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Results for “FORCED OSCILLATION”

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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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Numerical simulation of self-sustained and forced oscillations in jet shear layers

Excitation of axisymmetric jet shear layers has been investigated by solving the time-dependent compressible Navier-Stokes equations. MacCormack's explicit finite difference scheme is used in performing the computations on a CRAY X-MP computer. This work examines the influence of various means of excitation of the shear layer, to produce large scale vortex structures in such a manner that the mixing between two flows will be enhanced or diminished. While successful pressure excitation has been achieved in previous studies only limited success with temperature excitation at the inflow boundary has been accomplished. The current study focuses on the use of temperature excitation through the boundary layer immediately inside the jet lip. In order to achieve the required resolution significant grid refinement is necessary. The results of the computation with and without temperature excitation are analyzed and compared with results obtained using pressure excitation. The influence of amplitude and frequency on specific flow characteristics are also examined. The excitation frequency for both the temperature and pressure corresponds to a Strouhal number of .45 and the inflow jet Mach number is approximately .3.

Scott, J. N.↗
NASA NTRS2014

Hybrid Wing Body Model Identification Using Forced-Oscillation Water Tunnel Data

Static and dynamic testing of the NASA 0.7 percent scale Hybrid Wing Body (HWB) configuration was conducted in the Rolling Hills Research Corporation water tunnel to investigate aerodynamic behavior over a large range of angle-of-attack and to develop models that can predict aircraft response in nonlinear unsteady flight regimes. This paper reports primarily on the longitudinal axis results. Flow visualization tests were also performed. These tests provide additional static data and new dynamic data that complement tests conducted at NASA Langley 14- by 22-Foot Subsonic Tunnel. HWB was developed to support the NASA Environmentally Responsible Aviation Project goals of lower noise, emissions, and fuel burn. This study also supports the NASA Aviation Safety Program efforts to model and control advanced transport configurations in loss-of-control conditions.

Murphy, Patrick C.↗
NASA NTRS1984

Wind-tunnel free-flight investigation of a model of a forward-swept-wing fighter configuration

A wind-tunnel free-flight investigation was conducted to study the dynamic stability characteristics of a model of a forward-swept-wing fighter-airplane configuration at high angles of attack. Various other wind-tunnel techniques employed in the study included static- and dynamic- (forced-oscillation) force tests, free-to-roll tests, and flow-visualization tests. A unique facet of the study was the extreme level of static pitch instability (in excess of negative 32-percent static margin) inherent in the airframe design which precluded free-flight testing without stability augmentation in pitch. Results are presented which emphasize the high-angle-of-attack aerodynamics and the vehicle-component contributions to these characteristics. The effects of these aerodynamic characteristics on the high-angle-of-attack flying qualities of the configuration are discussed in terms of results of the wind-tunnel free-flight tests.

Murri, D. G.↗
DOE OSTI2020

Pacific decadal oscillation remotely forced by the equatorial Pacific and the Atlantic Oceans

Abstract The Pacific Decadal Oscillation (PDO), the leading mode of Pacific decadal sea surface temperature variability, arises mainly from combinations of regional air-sea interaction within the North Pacific Ocean and remote forcing, such as from the tropical Pacific and the Atlantic. Because of such a combination of mechanisms, a question remains as to how much PDO variability originates from these regions. To better understand PDO variability, the equatorial Pacific and the Atlantic impacts on the PDO are examined using several 3-dimensional partial ocean data assimilation experiments conducted with two global climate models: the CESM1.0 and MIROC3.2m. In these partial assimilation experiments, the climate models are constrained by observed temperature and salinity anomalies, one solely in the Atlantic basin and the other solely in the equatorial Pacific basin, but are allowed to evolve freely in other regions. These experiments demonstrate that, in addition to the tropical Pacific’s role in driving PDO variability, the Atlantic can affect PDO variability by modulating the tropical Pacific climate through two proposed processes. One is the equatorial pathway, in which tropical Atlantic sea surface temperature (SST) variability causes an El Niño-like SST response in the equatorial Pacific through the reorganization of the global Walker circulation. The other is the north tropical pathway, where low-frequency SST variability associated with the Atlantic Multidecadal Oscillation induces a Matsuno-Gill type atmospheric response in the tropical Atlantic-Pacific sectors north of the equator. These results provide a quantitative assessment suggesting that 12–29% of PDO variance originates from the Atlantic Ocean and 40–44% from the tropical Pacific. The remaining 27–48% of the variance is inferred to arise from other processes such as regional ocean-atmosphere interactions in the North Pacific and possibly teleconnections from the Indian Ocean.

Meteorology & Atmospheric Sciences↗
NASA NTRSDate not supplied

A Study on Effect of Tuning Capacitor in Dynamic Radioisotope Power Systems

This study presents the effect of tuning capacitors on the power factor and power output of a gas spring-based free-piston Stirling convertor—Advanced Stirling convertor—when the convertor runs on a forced-oscillation type controller. More specifically, this paper studies how off-nominal tuning capacitance values affects the Stirling convertor in terms of the piston stability and electrical power output, when the convertor is operated by forced-oscillation type controller, such as an alternating current bus controller, and operating conditions of the convertor are unchanged. It has been widely known that tuning capacitors are important circuit components to stabilize the piston amplitude of the free-piston Stirling convertors and correct the power factor for high electrical power output. Recent modeling analysis conducted by NASA Glenn Research Center, however, suggests that while the stability of the convertor is affected by the tuning capacitor value, the power factor and the electrical power output are not affected by the tuning capacitor value, as long as the convertor is controlled by a forced-oscillation controller and the convertor operating conditions, such as the hot-end/cold-end temperatures, piston amplitude, and operating frequency, are unchanged. To verify the modeling analysis results, a test setup is devised where the convertor is controlled by a forced-oscillation controller and the piston amplitude, hot-end temperature, and charge pressure are controlled to 4mm, 760˚C, and 485psig, respectively, while the tuning capacitor value is changed from its nominal value, 840μF to 1040μF and 1240μF. Furthermore, the vibration test results of the same convertor with the three tuning capacitor values are also presented in this paper to show the effect of the tuning capacitor value on the convertor stability. The test results suggest that when the convertor is controlled by a forced-oscillation, the tuning capacitor value determines the convertor stability but not the power factor nor electrical power output. Therefore, the tuning capacitance value in forced-oscillation controllers should be determined based on the convertor stability, system mass, and volume.

Free-Piston Stirling Convertor Controller↗