Boundary conditions in computational fluid dynamics: Difference between revisions

Revision as of 17:12, 10 December 2014

Revision as of 22:12, 17 May 2016

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[[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.

*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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*The near wall flow is considered as [[laminar]] and the velocity varies linearly with distance from the wall

*No slip condition: u = v = 0.

*In this we are applying the “wall functions” instead of the mesh points.

'''[[Turbulent flow]]''':

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*High [[Reynolds number]]

*No chemical reactions at the wall

==cyclic boundary condition==

*We take flux of flow leaving the outlet cycle boundary equal to the flux entering the inlet cycle boundary

*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.

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[[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

The equations are solved for cells up to NI-1, outside the ___domain values of flow variables are determined by extrapolation from the interior by assuming zero gradients at the outlet plane

The outlet plane velocities with the [[Continuity (mathematics)|continuity]] correction

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

==References==