This document discusses different types of boundary conditions in OpenFOAM including: 1) Steady and time-varying boundary conditions such as Dirichlet, Neumann, and Robin conditions. 2) Periodic and symmetry boundary conditions that can be used for repeating geometries. 3) Mixed boundary conditions that are a weighted combination of fixed value and fixed gradient conditions, controlled by a weighting parameter. 4) Direction mixed boundary conditions for vector fields that apply different conditions in different directions using a weighting tensor.

1. Basic Boundary Conditions
in OpenFOAM v2.4
Classification
Steady
Time-
varying
Dirichlet
Neumann
Robin
Not
Implemented
Periodic
Symmetry
fixedValue uniformFixedValue
fixedGradient uniformFixedGradient
zeroGradient
mixed
cyclic
𝜙 𝒙 = 𝑓 𝒙 𝜙 𝒙, 𝑡 = 𝑓 𝒙, 𝑡
𝜕𝜙
𝜕𝒏
𝒙 = 𝑔 𝒙
𝜕𝜙
𝜕𝒏
𝒙, 𝑡 = 𝑔 𝒙, 𝑡
𝜕𝜙
𝜕𝒏
𝒙 = 0
a𝛼 𝒙 𝜙 𝒙
+𝛽 𝒙
𝜕𝜙
𝜕𝒏
𝒙 = ℎ 𝒙
cyclicAMI
mixed BC
mixed fixedValue
fixedGradient
=
+ ×
×w
(1-w)
w
fixedValue
fixedGradient
W = 1
W = 0
mixed
symmetryPlane
symmetryPlane or slip?
𝜕𝜙
𝜕𝒏
𝒙 = 0
Scalar 𝜙 Vector 𝝓
𝝓 𝒙 ∙ 𝒏 = 0,
𝜕𝝓 𝑡
𝜕𝒏
𝒙 = 𝟎
 symmetryPlane is used on
a single and perfectly flat boundary
 slip can be used on curved boundaries
symmetryPlane slip
𝒏
 mixed BC is a combination of
fixedValue and fixedGradient BCs
 A weighting parameter w (0-1) switches
between these types
directionMixed BC
 For vector fields, directionMixed BC
is a combination of fixedValue and
fixedGradient BCs
 A weighting parameter (tensor) controls
which direction these BCs are apply to
1
2
𝒏 ⊗ 𝒏 + 𝒏 ⊗ 𝒏 𝑇
w
𝑂3 (Zero matrix)
𝐼3 (Identity matrix) fixedValue
fixedGradient
fixedGradient
fixedValue
Normal direction
Tangential direction
All directions