Tese e Dissertação

Tese: On the formation of a laminar separation bubble in a two dimensional boundary layer

The formation and breakdown of laminar separation bubbles (LSB) typically play a significant role in aerodynamic performance and acoustic noise emission of airfoils operating at low Reynolds numbers. The LSB is subjected to a time-varying level of environmental disturbances in many practical applications, such as turbine cascades and UAV rotors. This work investigates the formation of a laminar separation bubble in a water channel at strictly controlled disturbance conditions. An electromagnet and a thin metal stripe upstream of the separation are used as a disturbance source. The device can promote boundary layer laminar-turbulent transition in a controlled fashion and momentarily suppresses the LSB. Thus, the bubble formation can be initiated by a sudden reduction in the level of generated disturbances. The setup allows the study of the transient process from the incipient separation of the boundary layer until the quasi-stationary regime. The time-resolved Particle Image Velocimetry (PIV) technique is employed to measure this transient process. Phase-locked ensemble average schemes were used. The results describe in great detail the asymptotic evolution of the bubble topology and the velocity flow field. The dominant flow structures were assessed by applying modal analysis techniques such as reduced order variational mode decomposition (RVMD) and fast and adaptative empirical mode decomposition (FAEMD). The proper orthogonal decomposition (POD) technique was also employed for quasi-steady regimes. The most energetic modes succeed in reproducing the asymptotic growth of the LSB, suggesting that reduced models can be used in simulations and active control strategies.

Link da defesa:

https://puc-rio.zoom.us/j/96898289774?pwd=MgMTNhV5fGnDQ3QIPUukbxuM9ZdTP1.1#success

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