Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
On the absolute instability of laminar separation bubbles
Submission Author:
Mateus Avanci , RJ
Co-Authors:
Daniel Rodriguez, Leonardo Santos de Brito Alves, Mateus Avanci
Presenter: Mateus Avanci
doi://10.26678/ABCM.COBEM2017.COB17-0666
Abstract
Laminar separation bubbles occur due to separation, transition, and turbulent reattachment of the boundary- layer flow under adverse pressure gradients. They can appear in many practical flows, as aircraft airfoils or turbine blades. The stability characteristics of separation bubbles are studied here using the Orr-Sommerfeld equation and its inviscid analogous, the Rayleigh’s equation. Base flow velocity profiles are modelled by a modified hyperbolic tan- gent function, and characterized with respect to their maximum reverse flow and the distance from the inflection point to the wall. Linear stability theory (LST) was used to identify the transition from convective to absolute character of Kelvin-Helmholtz instability. Two complementary approaches are used, namely a matrix- forming one based on spatial discretization of the equations using a spectral method that allows for the computation of the complete eigenspectra, and a shooting method for Rayleigh’s equation that makes the parametric study very efficient.
Keywords
Laminar separation bubble, Boundary layer separation, Absolute/convective instability
