[mjkey]

Hi guys,

I'm currently doing an analysis at work for the pressure drop across a converging nozzle. Nozzle is used for supply air ventilation into a train tunnel. Due to probity and confidentiality I am unable to post any pictures, but here is a brief description of the geometry and flow conditions

The nozzle has the inlet, with air flowing horizontally (i.e left to right) and then has a 30degree transition downwards and makes it way to the outlet. The overall length of the nozzle is about 4m.

Nozzle Inlet Area: 8m2
Nozzle Outlet Area: 2m2
Nozzle Inlet Volume Flow: 65m3/s
Trying to understand: The pressure drop across the nozzle.

The boundary conditions i applied in CFX:
Inlet: Volume Flow Rate
Outlet: Averaged Static Pressure
Walls: No slip wall

Result:
I was getting a whopping 700Pa loss across the nozzle. Comparing this to previous project example, they were getting maximum 60Pa loss across their nozzles of a similar shaped geometry and similar flow rates. Either they were fudging their numbers (i only have a report to read off for their results) or I am doing something wrong.

Question: Am I applying the correct boundary conditions for this sort of case in CFX? Is a 700Pa loss across this nozzle really possible?

Thanks guys! (First post here )