Browsing by Author "Sharma, Gautam"

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    Classroom Captain
    Bendelac, Noam; Bafna, Tanishq; Sharma, Gautam; Krishnappagari, Sai Sanath; Samala, Sindhu Vyshnavi; Atukuri, Sri Sai Asrith (2022-12-09)
    The recent rise in remote learning has presented challenges for both students and teachers. Detailed visual demonstrations of spatial and visual subjects like physics, chemistry, or geometry can be harder to get across to students on a two dimensional screen. Static diagrams are helpful but insufficient for showing motion, interaction, or change. Some 2D interactive diagrams exist, and they can be sufficient for some topics, while other topics require the full three dimensions. Finally, interactive diagrams can be out of sync between the students’ screens and the teacher’s screen, so when the teacher is pointing something out, the students may not see it. If the teacher shares their screen visuals instead, then the diagram is not interactive for students. Our project seeks to solve these problems by providing 3D interactive diagrams that can be synchronized between the teacher and the students. We developed an interactive 3D educational web application for students to learn physics and calculus under the guidance of teachers. Teachers are able to both guide students’ learning directly by controlling the interactive 3D diagram on students’ screens, and let students learn independently by giving them control over their screens.
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    Turbulence Measurements in Trailing Vortices for B.W.I. Noise Prediction
    Devenport, William J.; Glegg, Stewart A. L.; Sharma, Gautam (Virginia Polytechnic Institute and State University, 1992-06-01)
    Blade wake interaction (BWI) noise is the broadband noise generated by the ingestion of turbulent tip vortices into helicopter rotors. Prediction of BWI noise requires knowledge of the turbulence structure of the tip vortex. This report describes a joint investigation to measure that structure and incorporate the results into a noise prediction scheme. Measurements were performed on the tip vortex shed by a single rectangular NACA 0012 half wing placed in a wind tunnel test section. The properties of the vortex were studied for a range of angles of attack (2.5° to 7.5°) and chord Reynolds numbers (130000 to 530000). Initially the vortex was examined for stability and probe interference effects through flow visualization. Then detailed three-component velocity, turbulence and spectral measurements were made using multiple hot wires between 20 and 30 chordlengths downstream of the wing. These measurements show the flow to consist of a small axisymmetric core surrounded by a large non-axisymmetric region in which the wing wake forms a spiral around the core. In contrast to the results of previous workers, most of whom studied vortices generated by split wing configurations, there appeared to be little axisymmetric region of merged turbulent flow. Turbulence levels in the spiral wake decay with downstream distance. They also fall as the core is approached, presumably because of the effects of the increased straining and curvature on the turbulent structures here. Turbulence spectra measured in the wake are very similar in form, regardless of conditions and exact location, and bear a strong resemblance to a von Karman spectrum. At most conditions true turbulence levels in and immediately adjacent to the core are very low. Velocity fluctuations, however, are intense as a consequence of coherent lateral motions of the core and possible wave motions and instabilities travelling along it. Velocity autospectra in the core show the lateral motions to be anisotropic at very low frequencies and isotropic and mid frequencies. A large part of these motions may well be self induced. Circulation profiles in this region show Hoffman and Joubert's semi-logarithmic region, and in one case reveal the core to be fully developed. From the point of view of BWI noise prediction the flow measurements identify three sources of velocity fluctuations; low-frequency anisotropic core motions, mid-frequency isotropic core motions, and turbulence in the surrounding spiral wake. Estimates of the noise produced by these different frequency regimes show that it is the mid-frequency isotropic motions which is the most important mechanism for noise production, but the spectral shape and the predicted directionality for this mechanism are not in agreement with the measurements of BWI noise. The original noise-prediction scheme, based on the concept of a more turbulent vortex, has been shown to be the wrong basis for the correct description of the flow, but in spite of this the results are significantly better than those presented here. This suggests that the flow measured in the wind tunnel does not have the same turbulence upwash spectrum as that encountered by the helicopter rotor. One of the features of a real helicopter rotor which was not considered is the effect of a downstream blade upon the tip vortex. This may cause vortex bursting or alter the flow structure in the rotor disc plane in other ways. Measurements to evaluate this concept are planned for the future.