Ansys Fluent: how the sign of wall shear stress determines the fluid flow direction
Hello, I was confused by the sign of wall shear stress and velocity direction.
Initially, i thought if I want to force the fluid flow in zdirection, i should also set a positive shear stress. However, I found the sign of shear stress and velocity is always oopsite in Ansys Fluent
Answers

When i set a negative zcomponent shear stress of 1Pa, the z velocity had a positive direction, which indicates a opposite direction.
[Specified Shear manual:
In addition to the noslip wall that is the default for viscous flows, you can model a slip wall by specifying zero or nonzero shear. For nonzero shear, the shear to be specified is the shear at the wall by the fluid. To specify the shear, select the Specified Shear option under Shear Condition (see Figure 7.3.16).]0