The application of radially lobed nozzles has seen renewed challenges in the recent past with their roles in combustion chambers and passive flow control. The free jet flow from such nozzles has been studied for different flow conditions and compared to jets from round nozzles, verifying their improved mixing abilities. The precise mixing mechanisms of these nozzles are, however, not entirely understood and yet to be analyzed for typical jet parameters and excitation modes. While past studies have proposed the presence of spanwise Kelvin-Helmholtz instability modes, the roll-up frequencies of the structures indicate more than one primary structure which is challenging to resolve experimentally.

The present study carries out three dimensional CFD simulations of the flow from a tubular lobed nozzle to identify instability mechanisms and vortex dynamics that lead to enhanced mixing. The model is initially validated against existing hotwire and LDV data following which a range of Large Eddy Simulations (LES) are carried out. The free jet flow was at a Reynolds number of around 3000, based on the effective jet diameter. Initial results are compared to that of a round nozzle to demonstrate changes in mixing mechanisms. The lobed nozzle simulations confirmed the presence of K-H-like modes and their evolution. The interaction of the core jet flow and the ambient was then classified as a function of the Reynolds number and the momentum thickness of the incoming jet flow. We also track the formation and the transport of coherent structures from the tubular part of the nozzle to the core flow, to reveal the evolution of the large-scale streamwise modes at the crests and corresponding horseshoe-like structures at the troughs.

 


Analysis of the Vortex Dynamics and Instability Mechanisms for a Lobed Nozzle Jet

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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