Boundary conditions in computational fluid dynamics: Difference between revisions

Revision as of 11:26, 7 December 2012

Revision as of 12:23, 8 December 2012

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{{Orphan|date=December 2012}}

[[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. For implementation of boundary conditions when we construct a staggered grid we add an extra node across the physical boundary in order to get,

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*pressure conditions

*exit conditions

==Intake boundary conditions==

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[[File:Fig.3 v-velocity cell at intake boundary.JPG|center|thumb|Fig.3 v-velocity cell at intake boundary]]

[[File:Fig. 5 scalar cell at intake boundary.JPG|left|thumb|Fig. 5 scalar 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.

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*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

==Symmetry boundary condition==

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*High Reynolds number

*No chemical reactions at the wall

==cyclic boundary condition==

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*Values of each variable at the nodes at upstream and downstream of the inlet of the inlet plane are equal to values at the nodes at upstream and downstream of the outlet plane.

==Pressure boundary condition==

[[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]]

These conditions are used when we don’t know the exact details of flow distribution but boundary values of pressure are know

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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.

==exit boundary conditions==

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[[File:Fig. 13 v-control volume at an exit boundary.JPG|center|thumb|Fig. 13 v-control volume at an exit boundary]]

[[File:Fig.15 scalar cell at an exit boundary.JPG|left|thumb|Fig.15 scalar cell at an exit boundary]]

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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<math>U_{NI,J} = U_{NI-1,J}\frac{M_{in}}{M_{out}}\,</math>.

==References==

<references/>

*An introduction to computational fluid dynamics by Versteeg,PEARSON.

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