A parametric investigation of tip injection for active tip vortex control

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2010
Dedekargınoğlu, Rıza Can
Wing tip vortex is a challenging phenomenon that reduces the lift generation at the tip region of the wing. For aerial vehicles, several methodologies were presented for the sake of controlling vortices and alleviating effects of tip loss. In this study, the effect of wing tip injection on wing tip vortex structure was investigated computationally. A NACA0015 profile rectangular wing was employed with an aspect ratio of 3, at a free stream Reynolds number of 67000. 10 identical ejection holes along the wing were prepared chordwise to provide cross sectional air flow in order to determine the net effect of ejection over wing tip vortices and wake flow field. Study setup consists of a wind tunnel that is 1.6m long, 0.6m wide and 0.6m high, which the wing is attached to one side of it as a cantilever beam. Chord length of the wing is 0.1m and span is 0.3m. A constant free stream air flow is maintained with 10 m/s of velocity. Computer aided drawing (CAD) and grid generation were carried out using commercial tools. Whole setup was drawn using Rhinoceros. Surface mesh was created using ANSYS Gambit, ANSYS T-Grid software was used for generating the viscous mesh over the wing and finally for volume mesh ANSYS Gambit was utilized once more. FLUENT was chosen to be the flow solution tool with k-ω SST turbulence model. For 3 different angles of attack cases, respectively, 4°, 8° and 12°, several injection scenarios were defined. There are 3 steady injection cases for each angle of attack case namely, no injection case, uniform injection case, triangular waveform injection case where there is no injection at the leading edge tip whereas there is injection which is equal to the uniform injection velocity at the trailing edge tip. Moreover there are 5 additional scenarios for 8° angle of attack case that are, sinusoidal waveform injection case which consists of a chordwise velocity distribution shape that is a quarter sinus wave where maximum injection velocity is the same as the uniform velocity, reverse triangular waveform injection case where injection velocities were reversed with respect to triangular waveform case, two cases consisting of angled injections having both +15° and -15° with respect to the flapping axis of the wing. The effect of tube walls on the jet injection was neglected for all cases, therefore for the last case, in order to simulate pipe flow, a case is provided with uniform injection velocity. In that way, regardless of the solution method, a parametric study was performed. Considering each case, non-dimensional 3-axis velocity components, turbulent kinetic energy, vorticity magnitude, pressure, lift and drag values were computed and having the exactly same cases as an experimental study for 8° angle of attack, a comparison of aerodynamic data series was presented. As results, it’s observed that, vortex core locations were shifted upwards and away from the tip region. Increasing the turbulence level of the tip flow by tip injection, inherently the pressure difference became larger, however as the vortices ascend, tip loss decreases. In that way, a significant increase in the lift was observed while drag values are slightly increased, as well.
Citation Formats
R. C. Dedekargınoğlu, “A parametric investigation of tip injection for active tip vortex control,” M.S. - Master of Science, Middle East Technical University, 2010.