Mixing performances of five different supersonic nozzles namely: elliptical, tabbed, conical, radially lobed and two-dimensional lobed were compared experimentally. The experiments aimed to provide comparisons of mixing performance under identical conditions with that of convential mixing nozzles. The mixing of the supersonic stream with a coaxial sonic stream coming from the nozzle was investigated non-intrusively using digital image processing of planer Mie-scattering images of the flow fields.

R. I. Sujith

Department of Aerospace Engineering

Thiruchengode M. Muruganandam

combustion

Image processing

Jets

Nozzles

Scattering

COAXIAL JETS

Mixing

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Experiments in Fluids

Studies on mixing enhancement with two dimensional (2D) lobed nozzle have been conducted in a dual stream supersonic flow facility. The distributions of momentum flux, stagnation pressure and stagnation temperature across a plane at different axial distances from the nozzle exit were considered as a measure of mixing. The results indicated an enormous enhancement in mixing when 2D lobed nozzle was employed in comparison with conventional plain 2D nozzle. The enhanced mixing performance could be attributed to the large scale axial vortices observed in the flow-field of subsonic lobed nozzles by earlier investigators.

Experimental study on mixing enhancement in two dimensional supersonic flow

A radially lobed nozzle (petal nozzle) is being increasingly recognised as a potential candidate for promoting mixing in compressible flows. An experimental investigation has been conducted to study its effectiveness in improving thermal mixing and combustion in supersonic flow. A hot gas jet issuing supersonically from a lobed nozzle mixes with a cold supersonic jet in a circular mixing tube. The two jets issue coaxially. A detailed survey of the flow field inside the mixing duct reveals that nearly complete thermal mixing (as exemplified by the nearly uniform temperature distribution) could be achieved in a short distance when a lobed nozzle is employed. The results also indicate the presence of large-scale vortices in the flow field downstream of the lobed nozzle. Having thus created a field in which mixing is good, supersonic combustion was then attempted. Kerosene was introduced into the hot stream issuing from the lobed nozzle and it burned mainly in the mixing tribe, which served as a supersonic combustor. Resulting temperature and pressure rises were measured and the supersonic combustion efficiency was found to be of the order of 60%. The performance of a conventional conical nozzle was found to be much inferior to that of the petal nozzle under identical conditions.

Combustion and Flame

An experimental investigation of thermal mixing and combustion in supersonic flows

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