We report atmospheric turbulence parameters, namely atmospheric seeing, tilt-anisoplanatic angle (θ
0) and coherence time (τ
0), measured under various sky conditions, at Vainu Bappu Observatory in Kavalur. Bursts of short exposure images of selected stars were recorded with a high-speed, frame-transfer CCD mounted on the Cassegrain focus of a newly commissioned 1.3 m telescope. The estimated median seeing is ≈ 1.85″ at wavelength of ∼ 600 nm, the image motion correlation between different pairs of stars is ∼ 44% for θ
0 ≈ 36″ and mean τ
0 is ≈ 2.4 ms. This work was motivated by the design considerations and expected performance of an adaptive optics system that is currently being planned for the telescope.
Low-speed subsonic jets are commonly encountered in many flow systems such as in chimney exhausts, impinging jets, inlets in combustors of diesel engines and gas turbines. Large-eddy simulation of a Mach 0.1, three-dimensional plane (square) turbulent air jet was performed. The Reynolds number of the jet based on the jet width was 3 × 10 4 . The width of the jet was 0.013 m. The aim of the present work was to develop a threedimensional compressible parallel LES finite-volume code and validate it against an experimental free jet test case. A robust novel numerical scheme based on the blending of Riemann invariants and the exact Godunov solver, capable of handling low Mach number flows without preconditioning, was used. The Smagorinsky sub-grid scale model was used to model the unresolved stresses. An investigation was carried out into the self similarity behavior of the jet and the two-point correlations and the dissipation was computed. It is observed that istropicity of turbulence only exists in the v and w components and self-similar behavior was observed approximately beyond 90 jet widths downstream.
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