The Aeronautical Journal March 2026 Vol 130 No 1345

In technological applications of jets, such as fuel-air mixing in the combustion chamber, reducing the infrared signature and noise level of the jet, rapid mixing of the jet with the surrounding fluid is required. From vortex theory, it is known that the large-scale vortices are suction creators and the small-scale vortices are mixing-promotors. Therefore, for an efficient mixing of a jet with the surrounding fluid, it is essential to establish an environment consisting of an optimum proportion of the large- and small-scale vortices. But there is no answer to the question of what this proportion is. Hence, the researchers in this field keep attempting to establish the congenial environment of jet mixing with controls.   In this direction, the present work aims to understand the role of jet control in the form of rectangular and triangular shapes with sharp and truncated vertices, placed upright and inverted orientations (triangular, inverted triangular, truncated triangular and inverse truncated triangular tabs).

The mixing promotion caused by a tab is sensitive to the tab geometry and the level of jet expansion. However, these aspects are studied mostly with tabs of specific geometry and specific orientation. Therefore, it will be of value to study the mixing-promoting capability of a tab concerning its orientation, say with the vertex closer to the jet axis and the base closer to the jet axis, in the case of a triangular tab. With this kind of objective, the present study aims at addressing the effect of triangular tabs of sharp and truncated vertex positioned upright and inverse orientations, along diametrically opposite locations at the exit of a Mach 1.6 convergent-divergent circular nozzle, operated at NPRs 3 to 6, in steps of 1, were studied.

The tabs used in this study are triangular tabs with sharp and truncated vertices positioned upright and in inverse orientations, along diametrically opposite locations at the nozzle exit. Mixing characteristics of the jet operated at nozzle pressure ratios (NPRs) 3 to 6, in step 1, were studied. For inverse triangular and inverse truncated triangular tabs, a maximum core length reduction of about 87% is achieved at NPR 3. The corresponding core length reductions caused by the upright triangular and truncated triangular, and rectangular tabs are 71, 81 and 84%, respectively. It is found that the jet mixing is strongly influenced by the combined effect of tab geometry, tip effect, and the pressure gradient at the nozzle exit. The pressure distribution in the directions along and perpendicular to the tab, at different axial locations, was used to discern the evolution and spread of the jet.

The paper Tab orientation effect on jet mixing by E Rathakrishnan appears in Volume 130 Issue 1345 of The Aeronautical Journal and is free to access for one month.

The Aeronautical Journal has, for over a century, been the UK’s leading scientific and technical aeronautics Journal and is the world’s oldest Aerospace Journal that remains in production. Published monthly, The Aeronautical Journal draws upon the expertise and resources of The Royal Aeronautical Society providing a world-wide forum for authors from the UK and overseas. Research papers are solicited on all aspects of research, design and development, construction and operation of aircraft and space vehicles. Papers are also welcomed which review, comprehensively, the results of recent research developments in any of the above topics.

The Royal Aeronautical Society is the world’s only professional body dedicated to the entire aerospace community. Established in 1866 to further the art, science and engineering of aeronautics, the Society has been at the forefront of developments ever since.

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