Investigation of Liner Characteristics in the NASA Langley Curved Duct Test Rig

15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)

et al. 2009

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The Curved Duct Test Rig (CDTR) has been developed to investigate sound propagation through a duct of size comparable to the aft bypass duct of typical aircraft engines. The axial dimension of the bypass duct is often curved and this geometric characteristic is captured in the CDTR. The semiannular bypass duct is simulated by a rectangular test section in which the height corresponds to the circumferential dimension and the width corresponds to the radial dimension.

Section: Introductionmentioning

confidence: 99%

Advanced Computational and Experimental Techniques for Nacelle Liner Performance Evaluation

15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)

et al. 2009

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“…This liner was designed to provide the maximum attenuation in the middle of the useable frequency range (~1500 Hz) and at the maximum flow speed (Mach 0.275) of the CDTR at the time. The authors reported on evaluations of this in-house-designed liner (Liner L01) in a previous paper [2].…”

Section: Introductionmentioning

confidence: 99%

Report on Recent Upgrades to the Curved Duct Test Rig at NASA Langley Research Center

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)

et al. 2011

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The Curved Duct Test Rig (CDTR) is an experimental facility that is designed to assess the acoustic and aerodynamic performance of aircraft engine nacelle liners in close to full scale. The test section is between 25% and 100% of the scale of aft bypass ducts of aircraft engines ranging in size from business jet to large commercial passenger jet. The CDTR has been relocated and now shares space with the Grazing Flow Impedance Tube in the Liner Technology Facility at NASA Langley Research Center. As a result of the relocation, research air is supplied to the CDTR from a 50,000 cfm centrifugal fan. This new air supply enables testing of acoustic liner samples at up to Mach 0.500. This paper documents experiments and analysis on a baseline liner sample, which the authors had analyzed and reported on prior to the move to the new facility. In the present paper, the experimental results are compared to those obtained previously in order to ensure continuity of the experimental capability. Experiments that take advantage of the facility's expanded capabilities are also reported. Data analysis features that enhance understanding of the physical properties of liner performance are introduced. The liner attenuation is shown to depend on the mode that is incident on the liner test section. The relevant parameter is the mode cut-on ratio, which determines the angle at which the sound wave is incident on the liner surface. The scattering of energy from the incident mode into higher order, less attenuated modes is demonstrated. The configuration of the acoustic treatment, in this case lined on one surface and hard wall on the opposite surface, is shown to affect the mode energy redistribution.

“…In a previous paper 13 the authors outlined the procedure by which sound measured at the duct walls is used to determine the complex amplitudes of the modes. The modal amplitudes are used to determine the sound pressure and acoustic velocity of each modal component in a method outlined in a previous paper by the authors 14 . The sound pressure p mn and acoustic velocity u mn are used to evaluate Morfey's 15 expression for the axial acoustic intensity of the (m,n) modal component, I mn , in uniform axial flow:…”

Section: A Attenuation Computation From Measured Datamentioning

confidence: 99%

“…Figure 1 is a photograph of the Curved Duct Test Rig. A brief description of the test rig will be presented here, and more complete description of the rig can be found in previous papers by the authors 13,14 . Air is supplied to the test rig from a centralized air supply and passes through a set of mufflers (not shown in the photograph), an elbow with turning vanes, and a flow conditioning section to smooth the air flow and reduce turbulence.…”

Section: Introductionmentioning

confidence: 99%

Configuration Effects on Acoustic Performance of a Duct Liner

14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)

et al. 2008

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Continued success in aircraft engine noise reduction necessitates ever more complete understanding of the effect that flow path geometry has on sound propagation in the engine. The Curved Duct Test Rig (CDTR) has been developed at NASA Langley Research Center to investigate sound propagation through a duct of comparable size (approximately ½ the gap of GE90) and physical characteristics to the aft bypass duct of typical aircraft engines. The liner test section is designed to mimic the outer/inner walls of an engine exhaust bypass duct that has been unrolled circumferentially. Experiments to investigate the effect of curvature along the flow path on the acoustic performance of a test liner are performed in the CDTR and reported in this paper. Flow paths investigated include both straight and curved with offsets from the inlet to the discharge plane of ½ and 1 duct width, respectively. The test liners are installed on the side walls of the liner test section. The liner samples are perforate over honeycomb core, which design is typical of liners installed in aircraft nacelles. In addition to fully treated side walls, combinations of treated and acoustically rigid walls are investigated. While curvature in the hard wall duct is found not to reduce the incident sound significantly, it does cause mode scattering. It is found that asymmetry of liner treatment causes scattering of the incident mode into less attenuated modes, which degrades the overall liner attenuation. It is also found that symmetry of liner treatment enhances liner performance by eliminating scattering into less attenuated modes. Comparisons of measured liner attenuation with numerical results predicted by an analytic model based on the parabolic approximation (CDUCT-LaRC) have also been made and are reported in this paper. The effect of curvature in the rigid wall configuration estimated by CDUCT-LaRC is similar to the observed results, and the mode scattering seen in the measurements also occurs in the analytic model results. The analytic model and experiment show similar differences of overall attenuation between one wall treated and both walls treated.