Vortical Mode Interactions and Bypass Transition Delay in Two-Fluid Boundary Layers
Lead Research Organisation:
Imperial College London
Department Name: Mechanical Engineering
Abstract
Two-fluid shear flows are ubiquitous in engineering and environmental fluid mechanics. Examples include the boundary layer above deicing agents in aerodynamics, surface cooling using a liquid film sheared by an external gas flow, and the interaction the atmospheric boundary layer with ocean waves. The instability of these two-fluid flows is clearly significant: the aerodynamic lift and drag depend on the state of the boundary layer around the airfoil, the cooling rate of sheared films depends on the disturbance level in the flow, and the instability of ocean waves leads to breakdown and sea sprays.In this proposal, the canonical problem of a boundary layer above a film of different viscosity and density is studied. The flow is subjected to free-stream turbulence, similar to what is observed in engineering and environmental flows. This interaction causes a laminar boundary layer to breakdown to a chaotic, or turbulent, state in a manner known as bypass transition. In the proposed research, the stability of the boundary layer is compared in the presence and absence of an underlying film. It is expected that, depending on the properties of the film, the breakdown to turbulence can be accelerated or delayed. Since turbulence enhances mixing and, as a result, viscous drag, our interest is in transition delay which can lead to significant cost savings via drag reduction. The research will include two components: perturbation analysis and numerical simulations. The analysis will focus on fundamental aspects of the interaction between flow disturbances and the two-fluid boundary layer, for example how a vortical perturbation is affected by the presence of the interface between the two fluids. The simulations will provide a numerical laboratory where the full non-linear breakdown process from laminar to turbulence is simulated, and the role of the underlying film quantified. The combination of the analytical and numerical approaches will provide a comprehensive view of the interaction of free-stream perturbations with the two-fluid boundary layer. Despite the focus on the canonical boundary layer problem, the proposed framework is general and is applicable to a host of other engineering and environmental two-fluid shear flows.
Organisations
People |
ORCID iD |
Tamer Zaki (Principal Investigator) |
Publications
Zaki T
(2013)
From Streaks to Spots and on to Turbulence: Exploring the Dynamics of Boundary Layer Transition
in Flow, Turbulence and Combustion
VAUGHAN N
(2011)
Stability of zero-pressure-gradient boundary layer distorted by unsteady Klebanoff streaks
in Journal of Fluid Mechanics
Saha S
(2016)
Disturbance amplification in boundary layers over thin wall films
in Physics of Fluids
Lee J
(2013)
Effect of wall heating on turbulent boundary layers with temperature-dependent viscosity
in Journal of Fluid Mechanics
Lee J
(2014)
Turbulent thermal boundary layers with temperature-dependent viscosity
in International Journal of Heat and Fluid Flow
Jung S
(2015)
The effect of a low-viscosity near-wall film on bypass transition in boundary layers
in Journal of Fluid Mechanics
Jones B
(2011)
Flow Estimation of Boundary Layers Using Wall Shear Information
in IFAC Proceedings Volumes
Durbin P
(2009)
Interaction of discrete and continuous boundary layer modes to cause transition
in International Journal of Heat and Fluid Flow
Cheung L
(2010)
Linear and nonlinear instability waves in spatially developing two-phase mixing layers
in Physics of Fluids
Cheung L
(2011)
A nonlinear PSE method for two-fluid shear flows with complex interfacial topology
in Journal of Computational Physics
Description | We demonstrated that we can substantially control the onset of chaos in fluid motion by using a very thin fluid film. We can thus control drag. This effect has significant impact on energy and environmental sustainability in a host of applications where drag is a key factor. |
Exploitation Route | The work has been extensively cited. It has also been recognized by our peers and industrial partners, and is being exploited for more complex configurations. |
Sectors | Aerospace Defence and Marine Energy Transport |
Description | This work has led to novel ways to exploit two-fluid interfaces in drag reduction and transition delay -- both key contributions to our efforts towards energy and environmental sustainability. |
First Year Of Impact | 2012 |
Sector | Aerospace, Defence and Marine,Transport |
Impact Types | Societal Economic |