An Experimental and Numerical Investigation of Swirling Flows in a Rectangular Nozzle

Abstract

The high thrust to weight ratios now possible for military aircraft have made thrust vector pitch control more attractive and versatile than aerodynamic surface pitch control. Use of a rectangular nozzle is a natural consequence because articulation and sealing problems are less formidable than for conventional circular ones. The rectangular nozzle offers the additional possibility that the exhaust may mix rapidly with the ambient air and thereby reduce the radiative signature of the exhaust. A detailed experimental investigation is described, which demonstrates that the formation of axial vortices in the nozzle is dependent on the vorticity distribution at the turbine exhaust. Further, three mechanisms which provide for the formation of axial vortices are identified. A parallel computational investigation was carried out which not only confirmed the relationship between the turbine exhaust vorticity and the vortex pattern formed in the nozzle but also provided details of the flow field between the turbine discharge and the nozzle exit. On the basis of this more detailed understanding, it is now possible to tailor the vortex distribution at the nozzle exit by design of the turbine discharge and the intervening passage.