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NASA NTRS1993

Image registration for luminescent paint applications

The use of pressure sensitive luminescent paints is a viable technique for the measurement of surface pressure on wind tunnel models. This technique requires data reduction of images obtained under known as well as test conditions and spatial transformation of the images. A general transform which registers images to subpixel accuracy is presented and the general characteristics of transforms for image registration and their derivation are discussed. Image resection and its applications are described. The mapping of pressure data to the three dimensional model surface for small wind tunnel models to a spatial accuracy of 0.5 percent of the model length is demonstrated.

Bell, James H.↗

NASA NTRS1924

The effect of wind tunnel turbulence upon the forces measured on models

1. Reasons for inquiry: The tests were undertaken to find the effect of turbulence in the air stream upon the lift and drag forces measured on models in the four-foot wind tunnel at the Massachusetts Institute of Technology. 2. Range of investigation: Maximum lifts and minimum drags were measured on Gottingen-387 and R.A.F.-15 airfoils, minimum drag on a streamlined strut, and the static pressure gradients for different conditions of turbulence. 3. Results and further developments: The results show that the scale of the turbulence (as defined in this report) has a marked effect upon the measured forces on models tested in the tunnel as well as on the pressure gradient, and it is recommended that further investigation of the phenomena be made with the aid of smoke and small wind vanes.

Lepage, W L↗

NASA NTRS2011

Wind and Temperature Spectrometry of the Upper Atmosphere in Low-Earth Orbit

Wind and Temperature Spectrometry (WATS) is a new approach to measure the full wind vector, temperature, and relative densities of major neutral species in the Earth's thermosphere. The method uses an energy-angle spectrometer moving through the tenuous upper atmosphere to measure directly the angular and energy distributions of the air stream that enters the spectrometer. The angular distribution gives the direction of the total velocity of the air entering the spectrometer, and the energy distribution gives the magnitude of the total velocity. The wind velocity vector is uniquely determined since the measured total velocity depends on the wind vector and the orbiting velocity vector. The orbiting spectrometer moves supersonically, Mach 8 or greater, through the air and must point within a few degrees of its orbital velocity vector (the ram direction). Pointing knowledge is critical; for example, pointing errors 0.1 lead to errors of about 10 m/s in the wind. The WATS method may also be applied without modification to measure the ion-drift vector, ion temperature, and relative ion densities of major ionic species in the ionosphere. In such an application it may be called IDTS: Ion-Drift Temperature Spectrometry. A spectrometer-based coordinate system with one axis instantaneously pointing along the ram direction makes it possible to transform the Maxwellian velocity distribution of the air molecules to a Maxwellian energy-angle distribution for the molecular flux entering the spectrometer. This implementation of WATS is called the gas kinetic method (GKM) because it is applied to the case of the Maxwellian distribution. The WATS method follows from the recognition that in a supersonic platform moving at 8,000 m/s, the measurement of small wind velocities in the air on the order of a few 100 m/s and less requires precise knowledge of the angle of incidence of the neutral atoms and molecules. The same is true for the case of ion-drift measurements. WATS also provides a general approach that can obtain non-equilibrium distributions as may exist in the upper regions of the thermosphere, above 500 km and into the exosphere. Finally, WATS serves as a mass spectrometer, with very low mass resolution of roughly 1 part in 3, but easily separating atomic oxygen from molecular nitrogen.

Herrero, Federico↗

NASA NTRS2013

Thickness and Fuel Preheating Effects on Material Flammability in Microgravity from the BASS Experiment

The Burning and Suppression of Solids (BASS) experiment was performed on the International Space Station. Microgravity combustion tests burning thin and thick flat samples, acrylic spheres, and candles were conducted. The samples were mounted inside a small wind tunnel which could impose air flow speeds up to 40 cms. The wind tunnel was installed in the Microgravity Science Glovebox which supplied power, imaging, and a level of containment. The effects of air flow speed, fuel thickness, fuel preheating, and nitrogen dilution on flame appearance, flame growth, and spread rates were determined in both the opposed and concurrent flow configuration. In some cases, a jet of nitrogen was introduced to attempt to extinguish the flame. Microgravity flames were found to be especially sensitive to air flow speed in the range 0 to 5 cms. The gas phase response is much faster compared to the solid and so as the flow speed is changed, the flame responds with almost no delay. At the lowest speeds examined (less than 1 cms) all the flames tended to become dim blue and very stable. However, heat loss at these very low convective rates is small so the flames can burn for a long time. At moderate flow speeds (between about 1 and 5 cms) the flame continually heats the solid fuel resulting in an increasing fuel temperature, higher rate of fuel vaporization, and a stronger, more luminous flame as time progresses. Only the smallest flames burning acrylic slabs appeared to be adversely influenced by solid conductive heat loss, but even these burned for over 5 minutes before self-extinguishing. This has implications for spacecraft fire safety since a tiny flame might be undetected for a long time. While the small flame is not particularly hazardous if it remains small, the danger is that it might flare up if the air convection is suddenly increased or if the flame spreads into another fuel source.

