311 resultados para Turbulence.
Resumo:
Turbulence, as naturally occurs in the atmosphere, is known to become highly anisotropic in the presence of the flow induced by a propeller. This turbulent distortion, caused by the streamtube contraction, significantly affects the tonal content of the radiated noise due to turbulence ingestion. We present here an analytic framework in which turbulent distortion may be assessed for any irrotational mean flow which approaches uniform axial flow far upstream. Sound spectra are presented for the case of two rotors in close proximity, for which the distortion is asymmetric. Quantities such as the turbulence spectrum at the rotor face and sound directivity then vary with azimuthal angle φ. © 2010 by Rosalyn A.V. Robison & N. Peake.
Resumo:
A direct comparison between time resolved PLIF measurements of OH and two dimensional slices from a full three dimensional DNS data set of turbulent premixed flame kernels in lean methane/air mixture was presented. The local flame structure and the degree of flame wrinkling were examined in response to differing turbulence intensities and turbulent Reynolds numbers. Simulations were performed using the SEGA DNS code, which is based on the solution of the compressible Navier Stokes, species, and energy equations for a lean hydrocarbon mixture. For the OH PLIF measurements, a cluster of four Nd:YAG laser was fired sequentially at high repetition rates and used to pump a dye laser. The frequency doubled laser beam was formed into a sheet of 40 mm height using a cylindrical telescope. The combination of PLIF and DNS has been demonstrated as a powerful tool for flame analysis. This research will form the basis for the development of sub-grid-scale (SGS) models for LES of lean-premixed combustion systems such as gas turbines. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).
