39,435 research outputs found
Reduced dimension modeling of leading edge turbulent interaction noise
No full textA computational aeroacoustics approach is used to model the effects of real airfoil geometry on leading edge turbulent interaction noise for symmetric airfoils at zero angle of attack. For the first time, one-component (transverse), two-component (transverse and streamwise), and three-component (transverse, streamwise, and spanwise) synthesized turbulent disturbances are modeled instead of single frequency transverse gusts, which previous computational studies of leading edge noise have been confined to. The effects of the inclusion of streamwise and spanwise disturbances on the noise are assessed, and it is shown that accurate noise predictions for symmetric airfoils can be made by modeling only the transverse disturbances, which reduces the computational expense of simulations. Additionally, the two-component turbulent synthesis method is used to model the effects of airfoil thickness on the noise for thicknesses ranging from 2% to 12%. By using sufficient airfoil thicknesses to show trends, it is found that airfoil thickness will reduce the noise at high frequency, and that the sound power P will reduce linearly with increasing airfoil thickness
Effects of real airfoil geometry on leading edge gust interaction noise
No full textHigh-order computational aeroacoustic methods are applied to the modeling of noise due to interactions between gusts and the leading edge of real symmetric airfoils. The effects of airfoil thickness and leading edge radius on noise are investigated systematically and in-dependently for the first time, at higher frequencies than previously used in computational methods. Single frequency harmonic gusts are interacted with airfoils of varying geometry at zero angle of attack. Increases in both leading edge radius and thickness are found to reduce the predicted noise. This noise reduction effect becomes greater with increasing frequency and Mach number. The dominant noise reduction mechanism for airfoils with real geometry is found to be related to the leading edge stagnation region. The assumption of uniform meanflow is shown to be invalid when modeling the leading edge noise of real airfoils. However, accurate results are still obtained when an inviscid meanflow is assumed. The accuracy of analytic flat plate solutions can be expected to decrease with increasing airfoil thickness, leading edge radius, gust frequency and Mach number
Including wall effects in analytical leading edge noise predictions
No full textAn analytical solution to leading-edge noise produced by a translating two-dimensional flat plate ingesting turbulence in proximity to a hard-wall is presented. This is a relevant problem to calculate the installation noise of open rotors and un-ducted fans. The analytical solution to the problem is given by using Amiet’s flat plate theory in conjunction with the Method Of Images (MOI) to include the effects of the wall. The low frequency, low Mach number limit of the analytical solution is investigated and it is shown that the flat plate in this limit behaves like a compact vertical dipole. The analytical solution is verified by a Computational AeroAcoustic (CAA) simulation that also uses the MOI to simulate a wall. While the MOI gives an approximation of the wall, it does not model all of the effects, such as diffraction from the edges of the flat plate and acoustic shielding due to the presence of the flat plate. These effects, which are ignored in the MOI are quantified using a CAA simulation that models the wall using a hard-slip-wall boundary condition. It is found that the analytical predictions and the CAA simulations using the MOI compare well. However, when the MOI is compared to the CAA simulation using a hard-slip-wall boundary condition, it is found that the MOI does not capture the effect of the shadow zone that is created due to the shielding effect of the aerofoil. The extent of the shadow zone is modified by changing the height of the aerofoil from the wall, and it shown that as the height of the aerofoil from the wall is increased, the shielding effect decreases
Synthetic turbulence methods for leading edge noise predictions
No full textAn advanced digital filter method to generate synthetic turbulence is presented for efficient two- and three-dimensional leading edge noise predictions. The technique, which is based on the Random Particle-Mesh method, produces a turbulent inflow that matches a target isotropic energy spectrum. The discretized equations for the synthetic eddies, and the input parameters needed to recover the desired turbulence statistics, are presented. Moreover, a simple and fast implementation strategy, which does not require an additional boundary condition, is presented under the frozen turbulence assumption. The method is used in a linearized Euler solver to predict turbulence-airfoil interaction noise from a number of configurations, including variations in airfoil thickness, angle of attack and Mach number. For the first time, noise predictions from a digital filter method are directly compared to those provided by synthetic turbulence based on a summation of Fourier modes. The comparison indicates that the advanced digital filter method gives enhanced performance in terms of computational cost and simulation accuracy. In addition, initial tests show that this method is capable of reproducing experimental noise measurements within 3 dB accuracy
Leading edge noise predictions using anisotropic synthetic turbulence
No full textAn advanced digital filter method is presented to generate divergence-free synthetic turbulence with homogeneous anisotropic velocity spectra. The resulting fluctuating velocity field is obtained through a superposition of anisotropic Gaussian eddies. This method is used to generate a two-dimensional turbulent flow with the key statistics of homogeneous axisymmetric turbulence. This type of turbulence has been reported in aero-engine intakes, fan wakes and open-jet wind tunnel experiments. The advanced digital filter method is implemented in a linearized Euler solver in order to investigate potential effects of anisotropic turbulence on leading edge noise. Computational aeroacoustic simulations are performed for anisotropic turbulence with streamwise-to-transverse length scale ratios ranging from 0.33 to 3 on a number of isolated airfoil configurations, including variations in mean flow Mach number, airfoil thickness and angle of attack. Noise reduction due to airfoil thickness is assessed on a NACA 0012 airfoil at zero angle of attack, showing similar trends for bothisotropic and moderately anisotropic turbulent flows. Effects of anisotropic turbulence on noise become evident for airfoil configurations at non-zero angle of attack
Antoine Thomas. Nouveaux essais de philologie française
No full textLanglois Ernest. Antoine Thomas. Nouveaux essais de philologie française. In: Bibliothèque de l'école des chartes. 1905, tome 66. p. 313
Kselman (Thomas A.) Miracles and Prophecies in Nineteenth- Century France
No full textLanglois Claude. Kselman (Thomas A.) Miracles and Prophecies in Nineteenth- Century France. In: Archives de sciences sociales des religions, n°64/2, 1987. pp. 294-295
Kselman (Thomas A.) Miracles and Prophecies in Nineteenth- Century France
No full textLanglois Claude. Kselman (Thomas A.) Miracles and Prophecies in Nineteenth- Century France. In: Archives de sciences sociales des religions, n°64/2, 1987. pp. 294-295
Joseph Crespino Interviews Thomas Mullen, Author of Darktown
No full textHistorian Joseph Crespino interviews Decatur, Georgia-based historical novelist, Thomas Mullen, author of Darktown (New York: Simon and Schuster, 2016), The Revisionists (London: Hodder & Stoughton, 2011), The Many Deaths of the Firefly Brothers (New York: Random House, 2010), and The Last Town on Earth (New York: Random House, 2006)
Thomas Naef, Holy Bits. A Guide for Using Computers in Biblical Scholarship, Piscataway, Gorgias Press, 2009
No full textLanglois Michaël. Thomas Naef, Holy Bits. A Guide for Using Computers in Biblical Scholarship, Piscataway, Gorgias Press, 2009. In: Revue d'histoire et de philosophie religieuses, 91e année n°2, Avril-Juin 2011. pp. 274-275
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