Conference_programme: 2.1 - Aeroacoustics
Lecture: On the effects of vorticity on the acoustic field through a scalar operator based on total enthalpy terms
Author(s): Legendre Cesar , Debrye Benjamin , Detandt Yves , Lielens Gregory , Van Den Nieuwenhof Benoit
Summary:
Sound propagation through arbitrary complex media is often studied using the linearized equations of motion and energy, for instance, the linearized Navier-Stokes equations (LNSE) or in the absence of viscous effects, the linearized Euler equations (LEE). Although such equations are exact assuming linear acoustics, instabilities may occur under strong flow conditions, i.e. Kelvin-Helmholtz (K-H) instabilities, making these sets of equations numerically unstable. In this work, a scalar acoustic operator based on total enthalpy terms and including mean flow rotational effects is presented. Two hypotheses are considered concerning the wave propagation; the absence of entropy (homentropic acoustics) and vortical waves. In addition, the acoustic operator evidences that the ratio between the mean vorticity and the angular frequency plays a crucial role in: (i) the range of validity of the operator; (ii) the possible limit of linear acoustics under shear flow conditions; (iii) a proposal for the definition of high (low) mean vortical flows in the wave propagation context; and (iv) the occurrence of shear-acoustic instabilities (i.e. K-H) in linear acoustics. Finally, the operator is numerically validated against LEE's solutions (reference theory) on several cases including sound propagation through: (a) two counter-rotating vortices (Lamb-Chaplygin vortex); (ii) a duct flow with boundary layers; (iii) a cylindrical jet flow; and (iv) a realistic aircraft engine exhaust.
Corresponding author
Name: Dr César Legendre
e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Country: Belgium
