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Forecasting roof snow accumulation using numerical models
JOURNAL OF
ELSEVIER
Journal of Wind Engineering and Industrial Aerodynamics 67&68 (1997) 938,939
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Forecasting roof snow accumulation using numerical models A. B a s k a r a n a, A. K a s h e f Building Performance Laboratory, Institute Jbr Research in Construction, National Research Council Canada, Ottawa, Ont., Canada K1A OR6
Abstract
To forecast snow accumulation rate on large roofs, the present study used the Computational Fluid Dynamics (CFD) tools and techniques. A numerical model is formulated using the 3D Navier-Stokes Equations (NSE) together with the standard k-e turbulence model. For the model development, the control volume technique is employed to discretize the differential equations into difference form and the developed model has been used to simulate the air flow predictions over variety of roof configurations. To assess the snow-drift condition for each configuration, the velocity components are extracted from the simulated air flow results and the local wind speeds are calculated at different locations. The threshold values of snow particles are calculated for three different types of snow fall: light, medium, and heavy. A comparison of the calculated wind speed with the threshold value determines whether a snow-drift process will take place. Comparing the local wind speed and the threshold value for each type of snow, the forecast for the possibility of snow accumulation is presented by "Yes" or "No". This has been performed for a flat roof building configuration of about 112 m long, 24 m wide and 12 m high. For this unusual building aspect ratios (5 and 10 respectively for length/width and length/height), local wind environmental conditions are evaluated and snow accumulations are forecasted. The model has been extended not only to include complex roof configurations but also to quantify the snow accumulation on roofs for a given ground snow fall. Modeled configurations are: a three level slope roof (15 c, 5 and 5 °) and a 13 '~ slope roof with two levels. Both roofs envelop a building of about 63 m long, 57 m wide and 13 m high. Architectural features such as parapets can significantly modify the local wind flow conditions over a roof. Effect of small architectural features of about 1 m height on these large roofs are also predicted based on the developed model. Combining the present investigation with the theories developed based on experimental work, a general procedure to compute snow accumulation has been developed and it
1 E-mail: [email protected].
0167-6105/97/$17.00 ~. 1997 Published by ElsevierScienceB.V. All rights reserved. P I I S01 67-6 1 05(97)001 34-7
A. Baskaran, A. Kashef/J. Wind Eng. Ind. Aerodyn. 67&68 (1997) 938, 939
939
involves the following steps: 1. calculation of the wind environmental conditions to obtain the friction velocity at each nodal point, 2. determination of snow transport rate, 3. estimation of erosion or deposition rates The simplified procedure is used to quantify snow accumulations for variety of configurations derived by modifying the three level roof geometry. Efforts are also made to quantify the validity of model predictions through comparisons with field observation. The above evaluations demonstrate that the CFD techniques can be effectively applied during the early stage of the design process as a predictive tool in forecasting snow accumulation on various roof configurations.
ELSEVIER
Journal of Wind Engineering and Industrial Aerodynamics 67&68 (1997) 938,939
_ ~ ~ i ~
Forecasting roof snow accumulation using numerical models A. B a s k a r a n a, A. K a s h e f Building Performance Laboratory, Institute Jbr Research in Construction, National Research Council Canada, Ottawa, Ont., Canada K1A OR6
Abstract
To forecast snow accumulation rate on large roofs, the present study used the Computational Fluid Dynamics (CFD) tools and techniques. A numerical model is formulated using the 3D Navier-Stokes Equations (NSE) together with the standard k-e turbulence model. For the model development, the control volume technique is employed to discretize the differential equations into difference form and the developed model has been used to simulate the air flow predictions over variety of roof configurations. To assess the snow-drift condition for each configuration, the velocity components are extracted from the simulated air flow results and the local wind speeds are calculated at different locations. The threshold values of snow particles are calculated for three different types of snow fall: light, medium, and heavy. A comparison of the calculated wind speed with the threshold value determines whether a snow-drift process will take place. Comparing the local wind speed and the threshold value for each type of snow, the forecast for the possibility of snow accumulation is presented by "Yes" or "No". This has been performed for a flat roof building configuration of about 112 m long, 24 m wide and 12 m high. For this unusual building aspect ratios (5 and 10 respectively for length/width and length/height), local wind environmental conditions are evaluated and snow accumulations are forecasted. The model has been extended not only to include complex roof configurations but also to quantify the snow accumulation on roofs for a given ground snow fall. Modeled configurations are: a three level slope roof (15 c, 5 and 5 °) and a 13 '~ slope roof with two levels. Both roofs envelop a building of about 63 m long, 57 m wide and 13 m high. Architectural features such as parapets can significantly modify the local wind flow conditions over a roof. Effect of small architectural features of about 1 m height on these large roofs are also predicted based on the developed model. Combining the present investigation with the theories developed based on experimental work, a general procedure to compute snow accumulation has been developed and it
1 E-mail: [email protected].
0167-6105/97/$17.00 ~. 1997 Published by ElsevierScienceB.V. All rights reserved. P I I S01 67-6 1 05(97)001 34-7
A. Baskaran, A. Kashef/J. Wind Eng. Ind. Aerodyn. 67&68 (1997) 938, 939
939
involves the following steps: 1. calculation of the wind environmental conditions to obtain the friction velocity at each nodal point, 2. determination of snow transport rate, 3. estimation of erosion or deposition rates The simplified procedure is used to quantify snow accumulations for variety of configurations derived by modifying the three level roof geometry. Efforts are also made to quantify the validity of model predictions through comparisons with field observation. The above evaluations demonstrate that the CFD techniques can be effectively applied during the early stage of the design process as a predictive tool in forecasting snow accumulation on various roof configurations.