Pressure Reduction in Diffuser Outlet
 

Hello,

I am simulating an air flow in a diverging open channel at a Mach Number of 0.15. The channel has a moving ground with the same velocity and is around 2 meters long. I have simulated the channel with and without a diffuser at the end. The diffuser is 25 cm long and has an angle of 4 degrees. Without the diffuser, my outlet velocity is 21.5 m/s and has an outlet pressure of 0.38 Pa. With the diffuser, the velocity decreases to 12.5 m/s but so does the static pressure, decreases to -1.4 Pa.

Shouldn't the pressure at the outlet increase due to the decrease in velocity, i.e Bernoulli's ?

I have attached velocity contours and the pressure at the outlet

Your kind feedback would be so much appreciated

Mohamed