Calculation Of Air Flow Research Articles

253 案内翼形式軸流サイクロン内の気流及び粒子挙動の計算(流体工学)

253 案内翼形式軸流サイクロン内の気流及び粒子挙動の計算(流体工学)

Monitoring and Modelling Indoor Air Quality and Ventilation in Classrooms within a Purpose-Designed Naturally Ventilated School

This paper investigates the performance in use of thermal passive ventilation stacks in the classrooms of a school during the summer period. Measurements of air temperature, carbon dioxide (CO₂) and air velocity were carried out from which ventilation rates in the classrooms and stacks were calculated. It was found that the airflow through the passive stacks was a significant proportion of the classroom air exchange rate and metabolic CO₂ was lower in classrooms with passive stacks. The predictions of a multi-zone airflow computer model were compared with measured values. Multi-zone modelling indicated that passive stacks could significantly increase ventilation in classrooms, which would otherwise be ventilated via single side ventilation through openable windows on one external wall. It was found that if the zones are accurately represented, multi-zone modelling is able to provide a good indication of the general trends of airflow rates both for the whole classroom and the flow through passive stacks.

Large-eddy simulation of turbulent airflow over complex terrain

In order to develop an overall efficient and accurate method of predicting an unsteady three-dimensional airflow over a complex terrain with characteristic length scales on the order of kilometers, we recently developed the CFD codes referred to as the RIAM-COMPACT ( R esearch I nstitute for A pplied M echanics, Kyushu University, Com putational P rediction of A irflow over C omplex T errain). In this paper, we carried out the calculation of turbulent airflow over a real complex terrain in a horizontal region of 9.5 km×5 km with a relatively fine spatial resolution of 50 m. This area covers the new campus of Kyushu University. In order to generate instantaneous velocity fluctuations in an approaching flow, an unsteady flow field in the driver unit is directly calculated. The numerical results obtained by RIAM-COMPACT demonstrated that the changes induced on the wind field by the topographic effect, such as the local wind acceleration and the flow separation, were successfully simulated. We emphasized the following features as regards the wind field over the new campus area under the influence of the west wind. The wind field in the central region of the new campus area is strongly influenced by the wake region generated behind Mt. Hiyama (244 m). The airflows moving around the side of Mt. Hiyama exhibit relatively small fluctuations. When these winds reach Mt. Ishigateke (99 m), they are locally accelerated at the peak. Consequently, a local speed-up effect is confirmed in the southern part of the new campus area.

Monitoring and Modelling Indoor Air Quality and Ventilation in Classrooms within a Purpose-Designed Naturally Ventilated School

This paper investigates the performance in use of ther mal passive ventilation stacks in the classrooms of a school during the summer period. Measurements of air temperature, carbon dioxide (CO2) and air velocity were carried out from which ventilation rates in the class rooms and stacks were calculated. It was found that the airflow through the passive stacks was a significant pro portion of the classroom air exchange rate and metabolic CO2 was lower in classrooms with passive stacks. The predictions of a multi-zone airflow computer model were compared with measured values. Multi-zone modelling indicated that passive stacks could significantly increase ventilation in classrooms, which would otherwise be ventilated via single side ventilation through openable windows on one external wall. It was found that if the zones are accurately represented, multi-zone modelling is able to provide a good indication of the general trends of airflow rates both for the whole classroom and the flow through passive stacks.

Spurious Numerical Solutions in Coupled Natural Ventilation and Thermal Analyses

It is well known that iterative solution processes can lead to divergence when dealing with coupled airflow and thermal analyses for buildings ventilated either naturally or by a mixed-mode system. The Newton- Raphson method or its variants are used in almost all existing multi-zone airflow models. This paper discusses the qualitative features of the iterative solution processes of the Newton-Raphson method when used for coupled thermal and ventilation analyses of a simple one-zone building with two openings. Chaotic solutions are obtained for three different coupling strategies in combining the airflow and indoor air temperature calculations. The spurious solutions obtained in this paper are due to the inherent characteristics of the Newton-Raphson method. Our analyses on these spurious numerical solutions are based on a simple dynamical systems approach. Unfortunately, there seems to be no general approach to distinguish the true steady-state solution from the spurious numerical solutions in practical simulations. The fact that chaotic solutions were obtained for a very simple problem in this paper may indicate the need for a further understanding of its implications to more complex multi-zone problems. The findings in this paper may serve as a tool for further development of effective numerical methods for multi-zone airflows and may also provide useful knowledge for interpreting the divergence behaviours of some of the numerical simulations in building ventilation.

G109 低温サウナ室内の伝熱と熱流動(オーガナイズドセッション19 : 生体・医療・食品などに関わる複雑輸送現象とその実践的問題)

Experimental and calculated investigation on heat transfer in a low temperature sauna was made. Low temperature sauna was usually heated up by a radiation panel heater at the ceiling to 50 degree C. In order to examine how heat transfers from the radiation heater to a human body in a sauna room, temperature and velocity distribution air were examined by the experiment and calculation of indoor air flow. It was found that heat flowed from the radiation heater to the human body mainly through air convection and wall radiation, not direct radiation from the heater.

