Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
What does linear instability analysis tells us about airfoil tonal noise?
Submission Author:
Daniel Rodriguez , Madrid
Co-Authors:
Elmer Gennaro, Walter Arias-Ramirez, William Wolf, Daniel Rodriguez
Presenter: Daniel Rodriguez
doi://10.26678/ABCM.COBEM2017.COB17-0139
Abstract
The understanding and reduction of airfoil self-noise is today a primary concern in the design of low-noise aerodynamic shapes including high-lift components, wind-turbine blades, fans and even car roof racks. Several studies spanning since the 1970s to the present, considering turbulent flow at realistic conditions for aircraft flight, have amassed evidence on the dominance of a far-field tonal noise, usually associated with vortex-shedding from the trailing edge. Furthermore, the appearance of multiple tones has been documented for increasing values of the angle of attack and Mach number, and this tones exhibit a ladder-like structure pattern in terms of the variation of the frequencies with increasing free-stream velocity. Different explanations have been suggested for the origin of the (i) single tone, (ii) multiple tones evenly spaced in frequency and (iii) the ladder-like behavior as free-stream is increased, most of them based on the instability properties of the underlying flow. This contribution presents a comprehensive study of the linear mechanisms possibly acting on a NACA 0012 airfoil, at different Reynolds numbers, angles of attack and Mach numbers. Local and global analyses are performed, on the purpose of extracting all the possible information and eliminating biases associated to the choice of a single methodology. In this sense, ad hoc absolute/convective, multiple-scales analyses, parabolized stability equations and biglobal stability analyses are applied and combined, with the objective of ascertaining if and how airfoil tonal noise can be fully explained, characterized and predicted by linear instability mechanisms. A positive answer to this question would have a tremendous impact regarding flow control and airfoil noise reduction.
Keywords
Flow instability, Aeroacoustics, Computational Fluid Dynamics
