Boundary conditions in fluid dynamics are the set of constraints to boundary value problems in computational fluid dynamics. These boundary conditions include inlet boundary conditions, outlet boundary conditions, wall boundary conditions, constant pressure boundary conditions, axisymmetric boundary conditions, symmetric boundary conditions, and periodic or cyclic boundary conditions.  
Transient problems require one more thing i.e., initial conditions where initial values of flow variables are specified at nodes in the flow domain. Various types of boundary conditions are used in CFD for different conditions and purposes and are discussed as follows.