Research Projects

Controlling acoustic emissions from a supersonic jet remains one of the most enduring challenges in aerospace engineering. Particularly, an intense tonal noise, referred to as ‘screech’, is generated by a nonlinear acoustic feedback loop involving instability waves, shock-cell structures, and upstream-propagating acoustic waves. While a considerable body of literature exists on screech dynamics in axisymmetric nozzles, especially circular ones, modern aerospace systems with propulsion configurations involving significantly complex nozzle geometries have yet to be characterized for their acoustic signatures. Serpentine nozzles, characterized by internal curvature and non-axisymmetric exits, have gained prominence in stealth-class aircraft for their ability to reduce radar and infrared signatures. However, the flow asymmetries, shear layer distortion, and shock-structure deformation induced by such geometries are expected to substantially influence the screech mechanisms. Despite the increased use of serpentine nozzles, a detailed understanding of the aeroacoustics of these configurations remains elusive. The proposed study hypothesizes that the internal curvature and the exit aspect ratio fundamentally alter screech staging and feedback closure mechanisms by modifying the growth of the shear layer, increasing shock-cell decay, and thereby influencing the emergence of guided jet modes (GJM). Specifically, it is anticipated that the breakdown of axial symmetry and the introduction of curvature in a serpentine nozzle leads to changes in the dominant screech mode, suppression of modal staging, and spatial redistribution of the acoustic source region. A key scientific objective of the proposed study is to map the conditions under which the curvature suppresses or alters the screech behavior, thereby characterizing the stealth nozzle design from both a fluid dynamic and acoustic standpoint. To test this hypothesis, an extensive experimental campaign will be carried out using geometrically varied serpentine nozzles with controlled centreline offsets and aspect ratios. Experiments conducted for a range of nozzle pressure ratios (NPR) ranging from 2 to 5 will explore both underexpanded and moderately expanded jet conditions. While the far-field microphone arrays will be used to localize acoustic sources, time-resolved Schlieren imaging in the near-field will visualize shock structures and identify the screech source region. Further, Particle Image Velocimetry (PIV) will be employed to quantify the velocity field and shear-layer development, helping to relate flow physics to acoustic emissions. Preliminary acoustic data will be acquired at IIEST Shibpur, and high-speed diagnostics (PIV and Schlieren) will be conducted at CSIR-NAL, Bengaluru. The novelty of this research lies in its holistic treatment of nozzle geometry and jet acoustics, bridging fundamental studies and practical aerospace applications. The research efforts will generate novel datasets and provide a mechanistic understanding of screech in non-axisymmetric, stealth-relevant nozzles, a topic that is currently underexplored. Outcomes of the study are expected to feed directly into the design of low-signature propulsion systems, where the performance, acoustic compliance and detectability must be jointly optimized. Furthermore, the screech maps and flow-acoustic correlations developed here will serve as validation tools for future simulations and design frameworks in advanced jet noise mitigation.