Eventos Anais de eventos
EPTT 2022
13th Spring School on Transition and Turbulence
Analysis of the boundary layer intermittence and turbulent transition due to a gap.
Submission Author:
Felipe Oliveira Aguirre , SP
Co-Authors:
Felipe Oliveira Aguirre, Marlon Sproesser Mathias, Marcello Augusto Faraco de Medeiros
Presenter: Felipe Oliveira Aguirre
doi://10.26678/ABCM.EPTT2022.EPT22-0041
Abstract
The interaction of the boundary layer with small surface irregularities has been studied in several contexts. Several studies reveal that some configurations of gaps, also called small cavities, can induce boundary-layer disturbances due to the presence of unstable hydrodynamic modes. The literature presents results where, in some scenarios, the presence of gaps can induce boundary layer transition through the bypass transition phenomenon. To better understand this scenario, a representative case was chosen, where the transition occurs after a transition zone along the length of the flat plate. For this case, it was analyzed how the unstable modes predicted in linear stability theory behave in the flow. Initially, it was investigated how these modes behave inside the cavity, interacting and subsequently being convected out of the cavity. Subsequently, the convected structures were followed along the domain, to understand if there is memory of the flow structures present inside the cavity. We observed the presence of unsteady two-dimensional modes in the mixing layer, known as Rossiter modes, and unstable three-dimensional modes inside the cavity, known as centrifugal modes, which are subsequently convected into the boundary layer downstream of the cavity. Analyzing the intermittent region, where the flow oscillates between turbulent and laminar, it was possible to notice that the Rossiter and Centrifugal modes are present in this region, interacting with each other. Finally, through the analysis of the turbulent region, it is possible to note the presence of memory of the centrifugal modes present in the cavity, as well as the presence of residual modes with a frequency close to the Rossiter modes.
Keywords
Boundary Layer, Flow instability, transition to turbulence, DNS, open cavity
