CFD turbulent fluid, discussion about pressure gradient

[Royni Abud]

I simulated an incompressible turbulent flow across a tube. I managed to solve it using OpenFoam and the results seem to be right. However, I noted some vacuum pressure after the sudden expansion but can't figure out why the pressure decreases and then increases again. According to Bernoulli's equation, the pressure should increase as the velocity decrease. Could someone explain me why? Below are some details.

inlet velocity = 10 m/s
inlet pressure = 0 (gauge)
turbulent model used k-epsilon
kinematic viscosity = 1*10^-5 m2/s
Here are pressure field and velocity field respectively:

 

[Navin A S]

The decrease in pressure after the sudden expansion is due to the loss of kinetic energy associated with the rapid decrease in velocity. This decrease in velocity causes a decrease in pressure as per Bernoulli's equation. As the flow continues, the velocity and pressure increase again due to the turbulent mixing of the flow, which helps to recover some of the lost kinetic energy. The pressure then increases again until it reaches its original value at the outlet.