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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 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Wake vortex detection at Denver Stapleton Airport with a pulsed 2-micron coherent lidar

This report describes the effort undertaken to relate aircraft wake history to the local environment. This involved the monitoring of the embedded windfield, monitoring of local meteorological parameters, a high-resolution velocity field analysis in vertical scan planes and measurement of the axial velocity signature. A flashlight pumped 2.09 micron solid state coherent laser radar system was used to detect and track wake vortices. Strong wake vortex signatures were measured for moderate to large aircraft at Denver's Stapleton airport and a large vortex database was compiled.

Hannon, Stephen M.↗
NASA NTRS1994

Integration of a mechanical forebody vortex control system into the F-15

The goal of the F-15 Forebody Vortex Control (FVC) program is to develop a production FVC system for the F-15. The system may consist of either a mechanically actuated device such as the strakes developed for the HARV program, or a pneumatic device such as the port blowing system being tested on the X-29. Both types of systems are being evaluated under this program. Background information on the F-15 and a description and overview of forebody vortex controls (FVC) will be presented.

Boalbey, Richard E.↗
NASA NTRS1994

Plasma arc welding torch having means for vortexing plasma gas exiting the welding torch

A plasma arc welding torch is described wherein a plasma gas is directed through the body of the welding torch and out of the body across the tip of the welding electrode disposed at the forward end of the body. The plasma gas is provided with a vortexing motion prior to exiting the body by a vortex motion imparting member which is mounted in an orifice housing member and carried in the forward portion of the torch body. The orifice housing member is provided with an orifice of an predetermined diameter through which the electric arc and the plasma gas exits.

Rybicki, Daniel J.↗
NASA NTRS1994

Fundamental mechanisms in premixed flame propagation via vortex-flame interactions: Numerical simulations

The goal of the present study is to assess numerically the ability of single-step and two-step chemical models to describe the main features encountered during the interaction between a two-dimensional vortex pair and a premixed laminar flame. In the two-step mechanism, the reaction kinetics are represented by a first chain branching reaction A + X yields 2X and a second chain termination reaction X + X yields P. This paper presents the fundamental mechanisms occurring during vortex-flame interactions and the relative impact of the major parameters encountered in turbulent premixed flames and suspected of playing a role in quenching mechanism: (1) Influence of stretch is investigated by analyzing the contribution of curvature and tangential strain on the local structure of the flame. The effect of Lewis number on the flame response to a strained field is analyzed. (2) Radiative heat losses which are suspected to be partially or totally responsible for quenching are also investigated. (3) The effect of the diffusion of the radicals is studied using a two-step mechanism in which an intermediate species is present. The parameters of the two-step mechanism are entirely determined from physical arguments. (4) Precise quantitative comparisons between the DNS and the experimental results of Samaniego et al are performed. These comparisons concern the evolution of the minimum heat release rate found along the flame front during the interaction and the distribution of the heat release rate along the flame front.

Mantel, Thierry↗
NASA NTRS1994

Direct numerical simulations of on-demand vortex generators: Mathematical formulation

The objective of the present research is the development and application of efficient adaptive numerical algorithms for the study, via direct numerical simulations, of active vortex generators. We are using innovative computational schemes to investigate flows past complex configurations undergoing arbitrary motions. Some of the questions we try to answer are: Can and how may we control the dynamics of the wake? What is the importance of body shape and motion in the active control of the flow? What is the effect of three-dimensionality in laboratory experiments? We are interested not only in coupling our results to ongoing, related experimental work, but furthermore to develop an extensive database relating the above mechanisms to the vortical wake structures with the long-range objective of developing feedback control mechanisms. This technology is very important to aircraft, ship, automotive, and other industries that require predictive capability for fluid mechanical problems. The results would have an impact in high angle of attack aerodynamics and help design ways to improve the efficiency of ships and submarines (maneuverability, vortex induced vibration, and noise).

Koumoutsakos, Petros↗
NASA NTRS1994

A wind tunnel investigation of the effects of micro-vortex generators and Gurney flaps on the high-lift characteristics of a business jet wing

A study of a full-scale, semi-span business jet wing has been conducted to investigate the potential of two types of high-lift devices for improving aircraft high-lift performance. The research effort involved low-speed wind-tunnel tests of micro-vortex generators and Gurney flaps applied to the flap system of the business jet wing and included force and moment measurements, surface pressure surveys and flow visualization on the wing and flap. Results showed that the micro-vortex generators tested had no beneficial effects on the longitudinal force characteristics in this particular application, while the Gurney flaps were an effective means of increasing lift. However, the Gurney flaps also caused an increase in drag in most circumstances.

