Optimizing Max Camber Points Along Thin Triangular Airfoils for Higher Lift/Drag Ratios

The purpose of this report is to expand knowledge on the lift and drag properties of thin triangular airfoils, and determine whether or not they are a viable option for low-Reynolds number applications. Thin triangular airfoils were thought to be more efficient than standard NACA airfoils under specific conditions. This experiment was performed through the wind tunnel testing of a NACA 2412 and nine thin triangular airfoils with varying max camber points. Between the Reynolds numbers of 30-42,000, lift and drag values were collected at varying angles of attack. Overall, it was found that the thin triangular airfoils proved to have unique lift and drag characteristics when compared to the standard NACA 2412

Emergence of turbulence in an oscillating Bose-Einstein condensate

We report on the experimental observation of vortices tangle in an atomic BEC of Rb-87 atoms when an external oscillatory perturbation is introduced in the trap. The vortices tangle configuration is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud has suppression of the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion. Instead, the cloud expands keeping the ratio between their axis constant. Turbulence in atomic superfluids may constitute an alternative system to investigate decay mechanisms as well as to test fundamental theoretical aspects in this field.Comment: accepted for Phys. Rev. Let

Generation of vortices and observation of Quantum Turbulence in an oscillating Bose-Einstein Condensate

We report on the experimental observation of vortex formation and production of tangled vortex distribution in an atomic BEC of Rb-87 atoms submitted to an external oscillatory perturbation. The oscillatory perturbations start by exciting quadrupolar and scissors modes of the condensate. Then regular vortices are observed finally evolving to a vortex tangle configuration. The vortex tangle is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud has suppression of the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion.Comment: to appear in JLTP - QFS 200

Route to turbulence in a trapped Bose-Einstein condensate

We have studied a Bose-Einstein condensate of $^{87}Rb$ atoms under an oscillatory excitation. For a fixed frequency of excitation, we have explored how the values of amplitude and time of excitation must be combined in order to produce quantum turbulence in the condensate. Depending on the combination of these parameters different behaviors are observed in the sample. For the lowest values of time and amplitude of excitation, we observe a bending of the main axis of the cloud. Increasing the amplitude of excitation we observe an increasing number of vortices. The vortex state can evolve into the turbulent regime if the parameters of excitation are driven up to a certain set of combinations. If the value of the parameters of these combinations is exceeded, all vorticity disappears and the condensate enters into a different regime which we have identified as the granular phase. Our results are summarized in a diagram of amplitude versus time of excitation in which the different structures can be identified. We also present numerical simulations of the Gross-Pitaevskii equation which support our observations.Comment: 6 pages, 3 figure

Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length

We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by modulating the atomic scattering length via a Feshbach resonance. Excitation occurs at various modulation frequencies, and resonances located at the natural quadrupole frequency of the condensate and at the first harmonic are observed. We also investigate the amplitude of the excited mode as a function of modulation depth. Numerical simulations based on a variational calculation agree with our experimental results and provide insight into the observed behavior.Comment: Submitted to PR