ALBERT

Description: As extensive experimental campaign was performed to study the aeroacoustic installation effects of an open rotor with respect to both a conventional tube and wing type airframe and an unconventional hybrid wing body airframe. The open rotor rig had two counter rotating rows of blades each with eight blades of a design originally flight tested in the 1980s. The aeroacoustic installation effects measured in an aeroacoustic wind tunnel included those from flow effects due to inflow distortion or wake interaction and acoustic propagation effects such as shielding and reflection. The objective of the test campaign was to quantify the installation effects for a wide range of parameters and configurations derived from the two airframe types. For the conventional airframe, the open rotor was positioned in increments in front of and then over the main wing and then in positions representative of tail mounted aircraft with a conventional tail, a T-tail and a U-tail. The interaction of the wake of the open rotor as well as acoustic scattering results in an increase of about 10 dB when the rotor is positioned in front of the main wing. When positioned over the main wing a substantial amount of noise reduction is obtained and this is also observed for tail-mounted installations with a large U-tail. For the hybrid wing body airframe, the open rotor was positioned over the airframe along the centerline as well as off-center representing a twin engine location. A primary result was the documentation of the noise reduction from shielding as a function of the location of the open rotor upstream of the trailing edge of the hybrid wing body. The effects from vertical surfaces and elevon deflection were also measured. Acoustic lining was specially designed and inserted flush with the elevon and airframe surface, the result was an additional reduction in open rotor noise propagating to the far field microphones. Even with the older blade design used, the experiment provided quantification of the aeroacoustic installation effects for a wide range of open rotor and airframe configurations and can be used with data processing methods to evaluate the aeroacoustic installation effects for open rotors with modern blade designs.

Description: Multiple compound helicopter configurations are designed using a combination of rotorcraft sizing and comprehensive analysis codes. Results from both the conceptual design phase and rotor comprehensive analysis are presented. The designs are evaluated for their suitability to a short-to-medium-haul civil transport mission carrying a payload of 90 passengers. Multiple metrics are used to determine the best configuration, with heavy emphasis placed on minimizing fuel burn.

Description: Multiple metrics are applied to the design of a large civil tiltrotor, integrating minimum cost and minimum environmental impact. The design mission is passenger transport with similar range and capacity to a regional jet. Separate aircraft designs are generated for minimum empty weight, fuel burn, and environmental impact. A metric specifically developed for the design of aircraft is employed to evaluate emissions. The designs are generated using the NDARC rotorcraft sizing code, and rotor analysis is performed with the CAMRAD II aeromechanics code. Design and mission parameters such as wing loading, disk loading, and cruise altitude are varied to minimize both cost and environmental impact metrics. This paper presents the results of these parametric sweeps as well as the final aircraft designs.

Description: This paper presents an analysis of the slat noise for Hybrid Wing Body (HWB) aircraft, based on a database from a 3% scale wind tunnel test. It is shown that the HWB slats are one of the dominant noise components, characterized by its broad spectral shape with a peak frequency that depends on both the mean flow velocity and the aircraft angle of attack, the former following the conventional Strouhal number scaling and the latter explainable by the dependence of the coherence length of the slat unsteady flows on the aircraft angle of attack. While the overall levels of the slat noise are shown to approximately follow the fifth power law in the flow Mach number, the effects of the Mach number manifest themselves in the noise spectra in both the amplitude and the spectral shape. The slat noise amplitude is shown to also depend on the angle of attack, assuming a minimum in the range of 3 to 5 degrees and increasing when the angle of attack moves away from this range. These features are all modeled and incorporated in slat noise prediction methodologies, extending the prediction capability from conventional aircraft designs to HWB configurations. Comparisons between predictions and data show very good agreements both in various parametric trends and in the absolute levels. The HWB aircraft is designed to operate at angles of attack much higher than those of conventional aircraft. This is shown to significantly increase the HWB slat noise. To further illustrate, the test data are extrapolated to full scale and compared with the slat noise of the Boeing 777 aircraft, showing that the former is higher the latter.

