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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Supersonic quiet-tunnel development for laminar-turbulent transition research

This grant supported research into quiet-flow supersonic wind-tunnels, between February 1994 and February 1995. Quiet-flow nozzles operate with laminar nozzle-wall boundary layers, in order to provide low-disturbance flow for studies of laminar-turbulent transition under conditions comparable to flight. Major accomplishments include: (1) development of the Purdue Quiet-Flow Ludwieg Tube, (2) computational evaluation of the square nozzle concept for quiet-flow nozzles, and (3) measurement of the presence of early transition on the flat sidewalls of the NASA LaRC Mach 3.5 supersonic low-disturbance tunnel. Since items (1) and (2) are described in the final report for companion grant NAG1-1133, only item (3) is described here. A thesis addressing the development of square nozzles for high-speed, low-disturbance wind tunnels is included as an appendix.

Schneider, Steven P.↗
NASA NTRS1994

Observations of Laminar Surface Shear Stress Patterns on the Sidewall of a Rectangular, Mach 3 Quiet Tunnel Using Liquid Crystal Coatings

A shear-stress--sensitive liquid crystal coating (LCC) was used to visualize the surface shear stress distribution on the flat sidewall of the MSU quiet supersonic tunnel as a function of flow stagnation pressure. Under conditions of quiet operation, the LCC color-change response indicated the existence of a nonuniform surface shear stress distribution. This shear pattern was characterized by an elongated, down st ream-point ing triangular region of relatively low shear, with its apex on and its axis coincident with, the sidewall centerline. This low-shear zone was bounded symmetrically by two regions of relatively higher shear; these high-shear zones originated within the concave-curvature portion of the nozzle, in the corners between the flat sidewall and the contoured upper and lower nozzle surfaces. A 3-D Navier-Stokes code was used to compute the pressure and surface shear distributions on the sidewall. Flow-expansion-induced transverse pressure gradients on the nozzle sidewall generated symmetric inflows from the corners towards the sidewall centerline; these inflows caused a thickening of the sidewall boundary layer along the centerline, resulting in lower shear stresses consistent with the liquid crystal results. Peripherally nonuniform laminar boundary layer development, and the associated stability of such complex 3-D flows, must be considered in quiet-tunnel applications using rectangular nozzles. A color video will be shown.

Reda, D.↗
NASA NTRS1998

Method and apparatus for reducing the drag of flows over surfaces

An apparatus, and its accompanying method, for reducing the drag of flows over a surface includes arrays of small disks and sensors. The arrays are embedded in the surface and may extend above, or be depressed below, the surface, provided they remain hydraulically smooth either when operating or when inactive. The disks are arranged in arrays of various shapes, and spaced according to the cruising speed of the vehicle on which the arrays are installed. For drag reduction at speeds of the order of 30 meters/second, preferred embodiments include disks that are 0.2 millimeter in diameter and spaced 0.4 millimeter apart. For drag reduction at speeds of the order of 300 meters/second, preferred embodiments include disks that are 0.045 millimeter in diameter and spaced 0.09 millimeter apart. Smaller and larger dimensions for diameter and spacing are also possible. The disks rotate in the plane of the surface, with their rotation axis substantially perpendicular to the surface. The rotating disks produce velocity perturbations parallel to the surface in the overlying boundary layer. The sensors sense the flow at the surface and connect to control circuitry that adjusts the rotation rates and duty cycles of the disks accordingly. Suction and blowing holes can be interspersed among, or made coaxial with, the disks for creating general three-component velocity perturbations in the near-surface region. The surface can be a flat, planar surface or a nonplanar surface, such as a triangular riblet surface. The present apparatus and method have potential applications in the field of aeronautics for improving performance and efficiency of commercial and military aircraft, and in other industries where drag is an obstacle, including gas and oil delivery through long-haul pipelines.

Keefe, Laurence R.↗
NASA NTRS1992

Measurements of the flow around a lifting-wing/body junction

Detailed measurements of all three mean velocity components and five of the six Reynolds stresses have been made around a model of a lifting-wing/body junction. The body was the flat working section floor of a small blower wind tunnel. Measurements of the surface pressure distribution on the NACA 0012 wing showed that the lift coefficient at the body surface was reduced by only 16 percent from the freestream value. It is shown that the near constancy of the bound vorticity requires the formation of aixal vorticity within the body boundary layer. This vorticity was concentrated in the two legs of the necklace vortex formed near the leading edge of the wing. The magnitude of the vorticity was always greater in the leg that developed on the suction surface. By four chord lengths downstream of the trailing edge, the turbulence structure of the suction leg was qualitatively similar to that of a single vortex imbedded in a turbulent boundary layer.

