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Currie T.C.,National Research Council Canada | Currie T.C.,Gas Turbine Laboratory | Struk P.M.,NASA | Tsao J.-C.,Ohio Aerospace Institute | And 4 more authors.
4th AIAA Atmospheric and Space Environments Conference 2012 | Year: 2012

This paper describes experiments performed in an altitude chamber at the National Research Council of Canada (NRC) as the first phase of a joint NRC/NASA program investigating ice crystal accretion in aero engines. The principal objective was to explore the effect of wet bulb temperature Twb (dependent on air temperature, humidity and pressure) on accretion behavior, since preliminary results published in an earlier paper indicated that well-adhered accretions are only possible at Twb<0°C, when water in an impinging mixedphase flow can freeze to a surface. To assess the accretion sensitivity to Twb, the symmetrical airfoil used in the previous work was tested at pressures of 44.8 kPa and 93kPa, usually at 0.25 Mach number, over a range of freestream liquid water and ice water concentrations, total air temperatures and humidity levels. Twb was typically maintained at +2°C or -2°C, based on dry total conditions (i.e. without ice or water injection). Total air temperature was >0°C in all tests. The limited test results confirmed that accretion behavior is very sensitive to Twb, which is in turn strongly related to pressure since evaporative cooling increases with decreasing pressure. Humidity and total temperature did not appear to have an independent effect on accretion behavior. Accretions, often resembling glaze ice, formed at Twb<0°C, when freestream water would freeze on the test airfoil without ice crystals present in the freestream. At Twb>0°C ice deposits were observed to be slushy, poorly adhered and shed frequently. The size of such deposits appeared to be a non-linear function of the freestream ice water content (IWC), becoming much larger at high IWC. © 2012 by National Research Council of Canada. Published by the American Institute of Aeronautics and Astronautics, Inc. Source


Ng L.W.T.,Massachusetts Institute of Technology | Ng L.W.T.,Gas Turbine Laboratory | Spakovszky Z.,Massachusetts Institute of Technology | Spakovszky Z.,Gas Turbine Laboratory
AIAA Journal | Year: 2011

This paper presents a method based on the Kirchhoff diffraction theory to predict the shielding of turbomachinery noise by the airframe of an advanced aircraft configuration. The key feature of this method is the fast computational time, even at very high frequencies, which makes it a useful tool to rapidly assess the noise footprint of an aircraft design. The offline part preprocesses the three-dimensional shielding geometry into a contour of its outline based on the source line of sight. Given this contour, the online part calculates the noise attenuation at a particular observer location and source frequency and can be called multiple times by an aircraft noise prediction program to add shielding estimates to its effective perceived noise level calculations. This method is most accurate for flat shielding objects characterized by edge-diffraction rays, rather than smooth, rounded objects characterized by creeping rays; shielding differences of up to 3 dB were observed in calculations using a sphere and a disk. Finally, the method is applied to a hybrid wing-body aircraft to assess and quantify the noise shielding benefit of its large planform area. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Source


Hileman J.I.,Massachusetts Institute of Technology | Hileman J.I.,Gas Turbine Laboratory | Spakovszky Z.S.,Massachusetts Institute of Technology | Spakovszky Z.S.,Gas Turbine Laboratory | And 4 more authors.
Journal of Aircraft | Year: 2010

The noise goal of the Silent Aircraft Initiative, a collaborative effort between the University of Cambridge and Massachusetts Institute of Technology, demanded an airframe design with noise as a prime design variable and a design philosophy that cut across multiple disciplines. This paper discusses a novel design methodology synthesizing first-principles analysis and high-fidelity simulations, and it presents the conceptual design of an aircraft with a calculated noise level of 62 dBA at the airport perimeter. This is near the background noise in a well-populated area, making the aircraft imperceptible to the human ear on takeoff and landing. The all-lifting airframe of the conceptual aircraft design also has the potential for improved fuel efficiency, as compared with existing commercial aircraft. A key enabling technology in this conceptual design is the aerodynamic shaping of the airframe centerbody. Design requirements and challenges are identified, and the resulting aerodynamic design is discussed in depth. The paper concludes with suggestions for continued research on enabling technologies for quiet commercial aircraft. Copyright © 2010 by the authors. Source


Shah P.N.,Massachusetts Institute of Technology | Shah P.N.,Gas Turbine Laboratory | Mobed D.,Massachusetts Institute of Technology | Mobed D.,Gas Turbine Laboratory | And 4 more authors.
AIAA Journal | Year: 2010

Aircraft on approach in high-drag, high-lift configurations create inherently noisy flow structures. For flaps, slats, and undercarriage, the strong correlation between overall noise and drag suggests that future quiet aircraft will need to generate drag at low noise levels. This paper presents a novel noise-reduction concept based on the idea that appreciable pressure drag can be generated by a relatively quiet swirling exhaust flow. A first aeroacoustic assessment of ram-pressure-driven swirling exhaust flows and their associated vortex breakdown instability is presented. The technical approach combines 1) an in-depth aerodynamic analysis, 2) qualitative acoustic source descriptions via plausibility arguments, and 3) detailed quantitative phased microphone-array measurements of a model-scale engine nacelle with stationary swirl vanes at a full-scale approach Mach number of 0.17. The analysis shows an acoustic signature composed of 1) quadrupole-type turbulent mixing noise in the swirling core flow and 2) scattering noise from vane boundary layers and turbulent eddies of the burst vortex structure near the nacelle, pylon, and vane centerbody trailing edges. The highest stable swirl-angle setting yields a nacelle-area-based drag coefficient of 0.83 with a full-scale overall sound pressure level of about 40 dBA at the International Civil Aviation Organization approach certification point. Copyright © 2009 by P. N. Shah, D. Mobed, Z. S. Spakovszky, T. F. Brooks, and W. M. Humphreys Jr. Source


Knezevici D.C.,National Research Council Canada | Knezevici D.C.,Gas Turbine Laboratory | Fuleki D.,National Research Council Canada | Fuleki D.,Gas Turbine Laboratory | And 4 more authors.
4th AIAA Atmospheric and Space Environments Conference 2012 | Year: 2012

This paper describes the commissioning of a new test apparatus intended to simulate an inner-compressor duct bleed slot. It also identifies, for the first time, that ice crystal particle size plays an important role in the ice crystal phenomenon. Data and sample images of accretion are presented for wet bulb temperatures near freezing. The effect of wet bulb temperature and particle size on the natural melting of ice crystals is investigated. In addition, the erosion of surface accretion by ice crystal particles is discussed. © 2012 by Her Majesty the Queen in Right of Canada. Published by the American Institute of Aeronautics and Astronautics, Inc. Source

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