Numerical Study of the Effect of Freestream Turbulence on by-pass Transition in a Boundary Layer
Article dans une revue avec comité de lecture
Date
2014Journal
Energy ProcediaAbstract
We use direct numerical simulations in the presence of free-stream turbulence having different values of intensity, T u, and integral length scale, L, in order to determine which kind of structures are involved in the path to transition of a boundary-layer flow. The main aim is to determine under which conditions the path to transition involves structures similar to the linear or non-linear optimal perturbations. For high values of T u and L, we observe a large-amplitude path to transition characterized by localized vortical structures and patches of high- and low-momentum fluctuations. Such a scenario is found to correlate well with the L and hairpin structures resulting from the time evolution of non-linear optimal perturbations, whereas, for lower T u and L, a larger correlation is found with respect to linear optimal disturbances. This indicates that a large-amplitude path to transition exists, different from the one characterized by elongated streaks undergoing secondary instability. To distinguish between the two transition scenarios, a simple parameter linked to the streamwise localisation of high- and low-momentum zones is introduced. Finally, an accurate law to predict the transition location is provided, taking into account both T u and L, valid for both the transition scenarios.
Files in this item
Collections
Related items
Showing items related by title, author, creator and subject.
-
Article dans une revue avec comité de lectureFARANO, Mirko; CHERUBINI, Stefania; DE PALMA, Pietro; ROBINET, Jean-Christophe (Springer Verlag, 2017)Bursts are recurrent, transient, highly energetic events characterized by localized variations of velocity and vorticity in turbulent wall-bounded flows. In this work, a nonlinear energy optimization strategy is employed ...
-
Article dans une revue avec comité de lecturePARENTE, ENZA; DE PALMA, Pietro; CHERUBINI, Stefania; ROBINET, Jean-Christophe (Cambridge University Press, 2022)Recently, many authors have investigated the origin and growth of turbulent bands in shear flows, highlighting the role of streaks and their inflectional instability in the process of band generation and sustainment. ...
-
Article dans une revue avec comité de lectureCHERUBINI, Stefania; DE PALMA, Pietro; BOTTARO, Alessandro; ROBINET, Jean-Christophe (IOP Publishing, 2012)The understanding of transition in shear flows has recently progressed along new paradigms based on the central role of coherent flow structures and their nonlinear interactions. We follow such paradigms to identify, by ...
-
Article dans une revue avec comité de lectureCHERUBINI, Stefania; DE PALMA, Pietro; BOTTARO, Alessandro; ROBINET, Jean-Christophe (American Physical Society (APS), 2010)Recent studies have suggested that in some cases transition can be triggered by some purely nonlinear mechanisms. Here we aim at verifying such an hypothesis, looking for a localized perturbation able to lead a boundary-layer ...
-
Article dans une revue avec comité de lectureCHERUBINI, Stefania; DE PALMA, Pietro; BOTTARO, Alessandro; ROBINET, Jean-Christophe (Cambridge University Press (CUP), 2011)This paper describes a scenario of transition from laminar to turbulent flow in a spatially developing boundary layer over a flat plate. The base flow is the Blasius non-parallel flow solution; it is perturbed by optimal ...