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Click to edit Master text styles,Second Level,Third Level,Fourth Level,Fifth Level,title style,Fluent Inc.,*,4-,*,Introductory,FLUENT,Notes,FLUENT v6.0 Jan 2002,Fluent User Services Center,Boundary Conditions,Defining Boundary Conditions,To define a problem that results in a,unique,solution,you must specify information on the dependent(flow)variables at the domain boundaries.,Specifying fluxes of mass,momentum,energy,etc.into domain.,Defining boundary conditions involves:,identifying the location of the boundaries(e.g.,inlets,walls,symmetry),supplying information at the boundaries,The data required at a boundary depends upon the boundary condition,type,and the physical models employed.,You must be aware of the information that is required of the boundary condition and locate the boundaries where the information on the flow variables,are known or can be reasonably approximated,.,Poorly defined boundary conditions can have a significant impact on your solution.,Fuel,Air,Combustor Wall,Manifold box,1,1,2,3,Nozzle,Locating Boundaries:Example,Three possible approaches in locating inlet boundaries:,1.Upstream of manifold,Can use uniform profile,Properly accounts for mixing,Non-premixed reaction models,Requires more cells,2.Nozzle inlet plane,Non-premixed reaction models,Requires accurate profile data,3.Nozzle outlet plane,Premixed reaction model,Requires accurate profile,General Guidelines,General guidelines:,If possible,select boundary location and shape such that flow either goes in or out.,Not necessary,but will typically observe better convergence.,Should not observe large gradients in direction normal to boundary.,Indicates incorrect set-up.,Minimize grid skewness near boundary.,Introduces error early in calculation.,2,1,Upper pressure boundary modified to ensure that flow always enters domain.,Available Boundary Condition Types,Boundary Condition Types of,External Faces,General,:Pressure inlet,Pressure outlet,Incompressible,:Velocity inlet,Outflow,Compressible flows,:Mass flow inlet,Pressure far-field,Special,:Inlet vent,outlet vent,intake fan,exhaust fan,Other,:Wall,Symmetry,Periodic,Axis,Boundary Condition Types of,Cell Boundaries,Fluid and Solid,Boundary Condition Types of,Double-Sided Face Boundaries,Fan,Interior,Porous Jump,Radiator,Walls,inlet,outlet,wall,interior,Orifice_plate and orifice_plate-shadow,Changing Boundary Condition Types,Zones and zone types are initially defined in pre-processor.,To change zone type for a particular zone:,Define,Boundary Conditions.,Choose the zone in,Zone,list.,Can also select boundary zone using right mouse button in Display Grid window.,Select new zone type in,Type,list.,Setting Boundary Condition Data,Explicitly assign data in BC panels.,To set boundary conditions for particular zone:,Choose the zone in,Zone,list.,Click,Set,.button,Boundary condition data can be copied from one zone to another.,Boundary condition data can be stored and retrieved from file.,file,write-bc and,file,read-bc,Boundary conditions can also be defined by UDFs and Profiles.,Profiles can be generated by:,Writing a profile from another CFD simulation,Creating an appropriately formatted text file with boundary condition data.,Velocity Inlet,Specify Velocity by:,Magnitude,Normal to Boundary,Components,Magnitude and Direction,Velocity profile is uniform by default,Intended for incompressible flows.,Static pressure adjusts to accommodate prescribed velocity distribution.,Total(stagnation)properties of flow also varies.,Using in compressible flows can lead to non-physical results.,Can be used as an outlet by specifying negative velocity.,You must ensure that mass conservation is satisfied if multiple inlets are used.,Pressure Inlet(1),Specify:,Total,Gauge,Pressure,Defines energy to drive flow.,Doubles as back pressure(static gauge)for cases where back flow occurs.,Direction of back flow determined from interior solution.,Static,Gauge,Pressure,Static pressure where flow is locally supersonic;ignored if subsonic,Will be used if flow field is initialized from this boundary.,Total Temperature,Used as static temperature for incompressible flow.,Inlet Flow Direction,Incompressible flows:,Compressible flows:,Pressure Inlet(2),Note:Gauge pressure inputs are required.,Operating pressure input is set under:Define Operating Conditions,Suitable for compressible and incompressible flows.,Pressure inlet boundary is treated as loss-free transition from stagnation to inlet conditions.,Fluent calculates static pressure and velocity at inlet,Mass flux through boundary varies depending on interior solution and specified flow direction.,Can be used as a“free boundary in an external or unconfined flow.,Mass Flow Inlet,Specify:,(a)Mass Flow Rate or(b)Mass Flux,(a)implies uniform mass flux,(b)can be defined by profiles/UDF,Static,Gauge,Pressure,Static pressure where flow is locallysupersonic;ignored if subsonic,Will be used if flow field is initialized from this boundary.,Total Temperature,Used as static temperature for
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