I am investigating annular inlet nozzles for different compressible flow regimes. For simplicity I am using a 2d axisymmetric approach. But for different geometries that I tried, the nozzle chokes at much lower massflows (-30%) than it should be (ideal gas). Does anyone have similar experiences? A Fluent guy mentioned to me once that the massflow predictions of the 2d axisymmetric solver are less reliable. But with 30% discrepancy - do I have to go 3d then? Any help is much appreciated! Thanks!

How are you modelling the case? What are your boundary conditions? Have u taken the same area in 2D?

Mahesh

I am refering to specification data of an aeroengine inlet duct. The case has therefore farfield inlet conditions upstream and a pressure outlet condition at the exit. As it is an axisymmetric case, the inlet duct is circumferential and ends in an annulus. The exit area of the annulus is as in the specification case. With the specified static pressure at the exit, the massflow was about 30% lower than specification. By decreasing the static pressure, I could increase the massflow to 10% less than spec, but the losses obviously become prohibitively high.