Computation of water and air flow with submerged hydrofoil by interface capturing method

Free-surface flows with an arbitrary deformation, induced by a submerged hydrofoil, are simulated numerically, considering two-fluid flows of both water and air. The computation is performed by a finite volume method using unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cellwise local mesh refinement. The integration in space is of second order, based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels. The linear equations are solved by conjugate gradient type solvers, and the non-linearity of equations is accounted for through Picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations, the continuity equation, the conservation equation of one species, and the equations for two turbulence quantities. Finally, a comparison is quantitatively made at the same speed between the computation and experiment in which the grid sensitivity is numerically checked.

00/00477 Building ventilation: a pressure airflow model computer generation and elements of validation

The calculation of airflows is of great importance for detailed building thermal simulation computer codes, these airflows most frequently constituting an important thermal coupling between the building and the outside on one hand, and the different thermal zones on the other. The driving effects of air movement, which are the wind and the thermal buoyancy, are briefly outlined and we look closely at their coupling in the case of buildings, by exploring the difficulties associated with large openings. Some numerical problems tied to the resolving of the non-linear system established are also covered. Part of a detailled simulation software (CODYRUN), the numerical implementation of this airflow model is explained, insisting on data organization and processing allowing the calculation of the airflows. Comparisons are then made between the model results and in one hand analytical expressions and in another and experimental measurements in case of a collective dwelling.

Aeolian processes across transverse dunes. II: modelling the sediment transport and profile development

This paper discusses a model which simulates dune development resulting from aeolian saltation transport. The model was developed for application to coastal foredunes, but is also applicable to sandy deserts with transverse dunes. Sediment transport is calculated using published deterministic and empirical relationships, describing the influence of meteorological conditions, topography, sediment characteristics and vegetation. A so-called adaptation length is incorporated to calculate the development of transport equilibrium along the profile. Changes in topography are derived from the predicted transport, using the continuity equation. Vegetation height is incorporated in the model as a dynamic variable. Vegetation can be buried during transport events, which results in important changes in the sediment transport rates. The sediment transport model is dynamically linked to a second-order closure air flow model, which predicts friction velocities over the profile, influenced by topography and surface roughness. Modelling results are shown for (a) the growth and migration of bare, initially sine-shaped dunes, and (b) dune building on a partly vegetated and initially flat surface. Results show that the bare symmetrical dunes change into asymmetric shapes with a slipface on the lee side. This result could only be achieved in combination with the secondorder closure model for the calculation of air flow. The simulations with the partly vegetated surfaces reveal that the resulting dune morphology strongly depends on the value of the adaptation length parameter and on the vegetation height. The latter result implies that the dynamical interaction between aeolian activity and vegetation (reaction to burial, growth rates) is highly relevant in dune geomorphology and deserves much attention in future studies. Copyright © 1999 John Wiley & Sons, Ltd.

Building ventilation: a pressure airflow model computer generation and elements of validation

The calculation of airflows is of great importance for detailed building thermal simulation computer codes, these airflows most frequently constituting an important thermal coupling between the building and the outside on one hand, and the different thermal zones on the other. The driving effects of air movement, which are the wind and the thermal buoyancy, are briefly outlined and we look closely at their coupling in the case of buildings, by exploring the difficulties associated with large openings. Some numerical problems tied to the resolving of the non-linear system established are also covered. Part of a detailed simulation software ( Codyrun), the numerical implementation of this airflow model is explained, insisting on data organization and processing allowing the calculation of the airflows. Comparisons are then made between the model results and in one hand analytical expressions and in another and experimental measurements in case of a collective dwelling.

NASAL AIRFLOW MEASUREMENT IN NORMAL SUBJECTS BY USING ARABIC WORD PHONETICS

Arabic letters' phonetics can be divided, from the point of view of nasal airflow, into nasal and non-nasar phonemes. Practical measurements have been carried out to define some nasal and non-nasal words. Two sets of words (nasal and non-nasal) have been selected. A pecial software package to achieve the required measurement is written in Turbo Pascal. In this software, the end-point detection is used to recognize the silence from the sound. This is used to enhance the calculation of airflow during each word. Measurements have been performed over 50 nonnal subjects. The results have been processed to define the range of airflow in each word. These ranges are proposed to be the standardization of the method to he used later with the abnormalities. The system used in the measurement is the nasal anemometer. This system is an achievement of a research project financed by the Egyptian Army. The anemometer and the software is an objective (human independent) tool for the diagnosis of nasal airways.

