Nathan Burnside

MICROPHONE ARRAY ASSESSMENT OF AN ISOLATED, 26%-SCALE, HIGH-FIDELITY LANDING GEAR

An aeroacoustic study of a 26%-scale landing gear model was conducted in the NASA Ames 7- by 10-Foot Wind Tunnel using a phased microphone array. The incorporation of complex parts via stereo lithography produced a model that can mimic full-scale details down to 3 mm. These details include the contours, brake cylinders, bolt holes, and wheel hubs that appear on the real landing gear. Major noise sources were identified and ranked. From the sideline view, the noise levels of the cable harness and torque link were each at least 8 dB above that of a clean configuration. Sources from the more ambiguous fly-over view, such as the front axle, center axle and rear axle regions, were 11 dB above the clean configuration for frequencies below 2000 Hz full-scale. This increment in noise likely included other sources situated behind the truck. Referenced to the clean configuration, the braces and links contributed as much as 8 dB. Tests with a fully sealed fairing on the landing gear suggest, through careful design of major components, a noise reduction of up to 15 dB can be achieved although 2 to 6 dB of noise reduction is probably a more realistic goal. NOMENCLATURE

High-Speed Jet Noise Reduction Using Microjets on a Jet Engine

by a jet engine. Experiments were conducted at the NASA Ames Research Center using a General Electric YJ97-GE-3 turbofan jet engine that was equipped with a 317.5 mm converging nozzle. The engine was operated at conditions that resulted in jets with fully expanded Mach numbers of 0.9 and 1.3. The microjets were generated using up to 48 evenly spaced micro-nozzles that had exit diameters of 1.2 and 2.4 mm. The operating pressure of the microjets was varied from 7.9 to 42.4 bar. Various microjet configurations were used resulting in a total mass flux of the microjets that ranged from 0.5 to 2.3 % of the primary mass flux for the subsonic jet and from 0.3 to 1.0 % of the primary mass flux for the supersonic jet. Through the various configurations it was found that reductions of up to 2 dB in the OASPL could be obtained for both the subsonic and supersonic jets. The reductions for the subsonic jet were seen at all frequencies while they were seen primarily at the higher frequencies for the supersonic jet. A reduction of about 2 dB in the shock noise of the supersonic jet was also observed.

Airframe noise study of a Bombardier CRJ-700 aircraft model in the NASA Ames 7- by 10-foot wind tunnel

An acoustic and aerodynamic experimental study was conducted of a 7%-scale unpowered Bombardier CRJ-700 aircraft model in the NASA Ames 7- by 10-Foot Wind Tunnel for the purpose of identifying and attenuating airframe noise sources. Simulated landing, takeoff and approach configurations were evaluated at Mach 0.22 and 0.26. With a phased-microphone array mounted in the ceiling over the inverted model, various noise sources in the high-lift system, landing gear, fins, and other miscellaneous components were located and compared for sound level and frequency at one flyover location. Numerous model modifications and noise-alleviation devices were evaluated. Simultaneous with acoustic measurements, aerodynamic forces were recorded to document aircraft conditions and any performance changes caused by the geometric modifications. Such performance changes were small and are not reported here. Ten airframe noise sources were identified that might be important to approach and landing noise of the full-scale aircraft The top five noise sources were: a) slat gap, b) main gear, c) flap tips at wing crank, d) flap inboard gap, and e) slat inboard tip. Relative strengths of these sources were documented along with their dependence on aircraft configuration and operating condition. Although the data were scaled to full-scale frequencies, no extrapolation to full-scale flyover was attempted.

AMELIA CESTOL Test: Acoustic Characteristics of Circulation Control Wing with Leading-and Trailing-Edge Slot Blowing

The AMELIA Cruise-Efficient Short Take-off and Landing (CESTOL) configuration concept was developed to meet future requirements of reduced field length, noise, and fuel burn by researchers at Cal Poly, San Luis Obispo and Georgia Tech Research Institute under sponsorship by the NASA Fundamental Aeronautics Program (FAP), Subsonic Fixed Wing Project. The novel configuration includes leading- and trailing-edge circulation control wing (CCW), over-wing podded turbine propulsion simulation (TPS). Extensive aerodynamic measurements of forces, surfaces pressures, and wing surface skin friction measurements were recently measured over a wide range of test conditions in the Arnold Engineering Development Center(AEDC) National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Ft Wind Tunnel. Acoustic measurements of the model were also acquired for each configuration with 7 fixed microphones on a line under the left wing, and with a 48-element, 40-inch diameter phased microphone array under the right wing. This presentation will discuss acoustic characteristics of the CCW system for a variety of tunnel speeds (0 to 120 kts), model configurations (leading edge(LE) and/or trailing-edge(TE) slot blowing, and orientations (incidence and yaw) based on acoustic measurements acquired concurrently with the aerodynamic measurements. The flow coefficient, Cmu= mVSLOT/qSW varied from 0 to 0.88 at 40 kts, and from 0 to 0.15 at 120 kts. Here m is the slot mass flow rate, VSLOT is the slot exit velocity, q is dynamic pressure, and SW is wing surface area. Directivities at selected 1/3 octave bands will be compared with comparable measurements of a 2-D wing at GTRI, as will as microphone array near-field measurements of the right wing at maximum flow rate. The presentation will include discussion of acoustic sensor calibrations as well as characterization of the wind tunnel background noise environment.

