Unfortnatley there just is not the pressure to choke the flow at the throat in a model turbine.

To obtain sonic velocity at the throat you must drive you flow with a pressure greater than the critical pressure ratio, which is 1.89 . Therefore if ambient is 101325 then the total pressure just aft of the turbine must be 191504 Pa. Model turbines are just nowhere near that , or certainly the one I measured, (it was much nearer an NPR of 1.3)

So really the statement , "it would be alot of work", is on the right track ! , I think it would be more like a completely redesigned engine to obtain a choked nozzle !

We are starting to see model axial compressors in engines now, I wonder what NPR's these are operating at.


Nick