Title: Investigating the effect of nozzle length variation on centreline decay using AI predictions

Authors: J. Anbarasi; Naren Shankar Radha Krishnan; Rohan Bastola; Rajamurugu Natarajan

Addresses: Department of Aeronautical Engineering, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, India ' Department of Aeronautical Engineering, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, India ' Department of Aeronautical Engineering, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, India ' Department of Aerospace Engineering, KCG College of Technology, Chennai, India

Abstract: This study investigates how nozzle length affects centreline pressure decay and potential core length of subsonic jets, using AI to enhance prediction accuracy. Understanding nozzle geometry's effect on jet behaviour is critical for propulsion, noise control, and industrial jet design. Experiments and simulations covered nozzle lengths from 0 mm (orifice) to 100 mm and diameter ratios of 2, 3, and 4 under subsonic, sonic, and under-expanded conditions. A rational quadratic gaussian process regression (RQGPR) model predicted centreline total pressure based on velocity ratios between primary and minor jets. Results show core length increases significantly up to 30 mm nozzle length, then plateaus. For diameter ratio 3 at subsonic flow conditions, a 16% and 31% increase in the core length was observed for nozzle lengths of 10 mm and 30 mm. Decay is delayed by expansion waves of under-expanded jets and the core is elongated, leading to a supersonic flow transition.

Keywords: jets; turbulent models; potential core length; nozzle pressure ratio; shadowgraph; shock.

DOI: 10.1504/IJSA.2025.148749

International Journal of Sustainable Aviation, 2025 Vol.11 No.3, pp.302 - 320

Received: 27 Mar 2025
Accepted: 22 May 2025
Published online: 22 Sep 2025 *

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