Before we apply the NS equation, let us make a note that the NS equation is a 2nd order PDE. Therefore, 2 BCs are required for along each direction to solve for the velocity-field. We should note the common boundary conditions:
No slip condition at the solid surface: it is an experimental observation that the relative velocity at the surface is zero. So, at a stationary solid surface
At the interface of liquid-gas or liquid–liquid (immiscible fluids), there is no jump in the velocity, shear stress and pressure
(Fig. 16a)
(gradients maybe different)
Symmetric BC:
At the center- line of tube or rectangular channel, velocity- gradient is zero.
along each direction to solve for the velocity-field. We should note the common boundary conditions:
at a stationary solid surface
