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[[File:Fig 1 Formation of grid in cfd.JPG|thumb|Fig 1 Formation of grid in cfd]]Almost every [[computational fluid dynamics]] problem is defined under the limits of initial and boundary conditions. When constructing a staggered grid, it is common to implement boundary conditions by adding an extra node across the physical boundary. The nodes just outside the inlet of the system are used to assign the inlet conditions and the physical boundaries can coincide with the [[scalar control]] volume boundaries. This makes it possible to introduce the boundary conditions and achieve discrete equations for nodes near the boundaries with small modifications.▼
}}{{Main|Boundary conditions in fluid dynamics}}▼
▲[[File:Fig 1 Formation of grid in cfd.JPG|thumb|Fig 1 Formation of grid in cfd]]Almost every [[computational fluid dynamics]] problem is defined under the limits of initial and boundary conditions. When constructing a staggered grid, it is common to implement boundary conditions by adding an extra node across the physical boundary. The nodes just outside the inlet of the system are used to assign the inlet conditions and the physical boundaries can coincide with the scalar control volume boundaries. This makes it possible to introduce the boundary conditions and achieve discrete equations for nodes near the boundaries with small modifications.
'''The most common boundary conditions used in [[computational fluid dynamics]] are'''
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==Intake boundary conditions==
Consider the case of an inlet perpendicular to the x direction.
[[File:Fig.4 pressure correction cell at intake boundary.JPG|thumb|Fig.4 pressure correction cell at intake boundary]]▼
*For the first u, v, φ-cell all links to neighboring nodes are active, so there is no need of any modifications to discretion equations.
*At one of the inlet node absolute pressure is fixed and made pressure correction to zero at that node.
*Generally [[computational fluid dynamics]] codes estimate k and ε with approximate formulate based on turbulent intensity between 1 and 6% and length scale
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| [[File:Fig.2 u-velocity cell at intake boundary.JPG|thumb|Fig.2 u-velocity cell at intake boundary|alt=|none]] || [[File:Fig.3 v-velocity cell at intake boundary.JPG|thumb|Fig.3 v-velocity cell at intake boundary|alt=|none]] || [[File:Fig.4 pressure correction cell at intake boundary.JPG|thumb|Fig.4 pressure correction cell at intake boundary|alt=|none]] || [[File:Fig. 5 scalar cell at intake boundary.JPG|thumb|Fig. 5 scalar cell at intake boundary|alt=|none]]
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==Symmetry boundary condition==
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Consider situation solid wall parallel to the x-direction:
'''Assumptions made and relations considered'''-
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*No slip condition: u = v = 0.
*In this we are applying the “wall functions” instead of the mesh points.
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| [[File:Fig.6 u-velocity cell at a physical boundary.JPG|left|thumb|Fig.6 u-velocity cell at a physical boundary]] || [[File:Fig.7 v-cell at physical boundary j=3.JPG|center|thumb|Fig.7 v-cell at physical boundary j=3]] || [[File:Fig.8 v-cell at physical boundary j=NJ.JPG|thumb|Fig.8 v-cell at physical boundary j=NJ]] ||
▲[[File:Fig.
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'''[[Turbulent flow]]''':
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<math> y^+ > 11.63\,</math>.
in the log-law region of a turbulent [[boundary layer]].
'''[[Laminar flow]]''' :
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==Pressure boundary condition==
[[File:Fig.10 p’-cell at an intake boundary.JPG|left|thumb|Fig.10 p’-cell at an intake boundary]]▼
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▲| [[File:Fig.10 p’-cell at an intake boundary.JPG|left|thumb|Fig.10 p’-cell at an intake boundary]] || [[File:Fig. 11 p’-cell at an exit boundary.JPG|thumb|Fig. 11 p’-cell at an exit boundary]]
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These conditions are used when we don’t know the exact details of flow distribution but boundary values of pressure are known
For example: external flows around objects, internal flows with multiple outlets, [[buoyancy]]-driven flows, [[free surface]] flows, etc.
*The pressure corrections are taken zero at the nodes.
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==Exit boundary conditions==
Considering the case of an outlet perpendicular to the x-direction -
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| [[File:Fig.12 A control volume at an exit boundary.JPG|left|thumb|Fig.12 A control volume at an exit boundary]] || [[File:Fig. 13 v-control volume at an exit boundary.JPG|center|thumb|Fig. 13 v-control volume at an exit boundary]] || [[File:Fig. 14 pressure correction cell at an exit boundary.JPG|thumb|Fig. 14 pressure correction cell at an exit boundary]] || [[File:Fig.15 scalar cell at an exit boundary.JPG|left|thumb|Fig.15 scalar cell at an exit boundary]]
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In fully developed flow no changes occurs in flow direction, gradient of all variables except pressure are zero in flow direction
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[[Category:Computational fluid dynamics]]
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