Description: An experimental investigation was performed to study the propulsion airframe aeroacoustic installation effects of a separate flow jet nozzle with a Hybrid Wing Body aircraft configuration where the engine is installed above the wing. Prior understanding of the jet noise shielding effectiveness was extended to a bypass ratio ten application as a function of nozzle configuration, chevron type, axial spacing, and installation effects from additional airframe components. Chevron types included fan chevrons that are uniform circumferentially around the fan nozzle and T-fan type chevrons that are asymmetrical circumferentially. In isolated testing without a pylon, uniform chevrons compared to T-fan chevrons showed slightly more low frequency reduction offset by more high frequency increase. Phased array localization shows that at this bypass ratio chevrons still move peak jet noise source locations upstream but not to nearly the extent, as a function of frequency, as for lower bypass ratio jets. For baseline nozzles without chevrons, the basic pylon effect has been greatly reduced compared to that seen for lower bypass ratio jets. Compared to Tfan chevrons without a pylon, the combination with a standard pylon results in more high frequency noise increase and an overall higher noise level. Shielded by an airframe surface 2.17 fan diameters from nozzle to airframe trailing edge, the T-fan chevron nozzle can produce reductions in jet noise of as much as 8 dB at high frequencies and upstream angles. Noise reduction from shielding decreases with decreasing frequency and with increasing angle from the jet inlet. Beyond an angle of 130 degrees there is almost no noise reduction from shielding. Increasing chevron immersion more than what is already an aggressive design is not advantageous for noise reduction. The addition of airframe control surfaces, including vertical stabilizers and elevon deflection, showed only a small overall impact. Based on the test results, the best overall nozzle configuration design was selected for application to the N2A Hybrid Wing Body concept that will be the subject of the NASA Langley 14 by 22 Foot Subsonic Tunnel high fidelity aeroacoustic characterization experiment. The best overall nozzle selected includes T-fan type chevrons, uniform chevrons on the core nozzle, and no additional pylon of the type that created a strong acoustic effect at lower bypass ratios. The T-fan chevrons are oriented azimuthally away from the ground observer locations. This best overall nozzle compared to the baseline nozzle was assessed, at equal thrust, to produce sufficient installed noise reduction of the jet noise component to enable the N2A HWB to meet NASA s noise goal of 42 dB cumulative below Stage 4.

Description: No abstract available

Description: Flight data from an entry, descent, and landing (EDL) sequence can be used to reconstruct the vehicle's trajectory, aerodynamic coefficients and the atmospheric profile experienced by the vehicle. Past Mars missions have contained instruments that do not provide direct measurement of the freestream atmospheric conditions. Thus, the uncertainties in the atmospheric reconstruction and the aerodynamic database knowledge could not be separated. The upcoming Mars Science Laboratory (MSL) will take measurements of the pressure distribution on the aeroshell forebody during entry and will allow freestream atmospheric conditions to be partially observable. This data provides a mean to separate atmospheric and aerodynamic uncertainties and is part of the MSL EDL Instrumentation (MEDLI) project. Methods to estimate the flight performance statistically using on-board measurements are demonstrated here through the use of simulated Mars data. Different statistical estimators are used to demonstrate which estimator best quantifies the uncertainties in the flight parameters. The techniques demonstrated herein are planned for application to the MSL flight dataset after the spacecraft lands on Mars in August 2012.

Description: This paper explores a comparison between experimental data and numerical simulations of the historical baseline F31/A31 open rotor geometry. The experimental data were obtained at the NASA Glenn Research Center s Aeroacoustic facility and include performance and noise information for a variety of flow speeds (matching take-off and cruise). The numerical simulations provide both performance and aeroacoustic results using the NUMECA s Fine-Turbo analysis code. A non-linear harmonic method is used to capture the rotor/rotor interaction.

Description: A conceptual design study of a large civil compound helicopter is presented. The objective is to determine how a compound helicopter performs when compared to both a conventional helicopter and a tiltrotor using a design mission that is shorter than optimal for a tiltrotor and longer than optimal for a helicopter. The designs are generated and analyzed using conceptual design software and are further evaluated with a comprehensive rotorcraft analysis code. Multiple metrics are used to determine the suitability of each design for the given mission. Plots of various trade studies and parameter sweeps as well as comprehensive analysis results are presented. The results suggest that the compound helicopter examined for this study would not be competitive with a tiltrotor or conventional helicopter, but multiple possibilities are identified for improving the performance of the compound helicopter in future research.

Description: Nozzle exit configurations and associated systems and methods are disclosed. An aircraft system in accordance with one embodiment includes a jet engine exhaust nozzle having an internal flow surface and an exit aperture, with the exit aperture having a perimeter that includes multiple projections extending in an aft direction. Aft portions of individual neighboring projections are spaced apart from each other by a gap, and a geometric feature of the multiple can change in a monotonic manner along at least a portion of the perimeter. Projections near a support pylon and/or associated heat shield can have particular configurations, including greater flow immersion than other projections.