Prediction Of Airflow Patterns Research Articles

Modelación CFD de casos básicos de convección en ambientes cerrados: Necesidades de principiantes en CFD para adquirir habilidades y confianza en la modelación CFD

Prediction of airflow pattern and velocities, temperature, moisture and pollutants concentration is required to design healthy and comfortable indoor environments. Computational Fluid Dynamics (CFD) is the most advanced technique to model and predict the airflow in enclosed environments. However, the main errors in CFD models and their results are linked to the human factor. Beginners on CFD modeling do not account with skills, experience and engineering judgment to generate robust and reliable CFD models. This process is not intuitive and new CFD users need guidance. This paper aims to provide more complete information on CFD modeling of basic natural, forced and mixed convection cases that would allow CFD beginners to acquire skills and confidence. CFD modeling includes mesh generation, setting convergence criteria and under-relaxation factors, and evaluating different turbulence models for each convection case. Results show that users´ expertise is needed in each step of CFD modeling, even for these basic convection cases. Rev. ing. constr. [online]. 2014, vol.29, n.1, pp. 22-45. ISSN 0718-5073 http://dx.doi.org/10.4067/S0718-50732014000100002

Prediction of Air Flow Pattern Influenced by Incoming Jet Direction with FEM in Confinement Livestock House

Prediction of Air Flow Pattern Influenced by Incoming Jet Direction with FEM in Confinement Livestock House

Prediction of airflow patterns in a ventilated enclosure with zonal methods

A zonal model with two different approaches for expressing mass flow rates (the conventional method based on relations for flow in conduits and the shear stress QSNA-Newton’s approximation) is used to predict airflow patterns in a ventilated isothermal enclosure. A new proposed 3D wall jet model gives much better agreement with experimental results than the previously available 2D wall jet model. The outlet boundary condition ( m ˙ out = m ˙ in or P out = P atm) has no influence on the mass flow rates. However, the pressure condition should be chosen when there is more than one outlet. Based on the calculated results, it is recommended that the shear stress approximation should be privileged over the conventional method since the latter predicts completely unrealistic average cell pressures with both outlet boundary conditions.

Study of Parameters Affecting Cooling Rate and Temperature Distribution in Forced-air Precooling of Strawberry

In this work, the cooling rate and temperature distribution during forced-air precooling of strawberries were studied using different packaging designs. Experimental cooling times were obtained for five selected cup designs including the standard thermoformed cup at three different airflow rates (2, 3, and 4 L/s-kg). A reduction of 30 to 44% of the 7/8 cooling time (T7/8) was observed when increasing the airflow rate from 2 to 4 L/s-kg. The vent design of the standard flat allowed air to flow directly to the second cup without cooling effectively the first cup. Modified flats which allow air to flow freely through the cups can decrease the T7/8 cooling time. The modified cup had an improved cooling efficiency of 51% better than the standard thermoformed cup used by Quebecs grower. This cup combined with the modified flat reduced the T7/8 cooling time by up to 41% when compared to the wire mesh basket-standard flat widely used in the United States. Future research will be conducted on the prediction of airflow patterns by finite elements to improve the cooling efficiency of forced-air cooling for horticultural products.

The prediction of airflow patterns in livestock buildings

The pattern of air movement in a livestock building forms the link between the ventilation system and the microclimate round the stock. In order to study first the airflow pattern and secondly the resulting microclimate, a full scale section of a typical intensive livestock building with a transparent gable end was built within a controlled temperature enclosure. This paper shows the principal factors governing airflow patterns and derives qualitative rules whereby the pattern of air movement may be predicted. It is shown (a) that air moves in a series of rotary motions produced by obstacles in the path of the incoming air stream and by convection currents from stock; (b) that with jet ventilation the design of the inlet has a dominant effect whilst the outlet has a minimal effect and (c) that the concept of “summer” ventilation and “winter” ventilation is often misleading.

Effects due to groups of buildings

For the past 5-10 years architects have realized the need for information on the aerodynamics of the environment around groups of buildings. The high wind speeds in precincts around tall or exposed buildings have surprised their designers who have sought remedies, and the publicity about windy environments around existing buildings has led to requests for advice about developments on the drawing board. In the absence of a general theory for the prediction of air flow patterns and wind speeds around groups of buildings, the problem has been studied in wind tunnels. The paper describes typical town centre developments in which a problem of wind environment has arisen, and gives a brief account of the investigation of specific cases. The broad conclusions from some twenty case studies made by the Building Research Station in response to inquiries from industry are summarized. In seeking to generalize, a series of investigations of the air flow around small groups of idealized model buildings has been conducted, and some comparisons between model and full-scale measurements have been made. This has led to a design method for use in planning the layout of small groups of buildings, which draws on the data from model tests and also meteorological information and comfort criteria. This work is outlined, and future research needs are also discussed.