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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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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Dynamic stall experiments on oscillating airfoils

Dynamic stall and unsteady boundary layer separation have been studied in incompressible flow at moderately large Reynolds numbers. By varying the leading-edge geometry of an NACA 0012 airfoil, three different types of stall were produced. For most of the configurations studied, including the basic NACA 0012 profile, dynamic stall was found not to originate with the bursting of a leading-edge laminar separation bubble, as is commonly believed. Instead, the vortex shedding phenomenon, which is the predominant feature of dynamic stall, appears to be fed its vorticity by the breakdown of the turbulent boundary layer.

Mccroskey, W. J.↗
NASA NTRS2016

Development of Constraint Force Equation Methodology for Application to Multi-Body Dynamics Including Launch Vehicle Stage Seperation

The objective of this report is to develop and implement a physics based method for analysis and simulation of multi-body dynamics including launch vehicle stage separation. The constraint force equation (CFE) methodology discussed in this report provides such a framework for modeling constraint forces and moments acting at joints when the vehicles are still connected. Several stand-alone test cases involving various types of joints were developed to validate the CFE methodology. The results were compared with ADAMS(Registered Trademark) and Autolev, two different industry standard benchmark codes for multi-body dynamic analysis and simulations. However, these two codes are not designed for aerospace flight trajectory simulations. After this validation exercise, the CFE algorithm was implemented in Program to Optimize Simulated Trajectories II (POST2) to provide a capability to simulate end-to-end trajectories of launch vehicles including stage separation. The POST2/CFE methodology was applied to the STS-1 Space Shuttle solid rocket booster (SRB) separation and Hyper-X Research Vehicle (HXRV) separation from the Pegasus booster as a further test and validation for its application to launch vehicle stage separation problems. Finally, to demonstrate end-to-end simulation capability, POST2/CFE was applied to the ascent, orbit insertion, and booster return of a reusable two-stage-to-orbit (TSTO) vehicle concept. With these validation exercises, POST2/CFE software can be used for performing conceptual level end-to-end simulations, including launch vehicle stage separation, for problems similar to those discussed in this report.

Pamadi, Bandu N.↗
NASA NTRS1988

Cometary H2(+) and solar wind He(2+) dynamics across the Halley cometopause

Two Mass/Charge (M/Q) of about 2 distributions were observed by the Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during the encounter with comet Halley. The first, present throughout the encounter, is identified as solar wind He(2+). The second, detectable only within about 600,000 km of the nucleus, is identified as H2(+) (produced primarily by dissociation and ionization of cometary H2O). When these two distributions are separated, distinct differences in their dynamics are apparent, particularly in the density and velocity profiles near the 'cometopause'.

Fuselier, S. A.↗
NASA NTRS1972

Abort separation of the shuttle

A sensitivity analysis of the factors which affect a successful abort maneuver following a space shuttle launching is presented. Wind tunnel tests were conducted using optimum simulation techniques and data acquisition procedures. Static stability, dynamic stability, and local loads were investigated. It is concluded that parallel abort separation of the space shuttle components is possible at both high and low dynamic pressures. Successful separation is dependent upon configuration, Mach number, rocket exhaust impingement and relative position and attitude of the stages.

Decker, J. P.↗
NASA NTRS1978

Reynolds number criticality in dynamic tests

To extrapolate from subscale wind tunnel tests to full-scale flight is a well-recognized problem. It becomes especially critical for present day high performance missiles and aircraft which operate at high angles of attack where separated flow effects often dominate the vehicle aerodynamics. The dynamic effects of flow separation can usually not be simulated at subscale Reynolds numbers. This is illustrated by examples of tests with slender vehicles and high performance aircraft. It is shown how analytic means can be developed establishing theoretical relationships between dynamic and static aerodynamic characteristics and how such means make it possible to extrapolate analytically from subscale tests to full-scale flight. The roll of future high Reynolds number facilities in establishing such 'analytic extrapolation' tools is discussed.

Ericsson, L. E.↗
NASA NTRS1989

Classes of ring galaxies generated by dynamical friction

Dynamical friction is incorporated in the numerical modeling of colliding ring galaxies. It is shown that dynamical friction may lead to the capture of an initially unbound companion into a damped oscillatory orbit before ultimately merging with the target disk. In the late stages of its motion the companion may be virtually merged with the main galaxy while rings are still propagating in the disk. This raises the possibility that there exist (at least) two classes of ring galaxies: a class of ring galaxies with separate detached companions in which dynamical friction is too weak to have captured the collider, and a second class with no apparent companion in which the latter has either merged with the target galaxy or has disrupted. These two classes could possibly be identified with O-type and P-type ring galaxies of Few and Madore (1986).

