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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Analysis and Design of Rotors at Ultra-Low Reynolds Numbers

Design tools have been developed for ultra-low Reynolds number rotors, combining enhanced actuator-ring / blade-element theory with airfoil section data based on two-dimensional Navier-Stokes calculations. This performance prediction method is coupled with an optimizer for both design and analysis applications. Performance predictions from these tools have been compared with three-dimensional Navier Stokes analyses and experimental data for a 2.5 cm diameter rotor with chord Reynolds numbers below 10,000. Comparisons among the analyses and experimental data show reasonable agreement both in the global thrust and power required, but the spanwise distributions of these quantities exhibit significant deviations. The study also reveals that three-dimensional and rotational effects significantly change local airfoil section performance. The magnitude of this issue, unique to this operating regime, may limit the applicability of blade-element type methods for detailed rotor design at ultra-low Reynolds numbers, but these methods are still useful for evaluating concept feasibility and rapidly generating initial designs for further analysis and optimization using more advanced tools.

Kunz, Peter J.↗
NASA NTRS1961

Surface Pressures and Heat Transfer on Unswept Blunt Plates in Helium at High Mach Numbers

Pressure distributions and local convective heat-transfer coefficients on a flat plate at zero angle of attack were measured in helium. Data were obtained with various amounts of leading-edge bluntness at Mach numbers of 12.5 and 14.7. The pressures on a sharp leading-edged plate were not influenced by the leading edge and were predicted by the first-order, hypersonic, weak-interaction theory. Pressures on blunt plates were correlated by introducing the leading-edge Reynolds number as a parameter. Measured heat-transfer coefficients on the sharp plate agreed with predictions obtained form existing exact solutions for hear transfer across the laminar boundary layer. For the blunt plates a comparison of theory with experiment indicated that more knowledge of the flow field between the sock wave and plate surface is necessary before an adequate prediction of convective heat transfer can be made. Shock-wave shapes for the blun plates at a Mach number 12.5 and zero angle of attack were measured. At distances between 2 and 60 leading-edge thicknesses from the shock vertex, the shock-wave shapes were found to be represented by a modified form of the blast-wave analogy.

Marvin, Joseph G.↗
NASA NTRS1961

Transonic Wind-Tunnel Investigation of the Static Longitudinal Aerodynamic Characteristics of Several Configurations of the Scout Vehicle and of a Number of Related Models

Results have been obtained i n t h e Langley 8-foot transonic pressure tunnel at Mach numbers from 0.40 t o 1.20 for several configurations of the Scout vehicle and f o r a number of related models. Tests extended over an angle-of-attack range from about -10 degrees to 10 degrees at a Reynolds number per foot of about 3.8 x 10 sup 6.

Kelly, Thomas C.↗
NASA NTRS1961

Investigation of an Axisymmetric Internal Compression Inlet at a Mach Number of About 3.8

An idealized axisymmetric, all-internal compression inlet was designed for a Mach number of 3.75. The objective of the design was to obtain a steady, one-dimensional transonic flow and a high over-all total pressure recovery. Boundary-layer removal was employed in the vicinity of the inflection point of the supersonic contour. Static and total-pressure fluctuations were measured in the transonic flow region. A total pressure recovery of about 90 percent was obtained with a boundary-layer-removal mass flow rate of 15 percent of the inlet mass flow rate. The accompanying root-mean-square total pressure fluctuation in the throat region was only 1 percent of the free stream total pressure. The test Mach number was 3.80 and the Reynolds number based on inlet diameter was 2.63 x 10(exp 6).