Wood, D. H.↗
NASA NTRS1994

HST eclipse mapping of dwarf nova OY Carinae in quiescence: An 'Fe II curtain' with Mach approx. = 6 velocity dispersion veils the white dwarf

Hubble Space Telescope (HST) observations of the eclipsing dwarf nova OY Car in its quiescent state are used to isolate the ultraviolet spectrum (1150-2500 A at 9.2 A Full Width at Half Maximum (FWHM) resolution) of the white dwarf, the accretion disk, and the bright spot. The white dwarf spectrum has a Stark-broadened photospheric L(alpha) absorption, but is veiled by a forest of blended Fe II features that we attribute to absorption by intervening disk material. A fit gives T(sub w) approx. = 16.5 x 10(exp 3) K for the white dwarf with a solar-abundance, log g = 8 model atmosphere, and T approx. = 10(exp 4) K, n(sub e) approx. = 10(exp 13)/cu cm, N(sub H) approx. = 10(exp 22) sq cm, and velocity dispersion delta V approx. = 60 km/s for the veil of homogeneous solar-abundance local thermodynamic equilibrium (LTE) gas. The veil parameters probably measure characteristic physical conditions in the quiescent accretion disk or its chromosphere. The large velocity dispersion is essential for a good fit; it lowers (chi square)/778 from 22 to 4. Keplerian shear can produce the velocity dispersion if the veiling gas is located at R approx. = 5 R(sub W) with (delta R)/R approx. = 0.3, but this model leaves an unobscured view to the upper hemisphere of the white dwarf, incompatible with absorptions that are up to 80% deep. The veiling gas may be in the upper atmosphere of the disk near its outer rim, but we then require supersonic (Mach approx. = 6) but sub-Keplerian (delta V/V(sub Kep) approx. = 0.07) velocity disturbances in this region to produce both the observed radial velocity dispersion and vertical motions sufficient to elevate the gas to z/R = cos i = 0.12. Such motions might be driven by the gas stream, since it may take several Kepler periods to reestablish the disk's vertical hydrostatic equilibrium. The temperature and column density of the gas we see as Fe II absorption in the ultraviolet are similar to what is required to produce the strong Balmer jump and line emissions seen in optical spectra of OY Car and similar quiescent dwarf novae. The outer accretion disk is detected at mid-eclipse with a spectrum that rises from 0.05 to 0.3 mJy between 2000 and 2500 A, consistent with combinations of cool blackbodies, blended Fe II emission lines, and Balmer continuum emission. The total disk flux density is 0.5 mJy at 2500 A, and this shallow disk eclipse implies a roughly flat surface brightness distribution. The bright spot, somewhat bluer than the disk, has a flux density rising from 0.05 to 0.15 mJy between 1600 and 2500 A. The C IV emission line has a broad shallow eclipse, but the radial velocity variations observed during the eclipse do not clearly distinguish between a disk or wind origin. The only possible indications of boundary layer emission are fast UV flares that appear to arise from near the central object -- not from the bright spot.

Horne, Keith↗
NASA NTRS1982

IUE observations of the peculiar star RX Puppis

The first set of high-dispersion UV observations of RX Pup are presented. Anomalous line profile structure observed in a number of high-excitation emission lines is discussed in context with a model that includes streams and complex mass motions in the system. Anomalies in high-excitation lines suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The continuum in low dispersion is fairly flat around 1200-2000 and rises toward longer wavelengths, and cannot be due to a star earlier than A0 II. Alternatively, it may be from an accretion disk. Photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature 75,000-90,000 K. Alternatively, it may be due to an accretion disk around a secondary with boundary layer temperature about 100,000 K.

