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MIT 4 411 - Study Guide

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CFD Applications in Building Design and PlanningJinchao YuanApril 7th, 2004Outline• BackgroundWhat, why, and how• Indoor ApplicationsBalcony Case• Outdoor ApplicationsFlow around building• ConclusionWhat is CFD?• Computational Fluid Dynamics• Divide a space into fine cells• Predict the fluid motion under certain boundary conditionsWhat does CFD do?• Airflow Distribution• Temperature profile• Contaminant Transport• Thermal comfortWhy using CFD?Existing methods to study fluid dynamics:• Analytical or simple empirical modelsNot applicable for complex problems• Full or reduced scale model ExperimentsExpensive, time consuming• Numerical Methods (CFD)Inexpensive, fastHow does CFD work?• Geometry input• Boundary condition• Preprocessing• Calculation• Post processingBalcony CaseGeometry – Calculation DomainGeometry – Interior LayoutBoundary Conditions - Wind• Wind direction0 incident angle• Wind velocity2.0 m/s•Outletmass conservationBoundary Conditions – Thermal• AdiabaticWall, Floor, Ceiling• Heat sourceHuman, Computer• Surface temperatureWallNumerical Settings• Initial guess value• Iteration control• Relaxation control• Output selectionResult – Velocity (Aerial)Result – Velocity (Interior)Result – Flow VisualizationResult – TemperatureOutdoor AirflowOutdoor Comfort ConceptBeaufort No. Description Wind Velocity (m/s)Wind Effect2 Light breeze 1.6-3.3 Wind felt on face3 Gentle breeze 3.4-5.4 Hair disturbed4 Moderate breeze 5.5-7.9 Raise dust and loose paper5 Fresh breeze 8.0-10.7 Wind force felt by body6 Strong breeze 10.8-13.8 Umbrellas used with difficulty7 Near gale 13.9-17.1 Inconvenience felt when walking8 Gale 17.2-20.7 Generally impedes progress9 Strong Gale 20.8-24.4People blown overCase - LanqiyingCalculation Domain• Includingall the buildings• 3 times in width and length• 5 times in heightdirectionBoundary Conditions - Wind Direction• Whether data in Beijing 1960-1990• Wind Rose• Fall & Winter – North and Northwest Average velocity 3m/s, frequent 5m/s• Spring & Summer – South and Southwest Average velocity 5.5m/sBoundary conditions – Windprofileh>380m28.0¸¸¹·¨¨©§ ggZZUUZ10mU5m/sNorth Wind (1.5m above the ground)Northwest wind, 1.5mVertical DistributionConclusion• CFD is a fast and reliable tool for building analysis• CFD can predict parameters such as Flow, temperature, CO2 concentration in great details• CFD can be widely used to guide ventilation system design and building planning.The

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