Abstract In this study four different supersonic nozzles -circular, elliptical, tabbed, and radially lobed nozzles are compared experimentally for their freejet mixing performance. With the background of studies by various groups conducted on elliptical, tabbed, and radially lobed nozzles, the present paper aims at a comparative experimental study to compare their mixing performance with that of a conventional circular nozzle under identical operating conditions. The investigation is performed non-intrusively, using digital image processing of the planar Mie scattering images of the flow field. The results of these investigations reveal the superiority of the mixing performance of the lobed nozzles over conventional circular and other non-conventional nozzles.

Thiruchengode M. Muruganandam

Department of Aerospace Engineering

R. I. Sujith

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Experiments in Fluids

The freejet characteristics of radially lobed nozzles were studied experimentally. Schlieren photographs of the freejets revealed that the lobes of the nozzles gave rise to alternate expansion-compression regions. For two of the lobed nozzles the potential core was reduced by a factor of three relative to the conical nozzle tested. The jet spread and the shear layer thickness of the lobed nozzles were considerably higher than those for the conical nozzle. The jet width and the shear layer thickness were higher in the major plane; however, the shear layer growth rate was higher in the minor plane of the lobed nozzles. Jet axial thrust measurements revealed a thrust loss of 14% for two of the lobed nozzles tested. © 1995 Springer-Verlag.

Studies on freejets from radially lobed nozzles

Currently, the focus of attention in aerospace propulsion research has been on the development of advanced air-breathing propulsion systems like scramjets, air-augmented rockets, multimode engines for the hyperplane, etc. A crucial technical problem to be tackled in such systems is the enhancement of mixing between two highspeed gaseous streams. Various methods have been tried so far, but the field is still very much an open one. Tests conducted earlier on subsonic flow mixing have shown that large-scale secondary flows, and not viscous diffusion, are the key to quick, low-loss, efficient mixing. In this regard, a lobe-type, convergent-divergent, supersonic nozzle, named the "Petal" nozzle, was designed, fabricated, and tested. Near-complete mixing with low total momentum loss within a short mixing chamber of length to diameter ratio of 4.35 was achieved. © 1993 American Institute of Aeronautics and Astronautics, Inc.

Journal	Experiments in Fluids
ISSN	07234864
Open Access	No