[huangxianbei]

Hi, all
My case is a hydraulic intake with a vertical pipe. The domain is decomposed into 3: intakeair(the air region above the water surface), intakewater(the water region in the tank) and the pipe region, the interface between the regions are AMI. Attached is the setup of the case except the mesh. In the experiment, the water level is kept as constant. Under this submergence, certain amount of air will enter the water domain. The volumetric flow rate at inlet of the intakewater is used and the static pressure at atmosphere(airtop) is used with prghpressure. According to what I have already know, the pressure condition for the patches including walls should be fixedFluxPressure. The inlet flow is 0.015m3/s and hence the velocity at the outlet in the pipe domain is 2.472m/s. The inlet of the intakeair is set to be 0m/s. The calculation is steady, while the unexpected phenomenon is that the water level is decreasing along with time as shown in following.
0s-initial condition
https://www.cfd-online.com/Forums/members/huangxianbei-albums-patel-picture896-0s.png

2s
https://www.cfd-online.com/Forums/members/huangxianbei-albums-patel-picture897-2s.png

This is quite strange as I have already performed a simulation by CFX and the water level was constant as in the experiment. Does anyone know how to solve this problem? Any comment would be really appreciating.