Experimental Investigation of Four-finned Tab Controlled Subsonic and Sonic Jets

Mixing enhancement of jets at the exit of nozzle plays a significant role in improving the stealth capability of military aircraft, reducing jet noise, and enhancing combustion efficiency. Passive control devices are widely preferred for jet control due to their simple design and the absence of external energy requirements. Among them, tabs have been identified as effective devices for promoting jet mixing characteristics for subsonic and sonic operating conditions. The present study experimentally investigates the effect of stem-alone and four-finned tab configurations on jet mixing at subsonic and sonic Mach numbers. Two diametrically opposite tabs were mounted at the circular nozzle outlet. Axial and radial pressure measurements were carried out to analyze jet decay, spreading, and mixing characteristics, while shadowgraph visualization was employed to capture the near-field shock structures developing downstream of the nozzle for Nozzle pressure ratio (NPR) 4. The influence of Mach number on jet mixing performance was also examined. Results showed a noticeable reduction in potential core length for both controlled configurations compared to the baseline jet. The maximum reduction of 90% in potential core length was achieved by the four-finned tabs. The jet decay slope was higher for tab-controlled cases, with the maximum observed for the four-finned tab under sonic conditions. Radial pressure distributions indicated greater jet spreading and larger off-center peak distances in the near and intermediate field regions for the four-finned tab. Higher Mach numbers further improved jet decay and spreading. Shadowgraph results also revealed weakened downstream shock structures, indicating improved mixing and reduced noise potential.