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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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This talk details the planning and outlook for the results of the 2020 ecoDemonstrator flight test.
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The sixth order Combined Compact Differencing (CCD) scheme of Chu and Fan is optimized, resulting in exceptional performance. Results indicate that the best of these optimized schemes can accurately propagate linear simple harmonic waves with fewer than three points per wavelength, while using a three point differencing stencil. Stable and accurate boundary treatments for these schemes are given, and the performance of these schemes is assessed using a benchmark problem.
This presentation documents the progress made and challenges remaining in the development of NASA's 4D space-time mapping CAA code.
This presentation documents the progress made and challenges remaining in the development of NASA's 4D space-time mapping CAA code.
Computational results are presented for an 8%-scale, full-span, transonic truss-braced wing (TTBW) model simulated as installed in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel and in free-air conditions. The simulations were conducted with the lat-tice Boltzmann solver PowerFLOW® to capture the time-accurate characteristics of the flow. The aerodynamic behavior of the aircraft was investigated in the landing configuration, with high-lift devices and landing gear deployed, as well as in the clean (cruise) configuration, with these components stowed. Analyses were performed on local flow quantities, global forces, and time-averaged surface pressures. Aerodynamic quantities were shown to be sensitive to mesh resolution levels, driven by small geometric features inherent to the TTBW model. Flow features of the TTBW model were examined, with the wing/strut configuration of this model presenting unique behaviors generally not found in conventional transport aircraft. Near-field, time-dependent flow quantities obtained from the scale-resolving simulations were used in conjunction with a Ffowcs-Williams and Hawkings integral approach to predict the far-field airframe noise signature of this advanced concept. The effects of permeable data sur-face end caps on the far-field noise spectrum in the flyover direction were determined to be negligible.
High-fidelity, time-dependent simulations of a Boeing-designed, transonic, truss-braced-wing aircraft in cruise (clean) and landing configurations are leveraged to generate synthetic microphone-phased-array data for airframe noise prediction and assessment. These data sets are used to compute source localization (beamform) maps to determine the location and strength of primary and secondary airframe noise sources associated with this unique configuration. The synthetic phased-array implementation mimics the setup of a flight test. As this study is ongoing, preliminary integrated far-field spectra for the cruise configuration obtained at multiple spatial resolutions revealed significant tonal content that lacked convergence with increased resolution. The origin of several of these tones and their unusual convergence behavior was traced to the larger-than-normal trailing-edge thickness of the “as-tested” cruise model being simulated. Reducing the trailing-edge thickness to more realistic values eliminated most of the tones at low to moderate frequencies and improved spectrum convergence significantly. Applying lessons learned from the cruise simulations, several modifications to the geometry of the landing configuration were made and are described in this work. Results from permeable and solid Ffowcs-Williams and Hawkings surfaces at two different spatial resolutions (coarse and medium) are used to illustrate the major noise sources and determine convergence of the CLEAN integrated noise levels for the entire aircraft as well as major subcomponents. We demonstrate that the low-frequency content of the far-field spectrum is dominated by noise generated from the main landing gear, while the medium- and high-frequency content is dominated by the wing-leading-edge Krueger flaps. Since analysis of the acoustic maps for the landing configuration revealed several clusters of multiple sources along the wing leading edge, “high resolution” processing of the array data was used to distinguish more accurately the locations of sources.
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Space vehicle structural vibration induced by acoustic and aerodynamic noise
The problem of in-flight aerodynamic noise has been studied by reliable estimates of full scale surface-pressure fluctuations from scale model tests in wind tunnels. Scaling relationships have been verified, and many details of the fluctuating pressure characteristics such as spatial correlation and convection velocities are understood. The effects of the wind tunnel environmental turbulence and noise have also been investigated sufficiently so that threshold levels of usable data are known.
This work which is intended to shed more light on the acoustic and fluid dynamic characteristics of jet flap type exhaust flows, reports and discusses some typical experimental results obtained with cold model air jets in a reverberation chamber. Acoustic data on the total sound power output and the overall noise spectrum of various jet flap configurations are given and compared with data from conventional circular jets. In addition various flow data for the same jets resulting from hot wire measurements are reported and general conclusions are obtained regarding the expected noise source distribution. The results indicate the dependence of the acoustic and flow characteristics on the major nozzle parameters. For the jet flaps the total radiated sound power is found to follow a 3 to 6 power of the exhaust velocity while for the circular jets the 8 power law is confirmed. The noise produced in the secondary mixing region downstream of the flap trailing edge tends to exceed the noise issuing from the primary mixing region.