Direct numerical simulations of noise generated by turbulent flow over airfoils

Abstract

A direct numerical simulation (DNS) is conducted of the turbulent ∞ow around a NACA0012 airfoil at incidence. The upper airfoil surface exhibits laminar separation, transition and reattachment as a turbulent boundary layer, whereas the lower surface remains laminar and attached for the entire airfoil chord. The aim of the study is to investigate the mechanisms of noise generation and to potentially identify sources of airfoil noise other than trailing edge noise. In particular we are interested in the conditions under which the airfoil self-noise can be predicted accurately using the classical trailing edge theory of Amiet, where the farfleld sound is evaluated from the convecting surface pressure spectrum upstream of the trailing edge. The DNS data are used to examine assumptions made in the theory. It is shown that for certain frequencies the sound radiation difiers signiflcantly from that expected from trailing edge theory, and that at least one additional noise source is present, distinct from the airfoil trailing edge.