Luban-Lotan, Pnina↗
NASA NTRS2007

Proceedings of the 2004 Workshop on CFD Validation of Synthetic Jets and Turbulent Separation Control

The papers presented here are from the Langley Research Center Workshop on Computational Fluid Dynamics (CFD) Validation of Synthetic Jets and Turbulent Separation Control (nicknamed "CFDVAL2004"), held March 2004 in Williamsburg, Virginia. The goal of the workshop was to bring together an international group of CFD practitioners to assess the current capabilities of different classes of turbulent flow solution methodologies to predict flow fields induced by synthetic jets and separation control geometries. The workshop consisted of three flow-control test cases of varying complexity, and participants could contribute to any number of the cases. Along with their workshop submissions, each participant included a short write-up describing their method for computing the particular case(s). These write-ups are presented as received from the authors with no editing. Descriptions of each of the test cases and experiments are also included.

Rumsey, Christopher L.↗
NASA NTRS1978

Characterization of a swept-strut hydrogen fuel-injector for scramjet applications

Results of an experimental investigation of a swept-strut hydrogen fuel-injector simulating the center strut of a three strut scramjet module at Mach 6 flight conditions are presented. Detailed wall pressure distributions from over 100 separate tests with overall fuel flow from 0.1 to 1.3 times stoichiometric and test gas stagnation temperature from 1100 to 2400 K were recorded. The distance for pressure rise from the point of injection was found to increase with increasing test stagnation temperature. This trend indicates that chemical kinetics in the immediate region of perpendicular injection are not likely to be the mechanism controlling the onset of pressure rise. A fluid dynamic mechanism is suggested involving separation of the boundary layer downstream of injection which is forced upstream from the trailing edge by pressure rise due to combustion occurring in the base region of the strut. The results obtained indicate that the swept-strut fuel-injector concept can be adapted to a wide range of flight conditions by varying the amount of perpendicular fuel injection.

Northam, G. B.↗
NASA NTRS1990

Nonlinear inversion flight control for a supermaneuverable aircraft

This paper describes the use of nonlinear dynamic inversion for the design of a flight control system for a supermaneuverable aircraft. First, the dynamics to be controlled were separated into fast and slow variables. The fast variables were the angular rates and the slow variables were the attitude angles. Then a nonlinear inversion controller was designed for the fast variables. This stabilized the longitudinal short-period and improved the lateral-directional responses over a wide range of angle of attack by making use of a combination for aerodynamic surfaces and thrust vectoring control. Outer loops were then closed to allow the pilot to control the slow dynamics, the angle of attack, side-slip angle and the velocity bank angle. Nonlinear inversion was also used to design of the outer loop control laws. The dynamic inversion control laws were compared with more conventional, gain-scheduled control laws and were shown to yield much better performance.

Snell, S. Antony↗
NASA NTRS1985

Mechanical Mixer for Rudder/Braking Wedge

Right and left rudder panels moved separately. Mechanical mixer enables panels of two-panel rudder to rotate in same direction for steering or in opposite directions for dynamic braking. Steering and braking inputs separate so any combination of steering and braking motions executed simultaneously. Developed for aerodynamic braking of Space Shuttle orbiter, steering/braking drive train and rudder arrangement used for similar purposes on aircraft, thereby reducing sizes of thrust reversers.

Grimm, D.↗
NASA NTRS2009

Simultaneous Multiple-Location Separation Control

A method of controlling a shear layer for a fluid dynamic body introduces first periodic disturbances into the fluid medium at a first flow separation location. Simultaneously, second periodic disturbances are introduced into the fluid medium at a second flow separation location. A phase difference between the first and second periodic disturbances is adjusted to control flow separation of the shear layer as the fluid medium moves over the fluid dynamic body.

Greenblatt, David↗
NASA NTRS1995

Merger of a Neutron Star with a Newtonian Black Hole

Newtonian smooth particle hydro simulations are presented of the merger of a 1.4 solar mass neutron star with a black hole of equal mass. The initial state of the system is modeled with a stiff polytrope orbiting a point mass. Dynamical instability sets in when the orbital separation is equal to about three stellar radii. The ensuing mass transfer occurs on the dynamical timescale. No accretion torus is formed. At the end of the computation a corona of large extent shrouds an apparently stable binary system of a 0.25 solar mass star orbiting a 2.3 solar mass black hole.

Lee, William H.↗
NASA NTRS2018

Impact of August 2017 British Columbia Pyrocumulonimbus Injection Events on Lower Stratospheric Composition