Lundell, John H.↗
NASA NTRS2003

Large-Eddy Simulation of Conductive Flows at Low Magnetic Reynolds Number

In this paper we study the LES method with dynamic procedure in the context of conductive flows subject to an applied external magnetic field at low magnetic Reynolds number R(sub m). These kind of flows are encountered in many industrial applications. For example, in the steel industry, applied magnetic fields can be used to damp turbulence in the casting process. In nuclear fusion devices (Tokamaks), liquid-lithium flows are used as coolant blankets and interact with the surrounding magnetic field that drives and confines the fusion plasma. Also, in experimental facilities investigating the dynamo effect, the flow consists of liquid-sodium for which the Prandtl number and, as a consequence, the magnetic Reynolds number is low. Our attention is focused here on the case of homogeneous (initially isotropic) decaying turbulence. The numerical simulations performed mimic the thought experiment described in Moffatt in which an initially homogeneous isotropic conductive flow is suddenly subjected to an applied magnetic field and freely decays without any forcing. Note that this flow was first studied numerically by Schumann. It is well known that in that case, extra damping of turbulence occurs due to the Joule effect and that the flow tends to become progressively independent of the coordinate along the direction of the magnetic field. Our comparison of filtered direct numerical simulation (DNS) predictions and LES predictions show that the dynamic Smagorinsky model enables one to capture successfully the flow with LES, and that it automatically incorporates the effect of the magnetic field on the turbulence. Our paper is organized as follows. In the next section we summarize the LES approach in the case of MHD turbulence at low R(sub m) and recall the definition of the dynamic Smagorinsky model. In Sec. 3 we describe the parameters of the numerical experiments performed and the code used. Section 4 is devoted to the comparison of filtered DNS results and LES results. Conclusions are presented in Sec. 5.

Knaepen, B.↗
NASA NTRS2003

Estimating the k2 Tidal Gravity Love Number of Mars

Analysis of the orbits of spacecraft can be used to infer global tidal parameters. For Mars, the Mars Global Surveyor (MGS) spacecraft has been used to estimate the second degree Love number, k2 from the tracking DSN tracking Doppler and range data by several authors. Unfortunately, neither of the spacecraft presently in orbit are ideally suited to tidal recovery because they are in sun-synchronous orbits that vary only slightly in local time; and, further, the sub-solar location only varies by about 25 degrees in latitude. Never-the less respectable estimates of the k2 tide have been made by several authors. We present an updated solution of the degree 2 zonal Love number, compare with previous dues, and analyze the sensitivity of the solution to orbital parameters, spacecraft maneuvers, and solution methodology. Estimating the k2 Tidal Gravity Love Number of Mars.

Smith, David E.↗
NASA NTRS1960

Effect of Base Bleed and Terminal Fairings on the Performance of Exhaust-Nozzle-Afterbody Combinations at Mach Numbers of 1.93, 2.55, and 3.05

An investigation of four exhaust-nozzle-afterbody combinations has been conducted in the Langley 9- by 12-inch blowdown tunnel at Mach numbers of 1.93, 2.55, and 3.05. The models were tested on a pylon-mounted nacelle and the jet exhaust was simulated with cold air. Base bleed w a s varied from 0 to about 12 percent of the primary jet weight flow and was discharged in to the base region through either a sonic or supersonic bleed nozzle. The models were tested at zero degree angle of attack and the Reynolds number range was from 8 x 10(exp 6) to 9 x 10(exp 6) per foot. The results indicate that the base pressure and the performance of the exhaust-nozzle-afterbody combinations were little affected gy the high-velocity base bleed. The efficiency of the terminal-fairing model was only slightly less than that of the convergent-divergent nozzle-afterbody combinations; this difference indicates the loss associated with improved transonic efficiency at higher Mach numbers.

Norton, Harry T., Jr.↗
NASA NTRS1961

Measurements of Aerodynamic Heat Transfer and Boundary-Layer Transition on a 10 deg Cone in Free Flight at Supersonic Mach Numbers up to 5.9

Measurements of aerodynamic heat transfer have been made at six stations on the 40-inch-long 10 deg. total-angle conical nose of a rocket- propelled model which was flight tested at Mach numbers up to 5.9. are presented for a range of local Mach number just outside the bound- ary layer on the cone from 1.57 to 5.50, and a range of local Reynolds number from 6.6 x 10(exp 6) to 55.2 x 10(exp 6) based on length from the nose tip.

Rumsey, Charles B.↗
NASA NTRS2002

Gravitational unloading effects on muscle fiber size, phenotype and myonuclear number

The effects of gravitational unloading with or without intact neural activity and/or tension development on myosin heavy chain (MHC) composition, cross-sectional area (CSA), number of myonuclei, and myonuclear domain (cytoplasmic volume per myonucleus ratio) in single fibers of both slow and fast muscles of rat hindlimbs are reviewed briefly. The atrophic response to unloading is generally graded as follows: slow extensors > fast extensors > fast flexors. Reduction of CSA is usually greater in the most predominant fiber type of that muscle. The percentage of fibers expressing fast MHC isoforms increases in unloaded slow but not fast muscles. Myonuclear number per mm of fiber length and myonuclear domain is decreased in the fibers of the unloaded predominantly slow soleus muscle, but not in the predominantly fast plantaris. Decreases in myonuclear number and domain, however, are observed in plantaris fibers when tenotomy, denervation, or both are combined with hindlimb unloading. All of these results are consistent with the view that a major factor for fiber atrophy is an inhibition or reduction of loading of the hindlimbs. These data also indicate that predominantly slow muscles are more responsive to unloading than predominantly fast muscles. c2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

