City Research Online

Abstract

Convective temperature fluctuations (also known as entropy waves or hot/cold spots) generate sound when passing through regions of significant flow acceleration. This is called entropy noise. Entropy noise can be generated by nozzles, as happens in rocket engines, or by turbine blade rows, as in gas turbine engines. While several analytical models have been developed for the former case, not many models exist for the latter due to the more complex physical mechanisms involved. When entropy waves pass through nozzles and blade rows, sound is produced by the acceleration of the entropy waves. In blade rows, three additional mechanisms are in play: (i) the entropy waves are turned, (ii) unsteady forces are induced on the aerofoils by the density fluctuations, and (iii) vorticity is shed from the trailing edges of the blades. All these mechanisms are strongly coupled and affect the total entropy noise generated by the blade rows. In this work, we explore numerically the importance of the last two mechanisms. To this end, we present numerical simulations of entropy waves interacting with three canonical aerofoils: a symmetric NACA 0018 aerofoil at zero incidence, the same aerofoil at an angle of attack, and a flat plate at an angle of attack.

Publication Type:	Conference or Workshop Item (Paper)
Additional Information:	This paper was presented at Inter-Noise 2022, Glasgow, 21-24 August 2022: https://internoise2022.org/
Subjects:	Q Science > QC Physics T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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