This happens because ANSYS Fluent solves for a modified pressure. More details can be found on Fluent user guide under: “Pressure Inlet Boundary Conditions” If you want to see the hydrostatic pressure distribution, please open Operating Conditions panel from Solution Setup –> Boundary Conditions page, switch on Specified Operating Density option and set the value to 0. This has to be done before running the calculation. When this approach is used, please make sure that the pressure values specified at the boundaries need to include the hydrostatic component as well.