Martuccio, Michelle Therese↗
NASA NTRS1994

Spring dehydration in the Antarctic stratospheric vortex observed by HALOE

The distribution of dehydrated air in the middle and lower stratosphere during the 1992 Southern Hemisphere spring is investigated using Halogen Occultation Experiment (HALOE) observations and trajectory techniques. Comparisons between previously published Version 9 and the improved Version 16 retrievals on the 700-K isentropic surface show very slight (0.05 ppmv) increases in Version 16 CH4 relative to Version 9 within the polar vortex. Version 16 H2O mixing ratios show a reduction of 0.5 ppmv relative to Version 9 within the polar night jet and a reduction of nearly 1.0 ppmv in middle latitudes when compared to Version 9. The version 16 HALOE retrievals show low mixing ratios of total hydrogen (2CH4 + H2O) within the polar vortex on both 700 and 425 K isentropic surfaces relative to typical middle-stratospheric 2CH4 + H2O mixing ratios. The low 2CH4 + H2O mixing ratios are associated with dehydration. Slight reductions in total hydrogen, relative to typical middle-stratospheric values, are found at these levels throughout the Southern Hemisphere during this period. Trajectory calculations show that middle-latitude air masses are composed of a mixture of air from within the polar night jet and air from middle latitudes. A strong kinematic barrier to large-scale exchange is found on the poleward flank of the polar night jet at 700 K. A much weaker kinematic barrier is found at 425 K. The impact of the finite tangent pathlength of the HALOE measurements is investigated using an idealized tracer distribution. This experiment suggests that HALOE should be able to resolve the kinematic barrier, if it exists.

Pierce, R. Bradley↗
NASA NTRS1994

Chemical change in the arctic vortex during AASE 2

We measured column abundances of HF, HCl, O3, HNO3, and H2O on the NASA DC-8 during the AASE II campaign, using thermal emission spectroscopy. We made multiple traversals of the Arctic vortex and surroundings. Using HF as a tracer, we remove the effects of subsidence from the measured column abundances; perturbations in the resulting column abundances are attributed to chemical processing. We find that by January 1992 the stratospheric column in the vortex had been chemically depleted by about (55+/-10)% in HCl and (35+/-10)% in O3, and enhanced by about (15+/-10)% in HNO3 and (0+/-10)% in H2O.

Traub, Wesley A.↗
NASA NTRS1993

MLS CLO observations and arctic polar vortex temperatures

Analysis of Upper Altmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) observations in early January 1992 shows a clear relationship between predicted polar stratospheric cloud formation along the back trajectory and elevated ClO amounts. These findings are in good agreement with aircraft observations. The MLS observed variation of ClO amounts within the vortex also fits the pattern of ClO change as a result of air parcel solar exposure and nitric acid photolysis. Outside the polar vortex, the occasional highly elevated ClO appear statistically consistent with MLS measurement noise.

Schoeberl, M. R.↗
NASA NTRS1993

Use of stratospheric aerosol properties as diagnostics of Antarctic vortex processes

Physical properties of the stratospheric aerosol population are inferred from cloud-free SAGE II multiwavelength extinction measurements in the Antarctic during late summer (February/March) and spring (September/October, November). Seasonal changes in these properties are used to infer physical processes occurring in the Antarctic stratosphere over the course of the winter. The analysis suggests that the apparent springtime cleansing of the Antarctic stratosphere is the result of aerosol redistribution through subsidence of the polar vortex air mass and sedimentation of large polar stratospheric cloud particles. The analysis also suggests that vortex processes are responsible for a significant downward transport of aerosol through the tropopause.

Thomason, Larry W.↗
NASA NTRS1994

Reduction of blade-vortex interaction noise through porous leading edge

The effect of the porous leading edge of an airfoil on the blade-vortex interaction noise, which dominates the far-field acoustic spectrum of the helicopter, is investigated. The thin-layer Navier-Stokes equations are solved with a high-order upwind-biased scheme and a multizonal grid system. The Baldwin-Lomax turbulence model is modified for considering transpiration on the surface. The amplitudes of the propagating acoustic wave in the near field are calculated directly from the computation. The porosity effect on the surface is modeled in two ways: (1) imposition of prescribed transpiration velocity distribution and (2) calculation of transpiration velocity distribution by Darcy's law. Results show leading-edge transpiration can suppress pressure fluctuations at the leading edge during blade-vortex interaction and consequently reduce the amplitude of propagating noise by 30% at a maximum in the near field.

Lee, Soogab↗
NASA NTRS1995

Prediction and measurement of blade-vortex interaction loading

An extensive quantity of airload measurements was obtained for a pressure-instrumented model of the BO-105 main rotor for a large number of higher-harmonic control (HHC) settings at Duits-Nederlandse Wind Tunnel (DNW). The wake geometry, vortex strength, and vortex core size were also measured through a laser light sheet technique and LDV. These results are used to verify the BVI airload prediction methodologies developed by AFDD, DLR, NASA Langley, and ONERA. The comparisons show that an accurate prediction of the blade motion and the wake geometry is the most important aspect of the BVI airload predictions.

