Session: 01-10-01: Congress-Wide Symposium on NDE & SHM: Ultrasonic Waves for Material Characterization and Damage Assessment

Paper Number: 96515

96515 - Variation of Sound Directivity From a Supersonic Nacelle 

The effects of aircraft flight speed and fan face pressure variations on sound propagation from an axisymmetric commercial supersonic engine inlet were studied using numerical methods. A parametric study was conducted, varying the free stream Mach number from 0.35 to 0.55 in increments of 0.0125, and the fan face back pressures from -10 kPa to -40 kPa in increments of 1 kPa, for a total of over 500 simulations. Parameter ranges were chosen to represent conditions which would be experienced during a supersonic transport's ascent or descent from cruising altitude. The fan face back pressure parameter represents the varying amount of suction that the engine fan could be providing. Adjusting this parameter changes the flow velocity through the annulus as well as the mass flow into the unit.  The parametric study was conducted on the geometry of a supersonic engine inlet for the LM 1044-X, an aircraft being jointly designed by Lockheed Martin and NASA as a concept study. A computational fluid dynamics (CFD) model of the inlet which was constructed in Ansys Fluent and used to obtain steady state compressible flow field results for each of these iterations. These results were then interpolated onto a model built in the acoustic solver ACTRAN which was used to create radiated noise transfer functions for each set of parameters run in the CFD model. One hundred twenty (120) far field receiver positions were placed so that it could be determined how much of the radiated energy coming from the unit was traveling along its axis, and how much was traveling off-axis towards the ground. It was observed that varying the fan face back pressure had a greater effect on the character of the resulting flow field than varying the freestream mach number, resulting in steeper gradients in air density, flow velocity, and local speed of sound. These changes in the flow field created differences in the radiated noise calculations of as much as 5 dB in certain frequency ranges. In general, it was observed that off-axis radiation decreased as freestream Mach number increased or as fan face gauge pressure decreased. Though broad trends were observable in the radiation data due to changes in both variables, it was shown that fan face gauge pressure has a greater impact on radiated noise than freestream Mach number. When frequency was fixed, and a two-dimensional map of the parameters was made, interesting features, such as bands and pockets of greater and lesser radiation appeared in the data, in addition to broad trends. Sets of mean flow parameters which provide the least sound transmission from the engine unit to observers on the ground are determined from these 2-D parameter contour maps.

Presenting Author: Mitchell Sugar University of Hartford

Presenting Author Biography: Mitchell Sugar is a graduate mechanical engineering student at the University of Hartford, currently pursuing a Masters of Science in mechanical engineering. He graduated with a Bachelors of Science in Engineering with a major in Acoustics in 2019 and then worked at General Dynamics Electric Boat for 2 years, where he built structural acoustics model for the ships signatures department. His academic interests include unsteady aerodynamics, hydroacousics, aeroacoustics, and structural vibrations.

Authors:

Mitchell Sugar University of Hartford
Paul Slaboch University of Hartford