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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1931

Tests of N.A.C.A. airfoils in the variable-density wind tunnel Series 45 and 65

This note is one of a series covering an investigation of a number of related airfoils. It presents the results obtained from tests in N.A.C.A. Variable-Density Wind Tunnel of two groups of six airfoils each. One group, the 45 series, has a maximum mean camber of 4 per cent of the chord at a position 0.5 of the chord behind the leading edge, and the other group, the 65 series, has a maximum mean camber of 6 per cent of the chord at the same position. The members within each group differ only in maximum thickness, the maximum thickness/chord ratios being: 0.06, 0.09, 0.12, 0.15, 0.18, and 0.21. The results are analyzed with a view to indicating the variation of the aerodynamic characteristics with profile thickness for airfoils having a certain mean camber line form.

Jacobs, Eastman N↗
NASA NTRS1931

Tests of N.A.C.A. airfoils in the variable density wind tunnel Series 44 and 64

This note is one of a series covering an investigation of a number of related airfoils. It presents the results obtained from tests in the N.A.C.A. Variable Density Wind Tunnel of two groups of six airfoils each. One group, the 44 series, has a maximum mean camber of 4 percent of the chord at a position 0.4 of the chord behind the leading edge and the other group, the 64 series, has a maximum mean camber of 6 percent of the chord at the same position. The members within each group differ only in maximum thickness, the maximum thickness/chord ratios being: 0.06, 0.09, 0.12, 0.15, 0.18, and 0.21. The results are analyzed with a view to indicating the variation of the aerodynamic characteristics with profile thickness for airfoils having a certain mean camber line form.

Jacobs, Eastman N↗
NASA NTRS1931

Tests of N.A.C.A. airfoils in the variable-density wind tunnel Series 43 and 63

This note is one of a series covering an investigation of a family of related airfoils. It gives in preliminary form the results obtained from tests in the N.A.C.A. Variable-Density Wind Tunnel of two groups of six airfoils each. One group, the 43 series, has a maximum mean camber of 4 per cent of the chord at a position 0.3 of the chord from the leading edge; the other group, the 63 series, has a maximum mean camber of 6 per cent of the chord at the same position. The members within each group differ only in maximum thickness, the maximum thickness/chord ratios being:0.06, 0.09, 0.12, 0.15, 0.18, and 0.21. The results are analyzed with a view to indicating the variation of the aerodynamic characteristics with profile thickness for airfoils having a certain mean camber line.

Jacobs, Eastman N↗
NASA NTRS1932

Tests of N.A.C.A. airfoils in the variable-density wind tunnel Series 24

This note is the fifth of a series covering an investigation of a number of related airfoils. It presents the results obtained from tests of a group of six low-cambered airfoils in the variable-density wind tunnel. The mean camber lines are identical for the six airfoils and are of such a form that the maximum mean camber is 2 per cent of the chord and is at a position 0.4 of the chord behind the loading edge. The airfoils differ in thickness only, the maximum-thickness/chord ratios being 0.06, 0.09, 0.12, 0.15, 0.18, and 0.21. The results have been presented in the form of both infinite and finite aspect-ratio characteristics. The values of C(sub L) max/C(sub d) degrees min for this group of airfoils are among the highest thus far obtained, the minimum profile drags being approximately equal to those for the symmetrical series of corresponding thickness, while the maximum lift coefficients are considerably higher.

Jacobs, Eastman N↗
NASA NTRS1973

A provisional analysis of two-dimensional turbulent mixing with variable density

A predictive method for the titled flows based on the Prandtl energy method was developed and assessed by comparing predicted results with experimental results. For constant-density flows, both gross properties such as spreading rate and maximum turbulent kinetic energy and detailed properties such as mean shear stress distributions are shown to be well predicted. For variable-density flows, considerable attention is devoted to the inclusion in the analysis of the added effect of pressure fluctuations and of the variation in the several extant empirical parameters on the turbulent kinetic energy. It is found that a variation with Mach number of the characteristic Reynolds number for turbulent transport is needed to account for the observed decrease in spreading rate. The predictions which result from these considerations are compared with the limited experimental data presently available for the two crucial cases: compressible adiabatic mixing and low-speed isothermal mixing of two dissimilar gases.