Review, Tutorial↗
NASA NTRS1998

The Use of Heavy Gas for Increased Reynolds Numbers in Transonic Wind Tunnels

The use of a high molecular weight test gas to increase the Reynolds number range of transonic wind tunnels is explored. Modifications to a small transonic wind tunnel are described and the real gas properties of the example heavy gas (sulfur hexafluoride) are discussed. Sulfur hexafluoride is shown to increase the test Reynolds number by a factor of more than 2 over air at the same Mach number. Experimental and computational pressure distributions on an advanced supercritical airfoil configuration at Mach 0.7 in both sulfur hexafluoride and nitrogen are presented. Transonic similarity theory is shown to be partially successful in transforming the heavy gas results to equivalent nitrogen (air) results, provided the correct definition of gamma is used.

Anders, J. B.↗
NASA NTRS1997

Parametric Investigation of a High-Lift Airfoil at High Reynolds Numbers

A new two-dimensional, three-element, advanced high-lift research airfoil has been tested in the NASA Langley Research Center s Low-Turbulence Pressure Tunnel at a chord Reynolds number up to 1.6 x 107. The components of this high-lift airfoil have been designed using a incompressible computational code (INS2D). The design was to provide high maximum-lift values while maintaining attached flow on the single-segment flap at landing conditions. The performance of the new NASA research airfoil is compared to a similar reference high-lift airfoil. On the new high-lift airfoil the effects of Reynolds number on slat and flap rigging have been studied experimentally, as well as the Mach number effects. The performance trend of the high-lift design is comparable to that predicted by INS2D over much of the angle-of-attack range. However, the code did not accurately predict the airfoil performance or the configuration-based trends near maximum lift where the compressibility effect could play a major role.

Lin, John C.↗
NASA NTRS2004

Reynolds Number, Compressibility, and Leading-Edge Bluntness Effects on Delta-Wing Aerodynamics

An overview of Reynolds number, compressibility, and leading edge bluntness effects is presented for a 65 degree delta wing. The results of this study address both attached and vortex-flow aerodynamics and are based upon a unique data set obtained in the NASA-Langley National Transonic Facility (NTF) for i) Reynolds numbers ranging from conventional wind-tunnel to flight values, ii) Mach numbers ranging from subsonic to transonic speeds, and iii) leading-edge bluntness values that span practical slender wing applications. The data were obtained so as to isolate the subject effects and they present many challenges for Computational Fluid Dynamics (CFD) studies.

Luckring, James M.↗
NASA NTRS1991

Comparative Flow Path Analysis and Design Assessment of an Axisymmetric Hydrogen Fueled Scramjet Flight Test Engine at a Mach Number of 6.5

NASA has contracted with the Central Institute of Aviation Motors CIAM to perform a flight test and ground test and provide a scramjet engine for ground test in the United States. The objective of this contract is to obtain ground to flight correlation for a supersonic combustion ramjet (scramjet) engine operating point at a Mach number of 6.5. This paper presents results from a flow path performance and thermal evaluation performed on the design proposed by the CIAM. This study shows that the engine will perform in the scramjet mode for stoichiometric operation at a flight Mach number of 6.5. Thermal assessment of the structure indicates that the combustor cooling liner will provide adequate cooling for a Mach number of 6.5 test condition and that optional material proposed by CIAM for the cowl leading-edge design are required to allow operation with or without a type IV shock-shock interaction.

McClinton, C.↗
NASA NTRS2004

High Reynolds Number Thermal Stability Experiments

This work represents preliminary thermal stability results for liquid hydrocarbon fuels. High Reynolds Number Thermal Stability experiments with Jet A and RP-1 resulted in a quantitative measurement of the thermal stability. Each fuel flowed through a heated capillary tube that held the outlet temperature at 290 C. An optical pyrometer measured the surface temperature of the tube at 12 locations as a function of time. The High Reynolds Number Thermal Stability number was then determined using standards published by the American Society for Testing and Materials. The results for Jet A showed lower thermal stability than similar tests conducted at another facility. The RP-1 results are the first reported using this technique. Because the temperature rise on the capillary tube during testing for the RP-1 fuels was not significant, a new standard for the testing conditions should be developed for these types of fuels.

