As far as I know, usually SIMPLE-related codes assume a initial pressure value when users give a velocity-inlet and outflow boundary condition. In this case, only pressure drop in system is meaningful.

So, how does FLUENT(including any SIMPLE-related codes) deal with the pressure boundary condition? At first, I thought "calculated flow field is not an absolute value because there is no information of continuity." However, in FLUENT manual, they say the code uses a initial velocity value from Bernoulli's Equation. Someones told me in case of pressure boundary problem, velocity value is one of the possible solutions.

Can anyone give me an advice?

I would appreciate your detailed explanation.

(1). Try to solve a very simple flow through a duct. (2). Try to follow the sample problem, if there is one available. (3). Try to get the solution from the sample tutrial problem. (3). Then, change the inlet, outlet boundary conditions, step-by-step, and check the solutions. (4). It is not important how the code is written or the boundary conditions are specified. The important thing is to know how each option will give what solution.