Boundary layer bypass transition

Numerical studies of bypass transition in the Blasius boundary layer

Experimental findings show that transition from laminar to turbulent flow may occur also if the exponentially growing perturbations, eigensolutions to the linearised disturbance equations, are damped. An alternative non-modal growth mechanism has been recently identified, also based on the linear approximation. This consists of the transient growth of streamwise elongated disturbances, with reg...

Some Characteristics of Bypass Transition in a Heated Boundary Layer

Helical modes in boundary layer transition

Observations are presented to show that in an adverse pressure gradient boundary layer, beneath free-stream turbulence, the interaction between Klebanoff streaks and naturally arising instability waves leads to helical disturbances which break down to form turbulent spots. This occurs under low to moderate levels, 1%–2%, of free-stream turbulence. At high levels of free-stream turbulence, conve...

Delaying transition in rotating boundary-layer flows

We investigate both the type I and II modes of stationary instability within the boundarylayer flow over a rotating disk. Extending the work of previous studies we find that the flow can be stabilised via the introduction of shear-thinning non-Newtonian fluids. Laminar-flow profiles are determined from a generalised von Kármán similarity solution. An asymptotic study is presented in the limit o...

Entropy generation in bypass transitional boundary layer flows

The primary objective of this study is to evaluate the accuracy of using computational fluid dynamics (CFD) turbulence models to predict entropy generation rates in bypass transitional boundary layers flows under zero and adverse pressure gradients. Entropy generation rates in such flows are evaluated employing the commercial CFD software, ANSYS FLUENT. Various turbulence and transitional model...