Emens, Jessica M.↗
NASA NTRS1998

The effects of delta rays on the number of particle-track traversals per cell in laboratory and space exposures

It is a common practice to estimate the number of particle-track traversals per cell or cell nucleus as the product of the ion's linear energy transfer (LET) and cell area. This practice ignores the effects of track width due to the lateral extension of delta rays. We make estimates of the number of particle-track traversals per cell, which includes the effects of delta rays using radial cutoffs in the ionization density about an ion's track of 1 mGy and 1 cGy. Calculations for laboratory and space radiation exposures are discussed, and show that the LET approximation provides a large underestimate of the actual number of particle-track traversals per cell from high-charge and energy (HZE) ions. In light of the current interest in the mechanisms of radiation action, including signal transduction and cytoplasmic damage, these results should be of interest for radiobiology studies with HZE ions.

NASA Discipline Radiation Health↗
NASA NTRS1997

Growth hormone/IGF-I and/or resistive exercise maintains myonuclear number in hindlimb unweighted muscles

In the present study of rats, we examined the role, during 2 wk of hindlimb suspension, of growth hormone/insulin-like growth factor I (GH/IGF-I) administration and/or brief bouts of resistance exercise in ameliorating the loss of myonuclei in fibers of the soleus muscle that express type I myosin heavy chain. Hindlimb suspension resulted in a significant decrease in mean soleus wet weight that was attenuated either by exercise alone or by exercise plus GH/IGF-I treatment but was not attenuated by hormonal treatment alone. Both mean myonuclear number and mean fiber cross-sectional area (CSA) of fibers expressing type I myosin heavy chain decreased after 2 wk of suspension compared with control (134 vs. 162 myonuclei/mm and 917 vs. 2,076 micron2, respectively). Neither GH/IGF-I treatment nor exercise alone affected myonuclear number or fiber CSA, but the combination of exercise and growth-factor treatment attenuated the decrease in both variables. A significant correlation was found between mean myonuclear number and mean CSA across all groups. Thus GH/IGF-I administration and brief bouts of muscle loading had an interactive effect in attenuating the loss of myonuclei induced by chronic unloading.

NASA Center ARC↗
NASA NTRS1957

Effects of Inlet Modification and Rocket-Rack Extension on the Longitudinal Trim and Low-Lift Drag of the Douglas F5D-1 Airplane as Obtained with a 0.125-Scale Rocket-Boosted Model between Mach Numbers of 0.81 and 1.64, TED No. NACA AD 399

A flight investigation was conducted to determine the effects of an inlet modification and rocket-rack extension on the longitudinal trim and low-lift drag of the Douglas F5D-1 airplane. The investigation was conducted with a 0.125-scale rocket-boosted model which was flight tested at the Langley Pilotless Aircraft Research Station at Wallops Island, Va. Results indicate that the combined effects of the modified inlet and fully extended rocket racks on the trim lift coefficient and trim angle of attack were small between Mach numbers of 0.94 and 1.57. Between Mach numbers of 1.10 and 1.57 there was an average increase in drag coefficient of about o,005 for the model with modified inlet and extended rocket racks. The change in drag coefficient due to the inlet modification alone is small between Mach numbers of 1.59 and 1.64

Hastings, Earl C., Jr.↗
NASA NTRS1954

Aerodynamic Characteristics at High and Low Subsonic Mach Numbers of the NACA 0012, 64(sub 2)-015, and 64(sub 3)-018 Airfoil Sections at Angles of Attack from -2 Degrees to 30 Degrees

An investigation has been made in the Langley low-turbulence pressure tunnel of the aerodynamic characteristics of the NACA 0012, 64(sub 2)-015, and 64(sub 3)-018 airfoil sections. Data were obtained at Mach numbers from 0.3 to that for tunnel choke, at angles of attack from -2deg to 30deg, and with the surface. of each airfoil smooth-and with roughness applied at the leading edge.The Reynolds numbers of the tests ranged from 0.8 x 10(exp 6) to 4.4 x 10(exp 6). The results are presented as variations of lift, drag, and quarter-chord pitching-moment coefficients with Mach number.

Critzos, Chris C.↗