Kafatos, M.↗
NASA NTRS1975

The NATA code: Theory and analysis, volume 1

A computer program for calculating quasi-one-dimensional gas flow in axisymmetric and two-dimensional nozzles and rectangular channels is presented. Flow is assumed to start from a state of thermochemical equilibrium at a high temperature in an upstream reservoir. The program provides solutions based on frozen chemistry, chemical equilibrium, and nonequilibrium flow with finite reaction rates. Electronic nonequilibrium effects can be included using a two-temperature model. An approximate laminar boundary layer calculation is given for the shear and heat flux on the nozzle wall. Boundary layer displacement effects on the inviscid flow are considered also. Chemical equilibrium and transport property calculations are provided by subroutines. The code contains precoded thermochemical, chemical kinetic, and transport cross section data for high-temperature air, CO2-N2-Ar mixtures, helium, and argon. It provides calculations of the stagnation conditions on axisymmetric or two-dimensional models, and of the conditions on the flat surface of a blunt wedge. The primary purpose of the code is to describe the flow conditions and test conditions in electric arc heated wind tunnels.

Bade, W. L.↗
NASA NTRS1989

Asymmetrical boundary layer separation at the base of a two cylinder geometry

This paper reports on the experimental description of the three-dimensional horseshoe vortex system occurring at the base of two cylinder mounted side by side on an endwall. The spacing between the two cylinders is adjusted to generate a family of viscous flows. Flow visualization performed in a water tunnel provides a qualitative understanding of the flow over a range of flow variables. A detailed wind tunnel experiment provides a quantitative description of the flow at a single test condition. At Re(D) = 2.5 x 10 to the 5th the measurements show an asymmetrical primary vortex with a wide flat cross section. A small counterrotating vortex is found between the primary vortex and the cylinder leading edge.

Boyle, M. T.↗
NASA NTRS1982

Feasibility of SPF/DB titanium sandwich for LFC wings

The feasibility of fabricating SPF/DB titanium structures of sufficient smoothness to be used for laminar flow wing surfaces was demonstrated. Two methods of fabricating panels which meet the surface smoothness criteria were demonstrated. The first consists of superplasticity forming/diffusion bonding a panel using steel dies, then machining the surface to the required flatness and finish after forming. This approach, however, was estimated to be more costly than the second approach, in which the panel is formed against ceramic platens which produce the desired surface smoothness without subsequent finishing. Four panels were fabricated, and their surface quality was evaluated. The specified criteria for waviness compared with actual measured values on the panels is shown. The acceptable surface quality as well as feasibility of the laminar flow control surface design, in which separate strips incorporating the boundary layer bleed provisions are bonded into slots on the surface, was also demonstrated.

Mcquilkin, F. T.↗
NASA NTRS1996

A Numerical Experiment on the Role of Surface Shear Stress in the Generation of Sound

The sound generated due to a localized flow over an infinite flat surface is considered. It is known that the unsteady surface pressure, while appearing in a formal solution to the Lighthill equation, does not constitute a source of sound but rather represents the effect of image quadrupoles. The question of whether a similar surface shear stress term constitutes a true source of dipole sound is less settled. Some have boldly assumed it is a true source while others have argued that, like the surface pressure, it depends on the sound field (via an acoustic boundary layer) and is therefore not a true source. A numerical experiment based on the viscous, compressible Navier-Stokes equations was undertaken to investigate the issue. A small region of a wall was oscillated tangentially. The directly computed sound field was found to to agree with an acoustic analogy based calculation which regards the surface shear as an acoustically compact dipole source of sound.

Shariff, Karim↗
NASA NTRS1980

Controlled supercritical crossflow on supersonic wings - An experimental validation

Leading edges of wings with high lift at supersonic speeds are discussed. Under these conditions, the leading edge must generate a controlled supercritical crossflow such that high lift is obtained without boundary layer separation. The leading edge concept that accomplishes this is the supersonic counterpart of the leading edge of the 2-D supercritical airfoil at transonic speeds. Wind tunnel test results on a cambered wing with a controlled supercritical crossflow leading edge successfully validated the concept. The main results are presented at the M = 1.62 design point, with off-design results given for the range of Mach numbers from 1.60 to 2.00. Surface pressure, oil flow photographs, and force data are presented and analyzed. A flat wing with the same thickness distribution was also tested and the results were used both for comparison with the designed wing and to illustrate the development of the supercritical crossflow region which, for the flat wing, is terminated by a distinct crossflow shock wave.

Mason, W. H.↗
NASA NTRS1976

Skin friction on a flat perforated acoustic liner

The report concerns the measurement of friction coefficients of a typical perforated acoustic liner installed in the side of a wind tunnel. The results are compared with measured friction coefficients of a smooth hard wall for the same mean flow velocities in a wind tunnel. At a velocity of 61 m/sec, an increase in the local skin coefficient of only a few percent was observed, but at the highest velocity of 213 m/sec an increase of about 20% was obtained. This velocity is a realistic velocity for turbo-machinery components utilizing such liners, so a loss in performance is to be expected. Some tests were also performed to see if changes in the mean boundary layer induced by imposed noise would result in friction increase, but only at low velocity levels was such an increase in friction noted.

