune

The general flow structure over transverse aeolian dunes is now well documented through both field studies and wind tunnel experiments. Research on windward (stoss) slopes of dunes is extensive and has recently been complemented by research on the lee-side flow structure. However, a number of technical deficiencies in wind tunnel instrumentation and a lack of detailed resolution in and appropriate turbulence instrumentation for field research have resulted in an incomplete quantified characterisation of the flow structure over aeolian dunes. This study applies a two-dimensional numerical model with an RNG-modified κ- ϵ turbulence model to simulate the time-averaged flow field over an idealized aeolian dune. The model is successfully validated with wind tunnel experimental data. Results indicate that the model accurately predicts the flow patterns over the dune, producing regions of flow stagnation at the toe, acceleration up the stoss slope and a region of flow separation and reversal in the lee. Further development and application of this model will allow examination of flow-form interaction, the testing of more complex isolated dune morphologies, and characterisation of flow over multiple dunes.

Wall air–jet characteristics and airflow patterns within a slot ventilated enclosure

The present study reports on the numerical and experimental characterisation of airflow generated by a wall jet within a long and empty slot-ventilated enclosure. In the configuration investigated, blowing and outlet sections are placed in the front of the box. This design is extensively used in refrigerated transport. Experiments were carried out on a scale model ( 1 :3.3 ) of a trailer. Numerical modelling of airflow was performed using the computational fluid dynamics Fluent code. In this study, a second-moment closure, the Reynolds stress model (RSM) and two-equation turbulence models: the standard k– ε and a renormalization group (RNG), were tested, contrasted and compared with experimental data. It was demonstrated that only the RSM model enabled detection of the presence and the localisation of separated flow and correctly predicts airflow patterns related to primary and secondary recirculation.

Numerical Study of Hybrid Ventilation of Apartments in a Densely-Populated Urban Neighbourhood

The demand for buildings with high quality indoor environments is growing, especially in developing countries, where more and more energy will be consumed in the near future. Air flow pattern, air temperature and humidity are among the main parameters that contribute to indoor thermal comfort. Care must be taken to design the most energy-efficient air distribution system that provides comfort for the occupants. To achieve this it is very helpful to know the air flow patterns and the temperature and humidity field in a building at the design stage.This paper presents results derived from the numerical modelling of air flow and heat and mass transfer within an apartment building in a densely populated urban neighbourhood. Typically, such apartment blocks are in close proximity to each other and cross contamination between apartments in the same and adjacent buildings can occur.As the Reynolds number is large, the air flow is fully turbulent. After validation of the numerical procedure and the turbulence model against benchmark cases, the k- ω turbulence model was employed to evaluate the air flow pattern, temperature, and contaminant concentration in the ground floor and top floor apartments.Based on the numerical results, suggestions are given for the design of hybrid ventilation systems for use in high-rise buildings in densely populated residential regions. For the configuration of shared ventilation shafts, considered in this paper, it is concluded that a built-in fan should be used to control the direction of the air flow and to avoid cross contamination. It is also concluded that this, fan assisted, ventilation system approach provides thermal comfort in a temperature band somewhere above 20°C and below 30°C. This approach it is much cheaper to operate than full air-conditioning.

Numerical and experimental study of airflow in a typical refrigerated truck configuration loaded with pallets

This work is part of a research activity aiming to improve and to optimize air-distribution systems in refrigerated vehicles in order to decrease the temperature differences within the load. The present study reports on the numerical and experimental characterization of airflow generated within a semi-trailer enclosure loaded with pallets. In the studied configuration, inlet and outlet sections were placed in the front of the trailer. This is a very common configuration and is extensively used in refrigerated transport. The experiments were carried out on a reduced-scale model built with a ratio 1/3.3 of a trailer. The numerical modeling of airflow was performed using the computational fluid dynamics (CFD) code Fluent and two levels of turbulence modeling: the standard k– ε model and a model with a second-moment closure, the Reynolds stress model (RSM). Only the results obtained using the RSM model showed agreement with the experimental data.

Numerical Modelling of Air Flow in Air Jet Weaving System

Paper summarizes the first results of two-dimensional (2D) numerically modelled expansion and flow of compressible and non-viscous gas in typical parts of air jet weaving system: in main nozzle designed as an ejector with various shapes of the mixing zone, in relay (auxiliary) nozzle with substantial flow separation in the rash flow bend directly before the nozzle outlet and the influence of the shape of the reed dent edges on the free stream reflection and penetration through reed gaps along a real “porous” wall. Used Euler's equations are solved by a Finite Volumes Method (FVM) with automatic mesh generation and optimization of unstructured triangle mesh. Graphical results show 2D isolines of all state values of the gas, further Mach number, entropy and velocity vectors. ID profiles of all quantities along choosen cross-section or surface can be obtained, too. They give to the designer a large and quick review about the problem. The coincidence with experiment, measuring and real weaving tests is very good. The advantage of the PC using consists in the very quick, simple and user-friendly operation.

Modelling of air flow and cloud fields over the Northern Pennines

Numerical modelling of air flow and the clouds evolving in this air flow are performed to better understand the dynamical and thermodynamical conditions which prevailed during the main observational episodes of the EUROTRAC-ground based cloud experiment 1993 on Great Dun Fell (England). A non-hydrostatic cloud model with two nested model domains of increasing grid resolution is used, to zoom from the mesoscale environment of northern England, into the cloud forming relief of the northern Pennines and finally into the small-scale terrain of the field experiment. The vertical and horizontal extensions of the modelled surface cloud fields are mainly determined by the initial profile of temperature and humidity in the first 1500 m. Initial wind profile and topography also contribute to the structure of the orographic surface clouds. A trajectory analysis for the neighbouring observational points in the field site show that, also on scales of a few kilometres, air parcels with quite different cloud life histories can be expected. Numerical tracer experiments indicate that for the prevailing northeasterly wind conditions SO 2 plumes from the New Castle environment can affect the measuring site. Furthermore, the methods providing the trajectories and streamlines for the chemical and mircophysical evaluations of the experiment by parcel models are presented.

Airflow above changes in surface heat flux, temperature and roughness; an extension to include the stable case

A numerical model of airflow above changes in surface roughness and thermal conditions is extended to include cases with stable thermal stratification within the internal boundary-layer. The model uses a mixing-length approach with empirical forms for φM and φH. Results are presented for some basic cases and an attempt is then made to compare results given by the model with the experimental results of Rider, Philip and Bradley. Tolerable agreement is achieved. The importance of roughness change and thermal stability effects in the diffusion of heat and moisture near a leading edge is emphasised.

A model of airflow above changes in surface heat flux, temperature and roughness for neutral and unstable conditions

A numerical model of airflow in the lowest 50–100 m of the atmosphere above changes in surface roughness and temperature or heat flux has been developed based on boundary layer approximations, the Businger-Dyer hypotheses for the non-dimensional wind shear and heat flux and a mixing length hypothesis.