The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Ramon Reba - One of the best experts on this subject based on the ideXlab platform.
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Using Reynolds-Averaged Navier-Stokes Calculations to Predict Trailing-Edge Noise
AIAA Journal, 2010Co-Authors: Stewart A. L. Glegg, Bruce L. Morin, Oliver Atassi, Ramon RebaAbstract:This paper describes a method for using Reynolds-averaged Navier―Stokes calculations of the flow over an airfoil to calculate far-field sound spectra generated by boundary-layer Turbulence interacting with the airfoil trailing edge. It is shown that a model of the spatial distribution of turbulent kinetic energy in a boundary-layer flow can be related to an integral of the local Turbulence Spectrum multiplied by a function of the mean flow velocity distribution. Inverting this relationship gives the Turbulence Spectrum required for calculations of the pressure on the surface beneath the boundary layer, hence the far-field sound radiated from a turbulent boundary layer interacting with a sharp trailing edge. Results are presented showing estimates of surface pressure spectra and radiated sound from a turbulent boundary layer flowing over the sharp trailing edge of a NACA 0012 airfoil, and they are compared with measurements of airfoils with different chord and Reynolds numbers. Also shown are predictions based on this approach for the self-noise from a 22 in. fan. The measured and predicted far-field sound spectra were found to show the same dependence on flow speed and close agreement in absolute level.
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Using RANS Calculations of Turbulent Kinetic Energy to Provide Predictions of Trailing Edge Noise
14th AIAA CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008Co-Authors: Stewart A. L. Glegg, Bruce L. Morin, Oliver Atassi, Ramon RebaAbstract:This paper describes a method for using RANS calculations of the flow over an airfoil to calculate far field sound spectra generated by boundary layer Turbulence interacting with the airfoil trailing edge. It will be shown that a model of the spatial distribution of turbulent kinetic energy in a boundary layer flow can be related to an integral of the local Turbulence Spectrum multiplied by a function of the mean flow velocity distribution. Inverting this relationship gives the Turbulence Spectrum required for calculations of the pressure on the surface beneath the boundary layer and hence the far field sound radiated from a turbulent boundary layer interacting with a sharp trailing edge. Results will be presented showing estimates of surface pressure spectra and radiated sound from a turbulent boundary layer flowing over the sharp trailing edge of a NACA 0012 airfoil, and compared to measurements of airfoils with different chord and Reynolds numbers. Also shown are predictions based on this approach for the self noise from a 22 inch fan. The measured and predicted far field sound spectra were found to show the same dependence on flow speed and close agreement in absolute level.
Vladimir P Lukin - One of the best experts on this subject based on the ideXlab platform.
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Approximations of the synoptic spectra of atmospheric Turbulence by sums of spectra of coherent structures
Proceedings of SPIE, 2015Co-Authors: Victor V. Nosov, Vladimir P Lukin, Eugene V. Nosov, A. V. TorgaevAbstract:It is shown that the known experimental synoptic spectra of the atmospheric Turbulence (Spectrum of Van der Hoven, 1957; Spectrum of Kolesnikova, Monin, 1965) represent the sum of the solitary spectra of coherent structures with various sizes (with variety outer scales).
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Investigation of the anisotropy of the atmospheric Turbulence Spectrum in the low frequency range
IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium, 1996Co-Authors: Vladimir P LukinAbstract:This paper deals with the analysis of optical measurements data on the atmospheric Turbulence characteristics. Some conclusions are drawn on the variability of the most large scale component of the turbulent inhomogeneities, Spectrum for the atmosphere as a whole and for the boundary layer as well. The author analyzes several years' experimental studies.
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Investigation of the anisotropy of the atmospheric Turbulence Spectrum in the low-frequency range
Atmospheric Propagation and Remote Sensing IV, 1995Co-Authors: Vladimir P LukinAbstract:This paper deals with the analysis of optical measurements data on the atmospheric Turbulence characteristics. Some conclusions are drawn on the variability of the most large scale component of the turbulent inhomogeneities, Spectrum for the atmosphere as a whole and for the boundary atmospheric layer as well.
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comparison of models of the atmospheric Turbulence Spectrum
SPIE's International Symposium on Optical Engineering and Photonics in Aerospace Sensing, 1994Co-Authors: Vladimir P LukinAbstract:This paper deals with theoretical and experimental studies of optical waves that compare different models of the atmospheric Turbulence spectra. For inhomogeneous optical paths in the atmosphere we introduce the term the Turbulence Spectrum averaged over the path and present an analysis of some models of spectral density of the refractive index fluctuations for the turbulent atmosphere. The models are compared on the basis of calculation and measurements of statistical characteristics of phase fluctuations of optical waves propagating in the turbulent atmosphere.
