Validated Computational Tonal Noise Prediction for Airfoils with a Laminar Separation Bubble

Abstract

A computational aeroacoustic study of a laminar separation bubble (LSB) in close proximity to the airfoil trailing edge (TE) examines the aerodynamic source of the generated tonal noise and the influence of acoustic feedback on tonal noise amplification. Incompressible wall-resolved large-eddy simulation (LES) and the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy are applied to the SD 7037 airfoil at the Reynolds number, 𝑅𝑒, of 41000. At 1 deg angle of attack (AOA), the FW-H acoustic analogy accurately predicts the tonal noise frequency, which originates from the Kelvin–Helmholtz (K-H) rolls in the LSB shedding past the airfoil TE, and a secondary tone occurs due to intermittent spanwise breakdown of the K-H rolls. An estimation of the interference between the TE acoustic feedback and the recently identified LSB pressure feedback shows that destructive interference at 3 deg AOA lowers the tonal noise, while constructive interference at 1 and 5 deg AOA amplifies the tonal noise. This study of the tonal noise generated by an LSB shows that destructive interference of the LSB and TE feedback mechanisms can be exploited as a mechanism of active tonal noise control for airfoils operating at low 𝑅𝑒.