[Sabomb]

I have trouble simulating a straight nozzle (exit area 340 mm²). The plenum to the nozzle has an inlet of 260 mm².

According to the simulation result, as shown in the figure, I should be getting a choked flow at the inlet to the plenum. Instead I get about mach 1.07 at the plenum inlet and about mach 1 at the nozzle exit.

I use a mass flow inlet condition with 0.145 kg/s air with ideal gas assumption; Coupled solver, Steady state solution, 2D Axisymmetric and RSM Turbulence model.

The solution I expect to achieve is a sub-sonic flow at the nozzle exit, and hence blame the choking at the plenum inlet for the loss of pressure. Am I not using the right physics? Or is it my understanding of choked flow incorrect?

Thanks in advance!