Noise Reduction in High-Speed Sonic Under expanded jets using Slanted Perforated Tabs

Studies on High-Speed Jet control is of prime importance to aerospace as well as related industries. Proper mixing of Jet of a fuel with the surrounding air is indispensable in the combustion chamber of a propulsive system, this contributes to the need of enhancing mixing of Jet with ambient air. The noise radiated by a jet engine is also a major problem for many cities around the world and this method also reduces the Jet associated noise which is of immense environmental concern for transport aircrafts. The High-speed Jet control is achieved by using two different methods. They are active Control method and passive control method. In active control method, the idea is to introduce stream wise vortices into the mixing layer of the jet. Passive control of the jet can be achieved by adding geometrical modifications. The present study deals with an innovative passive control of jet using slanted perforated tabs. which focuses on the method of changing the structures in turbulent free jets. The experimental study was conducted for different types of Jet coming out from the nozzle. Compressed air is ducted to the settling chamber, where the flow reaches a settled equilibrium. The Pitot probe attached to a traversing mechanism was used for measuring the total pressure in the jet coming out from a convergent nozzle. Single jet flow arrangement was used to carry out the experiments. The centreline Pitot pressure of the uncontrolled jet and the jet with solid tab and different slanted perforated tabs were measured in all three directions. Shadowgraph pictures of the sonic under-expanded jet for these tabs were also captured. A study has been performed for assessing the effectiveness of the slanted perforation tabs. In this study a comparison is made for Jet with rectangular Tab attached at the nozzle exit having different angles of circular perforation. Tab having straight circular perforation and slanted circular perforation of 10-, 20- and 30-degree angles were taken up for this experimental study. These results were also compared with uncontrolled jet and Jet with solid tab. In this study two NPR (NPR3 and NPR4) of Sonic under-expanded jet study was done. In the sonic under-expanded jet study, the results showed that jet with slanted perforated tab was more effective in sonic under-expanded jet than in correctly expanded jet. There was a 27 % reduction in potential core of the sonic under-expanded NPR4 jet for slanted perforated tab as compared to jet with solid Tab and 53.9% reduction in potential core length as compared to uncontrolled jet. The shadowgraph pictures showed that the first shock cell in a jet with slanted perforated tab was greatly disturbed due to the secondary jet coming out of perforation and due to this subsequent shocks became weaker and as a result the jet's potential core reduced. The shadowgraph pictures reconfirmed the findings using the Pitot pressure probe.