Phased acoustic array measurements of a 5.75% hybrid wing body aircraft

Detailed acoustic measurements of the noise from the leading-edge Krueger flap of a 5.75% hybrid wing body aircraft model were acquired with a traversing phased microphone array in the Arnold Engineering Development Complex NFAC 40- by 80-foot wind tunnel. The spatial resolution of the array was sufficient to distinguish between individual support brackets over the full-scale frequency range of 100 to 2875 Hz. For conditions representative of landing and take-off configuration, the noise from the brackets dominated other sources near the leading edge. Inclusion of flight-like brackets for select conditions highlights the importance of including the correct number of leading-edge high-lift device brackets with sufficient scale and fidelity. These measurements support the development of a Krueger noise model which includes cove and bracket noise.

Phased Acoustic Array Measurements of a 5.75% Hybrid Wing body Aircraft (Invited)

Detailed acoustic measurements of the noise from the leading-edge Krueger flap of a 5.75% Hybrid Wing Body (HWB) aircraft model were recently acquired with a traversing phased microphone array in the AEDC NFAC 40by 80-Foot Wind Tunnel at NASA Ames Research Center. The spatial resolution of the array was sufficient to distinguish between individual support brackets over the full-scale frequency range of 100 to 2875 Hz. For conditions representative of landing and take-off configuration, the noise from the brackets dominated other sources near the leading edge. Inclusion of flight-like brackets for select conditions highlights the importance of including the correct number of leading-edge highlift device brackets with sufficient scale and fidelity. These measurements will support the development of new predictive models.

Heated Helium to Simulate Surface Pressure Fluctuations Created by Rocket Motor Plumes

The solid-rocket plumes from the abort motor of the multipurpose crew vehicle were simulated using hot, high-pressure, helium gas to determine pressure fluctuations on the vehicle surface in the event of an abort. About 80 different abort situations over a Mach number range of 0.3 to 1.2, and vehicle attitudes of ±14  deg, were simulated using a 6% scaled model inside the NASA Ames Transonic Wind Tunnel. The test showed very high level of surface pressure fluctuations caused by the hydrodynamic near-field of the plume shear layer. The plumes grew in size with increasing flight Mach number, which was associated with a lowering of the ambient pressure. This caused an increase of plume impingement on the vehicle. Interestingly, the trend was a decrease in the level of pressure fluctuations with increasing impingement. The wind-tunnel data were compared against flight data from the Pad Abort 1 flight test. Despite various differences between the transient-flight situation and the steady-state wind-tunnel simu...

Acoustic Surveys of a Scaled-Model CESTOL Transport Aircraft in Static and Forward Speed Conditions

An 11% scale-model of a Cruise-Efficient Short Take-off and Landing (CESTOL) scalemodel test was recently completed. The test was conducted in the AEDC National Full-Scale Aerodynamic Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames Research Center. The model included two over-wing pod-mounted turbine propulsion simulators (TPS). The hybrid blended wing-body used a circulation control wing (CCW) with leadingand trailing-edge blowing. The bulk of the test matrix included three forward velocities (40 kts, 60 kts, and 100kts), angle-of-attack variation between -5o and 25o, and CCW mass flow variation. Seven strut-mounted microphones outboard of the left wing provided source directivity. A phased microphone array was mounted outboard of the right wing for source location. The goal of this paper is to provide a preliminary look at the acoustic data acquired during the Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA) test for 0o angle-of-attack and 0o sideslip conditions. Data presented provides a good overview of the test conditions and the signal-to-noise quality of the data. TPS height variation showed a difference of 2 dB to 3 dB due to wing shielding. Variation of slot mass flow showed increases of 12 dB to 26 dB above the airframe noise and the TPS increased the overall levels an additional 5 dB to 10 dB.

Measurement of Approach Noise Footprints of a C-17 STOL Aircraft During Conventional and Noise-Mitigating Approach Trajectories

Several conventional and noise-mitigating landing approach patterns were recently successfully demonstrated with a C-17 STOL aircraft, as part of an ongoing study of the integration of ESTOL-class aircraft into the national airspace system. During the demonstration, ground measurements of approach noise were obtained with an array of ground measurement stations at the NASA Dryden Research Flight Center. The measurements confirm projected trends of reduced noise impact to the greater airport vicinity for noise-mitigating approaches relative to a conventional 3 ̊ glide-slope approach.

Measurements of unsteady pressure fluctuations in the near-field of a solid rocket motor plume

Near-plume fluctuating pressures were measured during five static burns of a two-stage solid rocket motor. An array of 11 water-cooled dynamic pressure sensors was used for the near-field survey, and a condenser microphone was used to monitor the far-field acoustic fluctuations. During the initial high-thrust phase of the burn, the plume was nearly ideally expanded, while in the following low-thrust phase, it was highly over-expanded and showed the presence of clear shock patterns. This paper presents time histories and spectra measured for the two thrust conditions. Spectra from very close to the plume show high levels of low-frequency fluctuations which are known to produce significant vibro-acoustic response of the spacecraft structures. The far-field microphone signal was dominated by mixing noise with little evidence of contribution from shock-associated noise, even for the over-expanded condition. The work was performed in support of an effort to improve predictions of the acoustic environment of a manned spacecraft, such as NASAs Orion Crew Vehicle, during pad abort scenarios.