Tung, Chee↗
NASA NTRS1995

Vortex perturbation dynamics

An initial value approach is used to examine the dynamics of perturbations introduced into a vortex under strain. Both the basic vortex considered and the perturbations are taken as fully three-dimensional. An explicit solution for the time evolution of the vorticity perturbations is given for arbitrary initial vorticity. Analytical solutions for the resulting velocity components are found when the initial vorticity is assumed to be localized. For more general initial vorticity distributions, the velocity components are determined numerically. It is found that the variation in the radial direction of the initial vorticity disturbance is the most important factor influencing the qualitative behavior of the solutions. Transient growth in the magnitude of the velocity components is found to be directly attributable to the compactness of the initial vorticity.

Criminale, W. O.↗
NASA NTRS1995

Experimental study of the use of vortex generators to reduce fluctuating pressure loads in shock wave turbulent boundary layer interactions

Fluctuating wall pressure measurements have been made in a separated shock wave/turbulent boundary layer interaction produced by an unswept compression corner in a Mach 5 flow. Wheeler doublet vortex generators were placed 15.8 boundary layer thicknesses upstream of the corner to study their effect on the fluctuating pressure loads produced by the translating separation shock. The vortex generators produced significant three-dimensionality in an otherwise two-dimensional interaction. They reduced the upstream influence and the length of the region of shock motion by 60% and 64%, respectively, decreased the maximum wall pressure rms by 23%, and shifted the fluctuations to a higher frequency band. The maximum fraction of energy in the 100-500 Hz frequency band is decreased by 11%. These changes are due to a fuller boundary layer profile, a weaker separation shock, and increased boundary layer turbulence causing increased separation shock jitter.

Barter, John W.↗
NASA NTRS1995

Overview of the preparation and use of an OV-10 aircraft for wake vortex hazards flight experiments

An overview is presented of the development, use, and current flight-test status of a highly instrumented North American Rockwell OV-10A Bronco as a wake-vortex-hazards research aircraft. A description of the operational requirements and measurements criteria, the resulting instrumentation systems and aircraft modifications, system-calibration and research flights completed to date, and current flight status are included. These experiments are being conducted by the National Aeronautics and Space Administration as part of an effort to provide the technology to safely improve the capacity of the nation's air transportation system and specifically to provide key data in understanding and predicting wake vortex decay, transport characteristics, and the dynamics of encountering wake turbulence. The OV-10A performs several roles including meteorological measurements platform, wake-decay quantifier, and trajectory-quantifier for wake encounters. Extensive research instrumentation systems include multiple airdata sensors, video cameras with cockpit displays, aircraft state and control-position measurements, inertial aircraft-position measurements, meteorological measurements, and an on-board personal computer for real-time processing and cockpit display of research data. To date, several of the preliminary system check flights and two meteorological-measurements deployments have been completed. Several wake encounter and wake-decay-measurements flights are planned for the fall of 1995.

Stuever, Robert A.↗
NASA NTRS1996

A preliminary study of a wake vortex encounter hazard boundary for a B737-100 airplane

A preliminary batch simulation study was conducted to define the wake decay required for a Boeing 737-100 airplane to safely encounter a Boeing 727 wake and land. The baseline six-degree-of-freedom B737 simulation was modified to include a wake model and the strip-theory calculation of the vortex-induced forces and moments. The guidance and control inputs for the airplane were provided by an autoland system. The wake strength and encounter altitude were varied to establish a safe encounter boundary. The wake was positioned such that the desired flight path traversed the core of the port Vortex. Various safe landing criteria were evaluated for defining a safe encounter boundary. A sensitivity study was also conducted to assess the effects of encounter model inaccuracies.

Reimer, Heidi M.↗
NASA NTRS1996

Investigation of Drop Formation by a Vortex Ring in Microgravity

An investigation of drop formation by a vortex ring propagating through one or more fluid interfaces in microgravity is described. The main goal of the research is to determine the dynamics of drop formation by vortical flows in the capillary limit with large density change across the intel-face. Dimensional analysis shows that in microgravity experiments the capillary limit can be studied using a relatively large vortex ring diameter to facilitate experimental characterization of the interaction. Results obtained in density matched systems are reviewed to illustrate the complex nature of these interactions.

Bernal, Luis P.↗
NASA NTRS1996

Far-Field Turbulent Vortex-Wake/Exhaust Plume Interaction for Subsonic and HSCT Airplanes

Computational study of the far-field turbulent vortex-wake/exhaust plume interaction for subsonic and high speed civil transport (HSCT) airplanes is carried out. The Reynolds-averaged Navier-Stokes (NS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The two-equation shear stress transport model of Menter is implemented with the NS solver for turbulent-flow calculation. For the far-field study, the computations of vortex-wake interaction with the exhaust plume of a single engine of a Boeing 727 wing in a holding condition and two engines of an HSCT in a cruise condition are carried out using overlapping zonal method for several miles downstream. These results are obtained using the computer code FTNS3D. The results of the subsonic flow of this code are compared with those of a parabolized NS solver known as the UNIWAKE code.

Kandil, Osama A.↗