Libby, P. A.↗
NASA NTRS1931

Large-scale aerodynamic characteristics of airfoils as tested in the variable density wind tunnel

In order to give the large-scale characteristics of a variety of airfoils in a form which will be of maximum value, both for airplane design and for the study of airfoil characteristics, a collection has been made of the results of airfoil tests made at full-scale values of the reynolds number in the variable density wind tunnel of the National Advisory Committee for Aeronautics. They have been corrected for tunnel wall interference and are presented not only in the conventional form but also in a form which facilitates the comparison of airfoils and from which corrections may be easily made to any aspect ratio. An example showing the method of correcting the results to a desired aspect ratio has been given for the convenience of designers. In addition, the data have been analyzed with a view to finding the variation of the aerodynamic characteristics of airfoils with their thickness and camber.

Jacobs, Eastman N↗
NASA NTRS1937

Fuselage-drag tests in the variable-density wind tunnel: streamline bodies of revolution, fineness ratio of 5

Results are presented of the drag tests of six bodies of revolution with systematically varying shapes and with a fineness ratio of 5. The forms were derived from source-sink distributions, and formulas are presented for the calculation of the pressure distribution of the forms. The tests were made in the N.A.C.A. variable-density tunnel over a range of values of Reynolds number from about 1,500,000 to 25,000,000. The results show that the bodies with the sharper noses and tails have the lowest drag coefficients, even when the drag coefficients are based on the two-thirds power of the volume. The data shows the most important single characteristic of the body form to be the tail angle, which must be fine to obtain low drag.

Abbott, Ira H↗
NASA NTRS1931

A comparison of the aerodynamic characteristics of the normal and three reflexed airfoils in the variable density wind tunnel

An investigation was made of the aerodynamic effects of reflexing the trailing edge of three commonly used airfoils. Six airfoils were used in the investigation: three having the normal profiles of the Navy 60, the Boeing 106, and the Gottingen 398, and three having these profiles modified to obtain a reflexed trailing edge with the mean camber line changed to give Cmc/4=0. The tests were conducted at a value of the Reynolds Number of approximately 3,100,000 in the variable density wind tunnel of the National Advisory Committee for Aeronautics. Measurements of lift, drag, and pitching moment were made on each of the six airfoils. The expected reduction of the center of pressure travel was obtained. The maximum lift was reduced approximately 12 per cent and the minimum profile drag approximately 4 per cent.

Defoe, George L↗
NASA NTRS1993

A transport equation for the scalar dissipation in reacting flows with variable density: First results

Although the different regimes of premixed combustion are not well defined, most of the recent developments in turbulent combustion modeling are led in the so-called flamelet regime. The goal of these models is to give a realistic expression to the mean reaction rate (w). Several methods can be used to estimate (w). Bray and coworkers (Libby & Bray 1980, Bray 1985, Bray & Libby 1986) express the instantaneous reaction rate by means of a flamelet library and a frequency which describes the local interaction between the laminar flamelets and the turbulent flowfield. In another way, the mean reaction rate can be directly connected to the flame surface density (Sigma). This quantity can be given by the transport equation of the coherent flame model initially proposed by Marble & Broadwell 1977 and developed elsewhere. The mean reaction rate, (w), can also be estimated thanks to the evolution of an arbitrary scalar field G(x, t) = G(sub O) which represents the flame sheet. G(x, t) is obtained from the G-equation proposed by Williams 1985, Kerstein et al. 1988 and Peters 1993. Another possibility proposed in a recent study by Mantel & Borghi 1991, where a transport equation for the mean dissipation rate (epsilon(sub c)) of the progress variable c is used to determine (w). In their model, Mantel & Borghi 1991 considered a medium with constant density and constant diffusivity in the determination of the transport equation for (epsilon(sub c)). A comparison of different flamelet models made by Duclos et al. 1993 shows the realistic behavior of this model even in the case of constant density. Our objective in this present report is to present preliminary results on the study of this equation in the case of variable density and variable diffusivity. Assumptions of constant pressure and a Lewis number equal to unity allow us to significantly simplify the equation. A systematic order of magnitude analysis based on adequate scale relations is performed on each term of the equation. As in the case of constant density and constant diffusivity, the effects of stretching of the scalar field by the turbulent strain field, of local curvature, and of chemical reactions are predominant. In this preliminary work, we suggest closure models for certain terms, which will be validated after comparisons with DNS data.