Boldman, D. R.↗
NASA NTRS1993

Shallow crustal discontinuities and graben and scarp formation in the Tharsis region of Mars

We recently obtained photoclinometric profiles across all simple grabens and erosional landforms (e.g., troughs, pits, wall-valley heads, and scarps that are bounded above and below by flat surfaces) that occur within Tempe Terra. These data, together with similar data that we obtained for Syria, Sinai, and Lunae Plana and the Alba Patera region, allow regional examination of shallow crust Al discontinuities between latitude 30 deg. S and 50 deg. N and longitude 50 deg. W and 112 deg. W. The profile for each simple graben was used with an appropriate structural model to estimate the depth to the base of the faulted layer. The depths of erosional wall scarps may also indicate the depths of mechanical discontinuities such as a local lithologic or cryospheric boundary. Examination of these data indicates a surprisingly consistent set of shallow crust Al discontinuities for the Tharsis region at depths of 0.4-0.6 km, 1.0-1.4 km, and 2 km; the maximum depth of the features in most study areas appears to be about 4 km. The concentration of values between 0.4 and 0.6 km in most scarp and some faulted-layer depth data is similar to the range in estimated thicknesses of individual exposed Noachian and Hesperian plains units in the Tharsis region. The regional depth data also show two modes near 1 and 2 km in some study areas and a maximum depth near 4 km in most study areas; the faulted-layer depths in excess of 4 km at Alba Patera occur near the summit of the caldera and could be attributed to volcanic loading. Our detailed examination of these depth data includes the following observations: (1) The mode at 1.0-1.4 km depth transcends age and geologic setting in this broad study area; (2) The 2-km mode is most obvious at Alba Patera and moderately well developed at Syria and Sinai Plana, but it is muted at Tempe Terra, which is in the same latitude range as Alba Patera but older; and (3) The 2-km-depth mode is not present in all areas that have features of Amazonian age. We suggest two possible explanations for our observations in the Tharsis region.

Davis, P. A.↗
NASA NTRS1974

Wind tunnel investigation of a large-scale semispan model with an unswept wing and an upper-surface blown jet flat

An investigation of the static longitudinal aerodynamic characteristics of a large-scale semispan model with an unswept wing and an upper-surface blown jet flap for lift augmentation was conducted in the Langley full-scale tunnel. The wing had an aspect ratio of 7.8 (3.9 for the semispan) and a simulated turbofan engine mounted ahead of and above the wing in a nacelle with a rectangular-exit nozzle. The flap system had three spanwise flap segments: (1) an inboard plain flap located behind the engine and having a large radius of curvature to provide a smooth upper surface to enhance the turning of the jet sheet, (2) a double-slotted midspan flap, and (3) a drooped aileron equipped with blowing boundary-layer control. The wing was also equipped with a full-span leading-edge Krueger flap with blowing boundary-layer control. In addition to the aerodynamic measurements, noise measurements were also included in the investigation for positions above and below the wing.

Smith, C. C., Jr.↗
NASA NTRS2004

LiNbO3 Cylinder Fiber

We have successfully fabricate optical fiber with a thin layer of LiNbO3 at the boundary of the glass core and clear glass cladding. The construction of this fiber is based on our successful Semiconductor Cylinder Fibers (SCF). A schematic representation of a LiN bo, Cylinder Fiber. These fibers can be used as light modulators, sonar detectors and in other applications. The core diameter of the fiber is sufficiently small compared to the light wavelength and the indices of refraction of the core and cladding glasses are sufficiently close in value so that there is sufficient light at the core cladding boundary to interact with the LiNbO3 layer. This fiber functions best when just a single light mode propagates through the fiber. The idea for a LiNbO3 Cylinder Fiber came from Dr. Tracee Jamison of NASA. The optical properties of LiNbO3 can be changed with strain or the application of an electric field. Thus these fibers can be used as acoustic sensors as for example in a sonar. They can also be used as electric field operated light modulators. However, for this application the fibers would be made with a cross section in the form of a "D". The core with its surrounding LiNbO, layer would be close to the flat portion of the "D" shaped fiber. Two metal contacts would be deposited on the flat portion of the fiber on either side of the core. A voltage applied across these contacts will result in an electric field in the core region that can be used for modulating the optical properties of the LiNbO3 layer. To our knowledge this is the first ever LiNbO3 Cylinder Fiber made.

