Wind tunnel tests and fluid dynamics analyses of wake flows near blunt and streamlined bodies models at high reynolds numbers

Abstract

This PhD thesis presents three different research accomplishments, as summarized below. Firstly, a new methodology is proposed to measure and analyze the flow characteristics near blunt bodies without introducing physical probes into the flow-field, which would alter the flow behavior. This methodology analyses the wake region of a “Ground Surveillance System” (Radar), with the aim to evaluate the turbulence intensity, drag coefficients, pressure distribution coefficients, and boundary layer separation. The numerical results obtained on the radar’s wake region showed periodic vortex shedding, boundary layer separation, high levels of turbulence, and induced drag; the nature of the adverse pressure gradient and the high turbulence intensity values at the radar surface needed a mechanism to reduce flow fluctuations and to allow the boundary layer increase. Foils subjected to a fluid flowing axially from the free end towards the clamped-end, known as “inverted-foil” configurations, have been observed experimentally for large-amplitude flapping beyond a critical flow velocity. The motivation for further research on the dynamics of inverted-foils is due to its presence in nature and engineering. It was found from experimental results that, for foils with aspect ratio AR<1, the undeflected static equilibrium was stable prior to a sudden bifurcation. For foils with AR≥1, however, the undeflected stable static equilibrium was subjected to a slow bifurcation, associated with its buckling. Higher flow velocities generated a flapping motion around the deflected static equilibrium. At higher flow velocities, flapping motions are symmetric around the undeflected static equilibrium. Experiments with foils in a reverse axial flow were conducted in our Price- Païdoussis subsonic wind tunnel at ÉTS. Numerical results were validated with experimental results for parameters, such as the foils lengths (aspect ratios), flapping frequency and regime, Strouhal and Reynolds numbers, flapping amplitudes and forces for energy harvesting purposes. The role of Unmanned Aerial System (UAS) operations has increased in recent years. A new multidisciplinary methodology is presented for the design, aerodynamic optimization, and model validation of an adaptive wing prototype. The research performed on the UAS-S45 focused on replacing the conventional rigid wing with an adaptive wing system capable of actively changing the wing's shape. The experimental and simulated results have shown a low drag production and a high lift-to-drag ratio of the adaptive wing prototype that translates into a reduction in fuel consumption and an increase in cruising flight range and therefore into climate improvement.

Date	30 Jul 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Ruxandra Botez (Supervisor) & Guy Gauthier (Co-supervisor)