On the Evolution of Vortical Disturbances in Two-Fluid Boundary Layers
Abstract
The low-frequency free-stream disturbances penetrate boundary layer despite the sheltering ability of the mean shear. These disturbances form streaks via the lift-up mechanism. The streaks subsequently become unstable and breakdown to turbulence. The stability of laminar boundary layers is examined in presence of a thin wall-film, of different viscosity. The influence of the film on the evolution of free-stream vortical modes and the generation of boundary layer streaks is solved analytically. It is shown that a lower viscosity film can reduce the transient amplification due to the lift-up mechanism, and hence enhance the flow stability. However, the presence of the wall-film also introduces a new mechanism for the generation of normal vorticity. This mechanism become dominant when the viscosity of the lower film is reduced below a critical level. The results from the linear analysis are complemented by direct numerical simulations which take into account non-parallel and non-linear effects, e.g. finite displacement of the two-fluid interface.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 2011
- Accession Number
- ADA547949
Entities
People
- Tamer A. Zaki
Organizations
- Imperial College London