Kornreich, Philip↗
NASA NTRS2004

LiNbO3 Cylinder Fiber

We have successfully fabricate optical fiber with a thin layer of LiNbO3 at the boundary of the glass core and dear glass cladding. The construction of this fiber is based on our successful Semiconductor Cylinder Fibers (SCF). A schematic representation of a LiNbO3 Cylinder Fiber is shown. These fibers can be used as light modulators, sonar detectors and in other applications. The core diameter of the fiber is sufficiently small compared to the light wavelength and the indices of refraction of the core and cladding glasses are sufficiently close in value so that there is sufficient light at the core cladding boundary to interact with the LiNbO3 layer. This fiber functions best when just a single light mode propagates through the fiber. The idea for a LiNbO3 Cylinder Fiber came from Dr. Tracee Jamison of NASA. The optical properties of LiNbO3 can be changed with strain or the application of an electric field. Thus these fibers can be used as acoustic sensors as for example in a sonar. They can also be used as electric field operated light modulators. However, for this application the fibers would be made with a cross section in the form of a 'D'. The core with its surrounding LiNbO, layer would be close to the flat portion of the 'D' shaped fiber. Two metal contacts would be deposited on the flat portion of the fiber on either side of the core. A voltage applied across these contacts will result in an electric field in the core region that can be used for modulating the optical properties of the LiNbO, layer. To our knowledge this is the first ever LiNbO, Cylinder Fiber made.

Source record↗
NASA NTRS2012

Vibroacoustic Characterization of a New Hybrid Wing-Body Fuselage Concept

A lighter, more robust airframe design is required to withstand the loading inherent to next generation non cylindrical commercial airliners. The Pultruded Rod Stitched Efficient Unitized Structure concept, a highly integrated composite design involving a stitched and co-cured substructure, has been developed to meet such requirements. While this structure has been shown to meet the demanding out-of-plane loading requirements of the flat-sided pressurized cabin design, there are concerns that the stiff co-cured details will result in relatively high acoustic radiation efficiencies at frequencies well below the thin skin acoustic coincidence frequency. To address this concern and establish a set of baseline vibroacoustic characteristics, a representative test panel was fabricated and a suite of tests were conducted that involved measurements of panel vibration and radiated sound power during point force and diffuse acoustic field excitations. Experimental results are shown and compared with Finite Element and Statistical Energy Analysis model predictions through the use of modal and energy correlation techniques among others. The behavior of the structure subject to turbulent boundary layer excitation is also numerically examined.

Allen, Albert R.↗
NASA NTRS1992

Direct numerical simulation of instabilities in parallel flow with spherical roughness elements

Results from a direct numerical simulation of laminar flow over a flat surface with spherical roughness elements using a spectral-element method are given. The numerical simulation approximates roughness as a cellular pattern of identical spheres protruding from a smooth wall. Periodic boundary conditions on the domain's horizontal faces simulate an infinite array of roughness elements extending in the streamwise and spanwise directions, which implies the parallel-flow assumption, and results in a closed domain. A body force, designed to yield the horizontal Blasius velocity in the absence of roughness, sustains the flow. Instabilities above a critical Reynolds number reveal negligible oscillations in the recirculation regions behind each sphere and in the free stream, high-amplitude oscillations in the layer directly above the spheres, and a mean profile with an inflection point near the sphere's crest. The inflection point yields an unstable layer above the roughness (where U''(y) is less than 0) and a stable region within the roughness (where U''(y) is greater than 0). Evidently, the instability begins when the low-momentum or wake region behind an element, being the region most affected by disturbances (purely numerical in this case), goes unstable and moves. In compressible flow with periodic boundaries, this motion sends disturbances to all regions of the domain. In the unstable layer just above the inflection point, the disturbances grow while being carried downstream with a propagation speed equal to the local mean velocity; they do not grow amid the low energy region near the roughness patch. The most amplified disturbance eventually arrives at the next roughness element downstream, perturbing its wake and inducing a global response at a frequency governed by the streamwise spacing between spheres and the mean velocity of the most amplified layer.

Deanna, R. G.↗