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Optical measurements of the outer scale of the atmospheric Turbulence
Proceedings of SPIE, 1993Co-Authors: Vladimir P LukinAbstract:The atmospheric Turbulence Spectrum even in the surface layer differ by the larger dynamical range and, in accordance with it, in view of the finite correctness of the optical measurements by themselves, cannot be reconstructed from the measuring of any one of the optical wave parameters. Measurements of the fluctuations of the optical wave phase can be used for investigation of the energy range of the Turbulence Spectrum.
E. Mazzucato - One of the best experts on this subject based on the ideXlab platform.
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Reflectometer measurements of density fluctuations in tokamak plasmas (invited)
Review of Scientific Instruments, 1995Co-Authors: R. Nazikian, E. MazzucatoAbstract:Many anomalous features observed in reflectometer measurements of turbulent fluctuations in tokamak plasmas, such as loss of coherent reflection, large amplitude fluctuations, large angular divergence of the reflected waves, and correlation lengths of the order of the free‐space wavelength of the probe beam, can be explained by modeling the plasma fluctuations as a poloidally varying random phase grating located at the cutoff with a phase magnitude given by 1D geometric optics. A key result of this analysis is that the Turbulence Spectrum cannot be inferred from phase measurements when large amplitude fluctuations are observed at the receiver. However, the Turbulence Spectrum may still be recovered from phase measurements by use of imaging optics and wide angle phase sensitive receivers.
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Reflectometer measurements of density fluctuations in tokamak plasmas
Review of Scientific Instruments, 1994Co-Authors: R. Nazikian, E. MazzucatoAbstract:We show that many anomalous features observed in reflectometer measurements of turbulent fluctuations in tokamak plasmas, such as loss of coherent reflection, large amplitude fluctuations, large angular divergence of the reflected waves and correlation lengths of the order of the free space wavelength of the probe beam, can be explained by modeling the plasma fluctuations as a poloidally varying random phase grating located at the cutoff with a phase magnitude given by 1D geometric optics. A key result of our analysis is that the Turbulence Spectrum cannot be inferred from phase measurements when large amplitude fluctuations are observed at the receiver. However, the Turbulence Spectrum may still be recovered from phase measurements by use of imaging optics, and wide angle phase sensitive receivers.
J. K. Harmon - One of the best experts on this subject based on the ideXlab platform.
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The solar wind Turbulence Spectrum near the sun
AIP Conference Proceedings, 2008Co-Authors: A. Coles, J. K. HarmonAbstract:The results of recent radio propagation observations of the near‐Sun solar wind are reported. The new results, derived from radar spectral broadening and VLBI phase scintillations, are compared with earlier observations (angular broadening, spacecraft spectra broadening, intensity scintillation, and phase scintillation) to determine the shape and radial evolution of the power Spectrum of plasma density fluctuations. The various data are best reconciled by a Turbulence Spectrum which is relatively steep (Kolmogorov) at large scales (≳103 km), has a local flattening at intermediate (10–100 km) scales, and steepens again at the inner (cutoff) scale.
P. K. Manoharan - One of the best experts on this subject based on the ideXlab platform.
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Amplitude of solar wind density Turbulence from 10 to 45 R
Journal of Geophysical Research, 2016Co-Authors: K. Sasikumar Raja, P. K. Manoharan, Madhusudan Ingale, R. Ramesh, Prasad Subramanian, P. JanardhanAbstract:We report on the amplitude of the density Turbulence Spectrum ( CN2) and the density modulation index (δN/N) in the solar wind between 10 and 45R⊙. We derive these quantities using a structure function that is observationally constrained by occultation observations of the Crab nebula made in 2011 and 2013 and similar observations published earlier. We use the most general form of the structure function, together with currently used prescriptions for the inner/dissipation scale of the Turbulence Spectrum. Our work yields a comprehensive picture of a) the manner in which CN2 and δN/N vary with heliocentric distance in the solar wind and b) of the solar cycle dependence of these quantities.
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Evolution of Near-Sun Solar Wind Turbulence
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: P. K. ManoharanAbstract:This paper presents a preliminary analysis of the Turbulence Spectrum of the solar wind in the near-Sun region R < 50R⊙, obtained from interplanetary scintillation measurements with the Ooty Radio Telescope at 327 MHz. The results clearly show that the scintillation is dominated by density irregularities of size about 100–500km. The scintillation at the small-scale side of the Spectrum, although significantly less in magnitude, has a flatter Spectrum than the larger-scale dominant part. Furthermore, the spectral power contained in the flatter portion rapidly increases closer to the Sun. These results on the Turbulence Spectrum forR < 50R⊙ quantify the evidence for radial evolution of the small-scale fluctuations (≤50 km) generated by Alfven waves.