Mantel, T.↗
NASA NTRS2001

Large-Scale Liquid Hydrogen Testing of Variable Density Multilayer Insulation with a Foam Substrate

The multipurpose hydrogen test bed (MHTB), with an 18-cu m liquid hydrogen tank, was used to evaluate a combination foam/multilayer combination insulation (MLI) concept. The foam element (Isofoam SS-1171) insulates during ground hold/ascent flight, and allowed a dry nitrogen purge as opposed to the more complex/heavy helium purge subsystem normally required. The 45-layer MLI was designed for an on-orbit storage period of 45 days. Unique WI features include a variable layer density, larger but fewer double-aluminized Mylar perforations for ascent to orbit venting, and a commercially established roll-wrap installation process that reduced assembly man-hours and resulted in a roust, virtually seamless MLI. Insulation performance was measured during three test series. The spray-on foam insulation (SOFI) successfully prevented purge gas liquefaction within the MLI and resulted in the expected ground hold heat leak of 63 W/sq m. The orbit hold tests resulted in heat leaks of 0.085 and 0.22 W/sq m with warm boundary temperatures of 164 and 305 K, respectively. Compared to the best previously measured performance with a traditional MLI system, a 41-percent heat leak reduction with 25 fewer MLI layers was achieved. The MHTB MLI heat leak is half that calculated for a constant layer density MLI.

Martin, J. J.↗
NASA NTRS1987

Mesoscale density variability in the mesosphere and thermosphere: Effects of vertical flow accelerations

A mechanistic one dimensional numerical (iteration) model was developed which can be used to simulate specific types of mesoscale atmospheric density (and pressure) variability in the mesosphere and the thermosphere, namely those due to waves and those due to vertical flow accelerations. The model was developed with the idea that it could be used as a supplement to the TGCMs (thermospheric general circulation models) since such models have a very limited ability to model phenomena on small spatial scales. The simplest case to consider was the integration upward through a time averaged, height independent, horizontally divergent flow field. Vertical winds were initialized at the lower boundary using the Ekman pumping theory over flat terrain. The results of the computations are summarized.

Revelle, D. O.↗
NASA NTRS1981

Cloud encounter and particle density variabilities from GASP data

Summary statistics and variability studies are presented for cloud encounter and particle number density data as part of the NASA Global Atmospheric Sampling Program (GASP) aboard commercial Boeing 747 airliners. On the average, cloud encounter is shown on about 15% of the 52,164 data samples available; this value varies with season, latitude, synoptic weather situation, and distance from the tropopause. The number density of particles (diameter greater than 3 microns) also varies with time and location, and depends on the horizontal extent of cloudiness.

Nastrom, G. D.↗
NASA NTRS2000

Variable Density Multilayer Insulation for Cryogenic Storage

Two analytical models for a foam/Variable Density Multi-Layer Insulation (VD-MLI) system performance are discussed. Both models are one-dimensional and contain three heat transfer mechanisms, namely conduction through the spacer material, radiation between the shields, and conduction through the gas. One model is based on the methodology developed by McIntosh while the other model is based on the Lockheed semi-empirical approach. All models input variables are based on the Multi-purpose Hydrogen Test Bed (MHTB) geometry and available values for material properties and empirical solid conduction coefficient. Heat flux predictions are in good agreement with the MHTB data, The heat flux predictions are presented for the foam/MLI combinations with 30, 45, 60, and 75 MLI layers

Hedayat, A.↗
NASA NTRS1972

Continuous-flow variable-density wind tunnel facilities

Unique features of wind tunnel facilities at Jet Propulsion Laboratory permit variety of conventional and novel tests to be performed at supersonic and hypersonic speeds. Facilities and operations are described.

Herrera, J. G.↗