室・ダクト系の空気調和シミュレーションに関する研究

In design for air conditioning equipment, it is important to grasp in advance whether exhibit equipment's design abilities or not. So, we take up rooms and ducts system in air conditioning equipment, and apply to estimate calculation of room pressure and airflow for room other than clean room. This paper refers to make clear various characteristics of control, at the same time to make an estimate of room pressure and airflow by simulation. Parameters of the subject are heat characteristics of rooms, air temperature and humidity, special quality of control and wind environment.

Coupled vibration-dissociation-exchange reactions model for hypersonic airflow computations

Coupled vibration-dissociation-exchange reactions model for hypersonic airflow computations

Solving Air Flows in Mushroom-Growingrooms

Long convergence times in the calculation of air flow for mushroom-growing rooms prompted the extension of the Coupled Equations Line Solver (CELS) method to three dimensions. Initial results were encouraging. When tested on a turbulent flow in an empty domain best results gave greater than 70% reduction in convergence time. An important feature of air flows in mushroom growing rooms is the presence of obstructions. While straightforward under the original solver, CELS presented difficulties in this type of calculation. The associated Additive Correction Multigrid technique was also extended to three dimensions but no useful savings were made.

Un modèle simplifié pour la prédiction du champ de température dans les bâtiments

This study presents a zonal model for predicting the air temperature distribution in buildings. This model is unique in the calculation of mass air flows between two zones. To do so, we distinguish zones where the momentum is small and for which we calculate the flow rates with the aid of a pressure field, and the driving zones described using appropriate specific flow laws. To better understand the consistency of the model, we used experimental results obtained with a one and then a two zone test cell and an experimental atrium with various thermal conditions. A comparison between computed and measured air temperature distributions proves that the model gives a satisfactory prediction of the physical phenomena. This allows us to consider the integration of this type of model into a thermal multizone building code in relation with thermal comfort, energy consumption and indoor air quality.

Prediction of air temperature distribution in buildings with a zonal model

This study presents a zonal model used for predicting the air temperature distribution inside a room. This model is original in the calculation of mass air flows between two zones. To do so, we distinguish zones where the momentum is small and for which we calculate the flow rates with the aid of a pressure field, and the driving zones described using appropriate specific flow laws. A comparison between experimental results and those obtained with the model proves that they are fully consistent with each other. This allows us to consider the integration of this type of model into a general building thermal code.

Intergranular Air Movement and Grain Drying in Silos with Fully, Partially and Slanted Perforated Floor

ABSTRACT Intergranular air movement and its relation with moving drying fmnt in a grain bulk were investigated experimentally. An improved computer simulation model was developed to analyze the drying or cooling process in a bed of grain with non-parallel airflow from a partially or slanted perforated floor. The model first simulates the airflow, then calc lates the heat and mass transfer between air and grain along the airflow streamlines. The results were compared with the simulated and experimental results from a fully perforated floor configuration. The degree of agreement between the computed and the experimental moisture contents depended upon the floor configuration. The model was not capable of predicting the temperatures to the accuracy of the predicted moisture contents, especially when airflow stream lines were not parallel to each other. For further improvement of the drying simulation model, an improved airflow model and computer program is required. Comparison of the simulated results with e...

The Significance of Particle Deposition Patterns in Bronchial Airway Bifurcations for Extrapolation Modeling

ABSTRACT The validity of extrapolating rat deposition data to human inhalation conditions depends on the degree of similarity (or difference) of their particle deposition patterns. Statistical analyses of human and rat tracheobronchial morphometry data have revealed distinct asymmetric features of their airway branching patterns, particularly for the monopodial branching structure of the rat lung. Our predictions of particle deposition patterns within asymmetric bronchial bifurcations in human and rat lungs are based on a numerical model for the calculation of airflow and aerosol particle trajectories in three-dimensional asymmetric bifurcation models: (i) the Navier-Stokes equations for the air velocity field are solved by a finite difference volume method, and (ii) trajectories of aerosol particles entrained in the airstream are simulated by Monte Carlo techniques. In the present paper, the effects of interspecies differences in particle deposition patterns are explored for two typical bifurcation geome...

Verallgemeinerung der Stromfunktionsmethode auf drei Dimensionen

It is shown that the stream-function method, which is dedicated to the solution of two-dimensional incompressible flow problems, can be generalized to three dimensions in a natural way. The main feature of the new method is that only two stream-function components are needed. After analytical considerations a numerical model for the calculation of air flow around buildings is presented which is based on the generalized method. The results of some test simulations show the practical applicability of the method

Coupling of thermal and airflow calculation programs offering simultaneous thermal and airflow analysis

This paper assesses the feasibility of coupling a thermal simulation sofware (Apache†) with a multi-zone airflow software (Swifib†). The simultaneous multi-zone airflow and thermal analysis is particularly important in large enclosure buildings, such as atria. The study highlights the need for such analysis and shows that a new generation of combined thermal and airflow software can be produced by coupling the currently available thermal and airflow simulation software together. The combined software provides the design engineers with a fast, effective and computationally less demanding tool for analysing the performance of the built environment.