Gunshot localization

Modern gun-battles are rarely waged on open ground where enemies face each other, and the origin of unfriendly and friendly fire are easy to locate. Instead, most combats are now staged in obstacle-dense situations like cities, forests and mountain valleys, where the location of a shooter may be difficult to pinpoint aurally due to reverberations. More importantly, our security forces may not even be present within audible range of all gunshots at all times, due to the highly mobile nature of modern combat. However, in these situations, the personnel would still desire real-time knowledge of the origin of unfriendly fire so as to prepare prompt and effective counter-measures. We are developing a system that can robustly detect and localize gunshots based on acoustics in scenarios of relevance to internal security. A minimal number of low-cost microphones and associated electronic circuitry distributed over the zone of conflict will feed into an efficient real-time algorithm with minimal human interaction.

The acoustic signature of a gunshot consists of two parts. The explosion of the propellant that discharges the bullet is called the 'muzzle blast', and the resultant acoustic waves travel spherically outward from the end of the muzzle. If the bullet travels with supersonic speed, then an additional shock wave is generated that trails as a cone behind the bullet. The two signatures can be distinguished in the microphone signal, and they can be used in concert to pinpoint the location of the shooter. In particular, the algorithms that apply to the muzzle blast are closely related to those used in Global Positioning Systems (GPS). The figure presents the microphone signal recorded in experiment where an AK-47 rifle was fired. The shock wave from the supersonic bullet arrives at the microphone before the muzzle blast reaches it. The ground reflection from these events are also captured.

Robust algorithms that pinpoint the muzzle blast are being developed. Parallely, we are developing a standalone microprocessor-based hardware implementation of the localization system. The final system is intended to be sufficiently automated and intuitive so that the users can concentrate more on the mission at hand.

Modeling coherent wavepackets in jets issuing from serrated nozzles

We have developed models based on linear parabolized stability equation (PSE) theory for the coherent wavepackets in jets issuing from serrated nozzles (also called chevron jets). Subsequently, we have used this modelling technique to understand the effect of varying the chevron geometry on the stability characteristics of such jets, in an effort to predict the corresponding noise behaviour. The overall aim is to optimally design the chevron geometry for noise mitigation, with minimal computational effort.

Selected publications:

  • A. Sinha, A. Rajagopalan and S. Singla, Linear stability implications of chevron geometry modifications for turbulent jets, AIAA Paper 2016-3053 (download)
  • A. Sinha, K. Gudmundsson, H. Xia and T. Colonius, Parabolized stability analysis of jets from serrated nozzles, Journal of Fluid Mechanics, 789:36-63, 2016 (download)
  • A. Sinha and T. Colonius, Linear stability implications of mean flow variations in turbulent jets issuing from serrated nozzles, AIAA Paper 2015-3125 (download)

Modeling coherent wavepackets in dual-stream jets

The parabolized stability equation (PSE) theory is applied to dual-stream coaxial jets in an effort to predict the coherent wavepackets existing therein. In collaboration with Prof. Datta V. Gaitonde of Ohio State University (Columbus, Ohio, USA), we have compared the model results against Large-Eddy Simulation (LES) data of two such coaxial jets, with reasonable success. The ultimate goal is to add to the toolkit for prediction of noise reduction potential of offset multi-stream jets that are being experimentally evaluated at present.

Selected publications:

  • A. Sinha, D. V. Gaitonde and N. Sohoni, Parabolized stability analysis of dual-stream jets, AIAA Paper 2016-3057 (download)