Normal Stress Boundary Condition
The total stress on the boundary is set equal to a stress vector of magnitude
f
0
, oriented in the negative normal direction:
using the compressible/weakly compressible and the incompressible formulation, respectively.
This implies that the total stress in the tangential direction is zero. This boundary condition implicitly sets a constraint on the pressure which for 2D flows is
(4-38)
If
∂
u
n
/∂
n
is small,
Equation 4-38
states that
p
≈
f
0
.
The Normal Stress condition is the mathematically correct version of the
Pressure Conditions
condition (
Ref. 4
), but it is numerically less stable.