On August 12-13, 2017 large wildfires in the Cariboo region of British Columbia, Canada sparked a series of pyrocumulonimbus events lifting carbonaceous aerosol and other trace gases to the tropopause region (~10-11 km). Over the subsequent days, this plume of trace gas and aerosol species was observed from numerous NASA satellite instruments to rise to over 22 km due to the strong shortwave heating of the carbonaceous aerosol. We will show observations of CO and H2O from the Microwave Limb Sounder (MLS) instrument on Aura satellite demonstrating the clear rise and spread of the plume which can be coherently tracked for at least 2 months. Enhancements in HCN, CH3CN, and methanol (CH3OH) are also evident in MLS measurements with the former two having low vertical resolution. We have also detected a significantly lower concentration of O3 and HNO3 in the plume compared to the surrounding environment, which is consistent with a dynamical perturbation from the rapid diabatic rise of the heated plume from the tropopause through the lower stratosphere. In the weeks and months that followed this plume spread over much of the Northern Hemisphere and the aerosol was observed to be slowly removed by transport back into the troposphere. We will compare and contrast the Aug. 2017 event with the other large event in the MLS record, the Feb. 2009 Australian "Black Saturday" event, and use the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) replayed to observed meteorology to understand the effect of the British Columbia event on trace gas species. GEOSCCM helps us to separate the relative roles of dynamics and chemistry on lower stratospheric trace gas composition changes, not only in the rising plume but also the impact of its eventual spread over the Northern Hemisphere during fall and winter of 2017-2018.

Oman, Luke D.↗
NASA NTRS1983

Dynamic Distortion in a Short S-Shaped Subsonic Diffuser with Flow Separation

An experimental investigation of the time varying distortion at the diffuser exit of a subscale HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels is also presented.

Stumpf, R.↗
NASA NTRS1983

Dynamic distortion in a short s-shaped subsonic diffuser with flow separation

An experimental investigation of the time varying distortion at the diffuser exit of a subsonic HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels are also presented. Previously announced in STAR as N83-26838

Stumpf, R.↗
NASA NTRS2019

Flow-Field Measurements in a Wing-Fuselage Junction Using an Embedded Particle Image Velocimetry System

A novel, embedded, 2D Particle Image Velocimetry system has been developed and implemented to obtain off-body velocity measurements in the junction of an 8% wing-body configuration in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Although the initial purpose for implementing the system during this test was to evaluate system performance and identify potential risks, the system worked remarkably well and a considerable amount of data were obtained in the wing-fuselage junction near the trailing edge at a Reynolds Number of 2.4 Million and angle of attack of 5 degrees. In addition to providing notable efficiencies with regard to image acquisition and test operations, the PIV system proved to be quite capable of capturing unique details of the flow separation to complement the extensive suite of measurement techniques applied during the test. Instantaneous PIV vector fields reveal that the flow separation is not stationary but rather highly dynamic. Mean flow statistics calculated from the PIV measurements highlight where reverse flow and Reynolds stresses are concentrated in the separated region and agree well with results from the embedded Laser Doppler Velocimeter system and Computational Fluid Dynamics. The comparisons and additional insight gained during this effort will help guide system improvements for follow-on tests.

Jenkins, Luther N.↗
NASA NTRS2019

Update on the Juncture Flow PIV Results and Future Plans

A novel, embedded, 2D Particle Image Velocimetry system has been developed and implemented to obtain off-body velocity measurements in the junction of an 8% wing-body configuration in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Although the initial purpose for implementing the system during this test was to evaluate system performance and identify potential risks, a considerable amount of data were obtained in the wing-fuselage junction near the trailing edge at a Reynolds Number of 2.4 Million and angle of attack of 5 degrees. In addition to providing notable efficiencies with regard to image acquisition and test operations, the PIV system captured unique details of the flow separation to complement the extensive suite of measurement techniques applied during the test. Instantaneous PIV vector fields reveal that the flow separation is not stationary but rather highly dynamic. Mean flow statistics calculated from the PIV measurements highlight where reverse flow and Reynolds stresses are concentrated in the separated region and agree well with results from the embedded Laser Doppler Velocimeter system and Computational Fluid Dynamics. The comparisons and ional insight gained during this effort will help guide system improvements for the upcoming entry in 2020.

Jenkins, Luther N.↗
NASA NTRS2001

Nanoklystron: A Monolithic Tube Approach to THz Power Generation

The authors propose a new approach to THz power generation: the nanoklystron. Utilizing silicon micromachining techniques, the design and fabrication concept of a monolithic THz vacuum-tube reflex-klystron source is described. The nanoklystron employs a separately fabricated cathode structure composed of densely packed carbon nanotube field emitters and an add-in repeller. The nanotube cathode is expected to increase the current density, extend the cathode life and decrease the required oscillation voltage to values below 100 V. The excitation cavity is based on ridged-waveguide and differs from the conventional cylindrical re-entrant structures found in lower frequency klystrons. A quasi-static field analysis of the cavity and output coupling structure show excellent control of the quality factor and desired field distribution. Output power is expected to occur through an iris coupled matched rectangular waveguide and integrated pyramidal feed horn. The entire circuit is designed so as to be formed monolithically from two thermocompression bonded silicon wafers processed using deep reactive ion etching (DRIE) techniques. To expedite prototyping, a 600 GHz mechanically machined structure has been designed and is in fabrication. A complete numeric analysis of the nanoklystron circuit, including the electron beam dynamics has just gotten underway. Separate evaluation of the nanotube cathodes is also ongoing. The authors will describe the progress to date as well as plans for the immediate implementation and testing of nanoklystron prototypes at 640 and 1250 GHz.

Siegel, Peter H.↗