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| Author | : Viswanathan R. Vadari |
| Publisher | : |
| Total Pages | : 404 |
| Release | : 1997 |
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| Author | : |
| Publisher | : |
| Total Pages | : 98 |
| Release | : 2001 |
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| Author | : United States. National Aeronautics and Space Administration |
| Publisher | : |
| Total Pages | : |
| Release | : 2002* |
| Genre | : |
| ISBN | : |
| Author | : National Aeronautics and Space Administration (NASA) |
| Publisher | : Createspace Independent Publishing Platform |
| Total Pages | : 34 |
| Release | : 2018-06-24 |
| Genre | : |
| ISBN | : 9781721791934 |
An experimental proof-of-concept test was conducted to demonstrate reduction of rotor-stator interaction noise through the use of rotor-trailing edge blowing. The velocity deficit from the viscous wake of the rotor blades was reduced by injecting air into the wake from a continuous trailing edge slot. Hollow blades with interior guide vanes create flow channels through which externally supplied air flows from the blade root to the trailing edge. A previous paper documented the substantial tonal reductions of this Trailing Edge Rotor Blowing (TERB) fan. This report documents the broadband characteristics of TERB. The Active Noise Control Fan (ANCF), located at the NASA Glenn Research Center, was used as the proof-of-concept test bed. Two-component hotwire data behind the rotor, unsteady surface pressures on the stator vane, and farfield directivity acoustic data were acquired at blowing rates of 1.1, 1.5, and 1.8 percent of the total fan mass flow. The results indicate a substantial reduction in the rotor wake turbulent velocity and in the stator vane unsteady surface pressures. Based on the physics of the noise generation, these indirect measurements indicate the prospect of broadband noise reduction. However, since the broadband noise generated by the ANCF is rotor-dominated, any change in the rotor-stator interaction broadband noise levels is barely distinguishable in the farfield measurements. Sutliff, Daniel L. Glenn Research Center E-15171, NASA/TM-2005-213814, AIAA Paper 2005-3028
| Author | : Stewart A. L. Glegg |
| Publisher | : |
| Total Pages | : |
| Release | : 1993 |
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| Author | : |
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| Total Pages | : 52 |
| Release | : 1995 |
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| Author | : Cole V. Duke |
| Publisher | : |
| Total Pages | : 74 |
| Release | : 2012 |
| Genre | : Electronic dissertations |
| ISBN | : |
Active noise control (ANC) has been implemented using analog filters to reduce broadband noise from a small axial cooling fan. Previous work successfully attenuated narrow-band, tonal portions of the noise using a digital controller. The practical performance limits of this system were reached and it was desirable to attenuate the noise further. Additional research, therefore, sought to attenuate broadband noise from the fan using digital controller, but performance was limited by the group delay inherent in the digital signal processor (DSP). Current research attempts to further attenuate broadband noise and improve performance of the system by combining the tonal controller with an analog feedback controller. An analog controller is implemented in parallel with the digital controller without degrading the performance of either individual controller. Broadband noise is attenuated in a certain frequency region, but at the expense of increasing noise in adjacent frequency regions. Results show that a single-input single-output (SISO) controller is preferable to a multiple-input multiple-output (MIMO) controller for this system.
| Author | : National Aeronautics and Space Adm Nasa |
| Publisher | : Independently Published |
| Total Pages | : 98 |
| Release | : 2018-09-23 |
| Genre | : Science |
| ISBN | : 9781723944666 |
This report examines the effects on broadband noise generation of unsteady coupling between a rotor and stator in the fan stage of a turbofan engine. Whereas previous acoustic analyses treated the blade rows as isolated cascades, the present work accounts for reflection and transmission effects at both blade rows by tracking the mode and frequency scattering of pressure and vortical waves. The fan stage is modeled in rectilinear geometry to take advantage of a previously existing unsteady cascade theory for 3D perturbation waves and thereby use a realistic 3D turbulence spectrum. In the analysis, it was found that the set of participating modes divides itself naturally into "independent mode subsets" that couple only among themselves and not to the other such subsets. This principle is the basis for the analysis and considerably reduces computational effort. It also provides a simple, accurate scheme for modal averaging for further efficiency. Computed results for a coupled fan stage are compared with calculations for isolated blade rows. It is found that coupling increases downstream noise by 2 to 4 dB. Upstream noise is lower for isolated cascades and is further reduced by including coupling effects. In comparison with test data, the increase in the upstream/downstream differential indicates that broadband noise from turbulent inflow at the stator dominates downstream noise but is not a significant contributor to upstream noise.Hanson, Donald B.Glenn Research CenterTURBOFAN ENGINES; ENGINE NOISE; ROTOR STATOR INTERACTIONS; NOISE MEASUREMENT; TURBULENT FLOW; SIGNAL ANALYZERS; ACOUSTIC COUPLING; SOUND TRANSMISSION; WAVE REFLECTION; BROADBAND
| Author | : Paul R. Soderman |
| Publisher | : |
| Total Pages | : 84 |
| Release | : 1977 |
| Genre | : Fans (Machinery) |
| ISBN | : |
| Author | : |
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| Total Pages | : |
| Release | : 2004 |
| Genre | : |
| ISBN | : 9789073802827 |
