Analysis of in-flight behavior of truncated plug nozzles

Plug nozzles are usually designed to achieve altitude adaptation in a wide range of chamber/ambient pressure ratios. In actual in-Right operations of plug nozzles, this phenomenon must take place in a Rowing airstream, which can affect the performance, To understand the how behavior in such conditio ns and to evaluate the departure from the ideal nozzle performance, an inve stigation is carried out with a validated numerical tool based on the solut ion of turbulent Navier-Stokes equations and on shock fitting. A sample roc ket plug nozzle is analyzed parametrically to evaluate the effect of varyin g Mach number at constant pressure and the effect of varying pressure ratio at constant Mach number. The results indicate that the interaction with a flowing airstream reduces the pressure of the external air, as seen from th e nozzle exhaust jet, yielding a reduction of the performance. In particula r, a dramatic decrease of nozzle performance may take place in the transoni c region if the slipstream effect is neglected in the design, The results a lso provide useful indications on how the Mach number and the shroud shape can affect the value of ambient pressure where the transition from open to closed wake takes place.