Combustion↗

NASA NTRS1976

Mach 4 free-jet tunnel starting experiments for a hypersonic research engine model causing high blockage

Tests of a full scale hypersonic research engine (HRE) were conducted in the hypersonic tunnel facility at Mach numbers of 5, 6, and 7. Since the HRE would cause a rather high blockage (48.83 percent of the nozzle area), subscale tests were conducted in various available small wind tunnels prior to the full scale tests to study the effects of model blockage on tunnel starting. The results of the Mach 4 subscale tests which utilized a model system at 0.0952 scale which simulated the HRE in the test section of the tunnel are presented. A satisfactory tunnel starting could not be achieved by varying the free jet length or diffuser size nor by inserting the model into the test stream after tunnel starting. However, the installation of a shroud around the HRE model allowed the tunnel to start with the model preset in the tunnel at a tunnel stagnation pressure to atmospheric exit pressure ratio of 13.4. The simulation of the discharge of instrumentation cooling water and the addition of test hardware at the aft end of the HRE model did not have a significant effect on the tunnel starting.

Carson, G. T., Jr.↗

NASA NTRS1976

Stall flutter and nonlinear divergence of a two-dimensional flat plate wing

Tests were conducted in a small wind tunnel to study the torsional stall flutter behavior of a two-dimensional flat-plate wing pivoted about the midchord. The nonlinear static divergence equilibrium properties of the wing were well predicted from the measured static moment characteristics. Large amplitude limit cycles ranging from plus or minus 11 degrees to plus or minus 100 degrees were observed. Stall flutter occurred above a critical value of a reduced frequency of about 2. Self-excitation occurred for initial angles of attack between 0 and 8 degrees. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees.

Dugundji, J.↗

NASA NTRS1977

Viscous effects in aircraft trailing vortices

The mechanism of merging of like-signed aircraft vortices leading to a rapid redistribution of trailed vorticity in a wake through both convective and turbulent processes was investigated. Research was done experimentally in a small wind tunnel and analytically through the use of a code which computes turbulent transport using a second-order closure turbulent model. Computations are reported which demonstrate the merging phenomenon, and comparisons are made with experimental results. The usefulness of point vortex computations in predicting merging was explored. Limited computations showed that jet exhaust does not appreciably alter the merging phenomenon. The effect of ambient atmospheric turbulence on the aging of an aircraft wake was investigated at a constant turbulent dissipation rate. It was shown that under stable atmospheric conditions, when atmospheric macroscales are less than or equal to the vortex spacing, misleading results may be obtained.

Bilanin, A. J.↗

NASA NTRS1982

Comparison of winds in the Small Magellanic Cloud and galactic early-type stars

IUE low-resolution spectra of 11 OB stars in the Small Magellanic Cloud reveal considerably lower wind velocities than corresponding galactic stars. The reduced effectiveness of radiative acceleration due to lower abundances of heavy elements in the SMC is believed to be responsible for this effect. The absorption strengths of the SMC P Cygni profiles are somewhat weaker in Si IV and much weaker in C IV. Crude estimates of relative mass-loss rates suggest that the observed differences may be dominated by the differing relative abundances of Si and C, although a lower degree of wind ionization or lower mass-loss rates for the SMC stars cannot be ruled out.

Bruhweiler, F. C.↗

NASA NTRS1982

Wakes from arrays of buildings

Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangements of buildings to maximize light safety.

Logan, E., Jr.↗

NASA NTRS1983

Wakes from arrays of buildings

Logan, E., Jr.↗

NASA NTRS1987

An investigation of the causes of failure of flexible thermal protection materials in an aerodynamic environment

Tests of small panels of advanced flexible reusable surface insulation (AFRSI) were conducted using a small wind tunnel that was designed to simulate Space Shuttle Orbiter entry mean-flow and pulsating aerodynamic loads. The wind tunnel, with a 3 inch wide by 1.75 inch high by 7.5 inch long test section, proved to be capable of continuous flow at dynamic pressures q near 580 psf with fluctuating pressures over 2 psi RMS at an excitation frequency f sub E of 200 Hz. For this investigation, however, the wind tunnel was used to test entry-temperature preconditioned and heat-cleaned AFRSI at q = 280 psf, Prms was nearly equal to 1.2 psi and f sub E = 200 Hz. The objective of these tests was to determine the mechanism of failure of AFRSI at Orbiter entry conditions. Details of the test apparatus and test results are presented.

Coe, Charles F.↗

NASA NTRS1990

Design of a three-component wall-mounted balance

The design and evaluation of a three-component, wall-mounted pyramidal balance for a small wind tunnel is discussed. The balance was designed to measure lift, drag, pitching moment, and angle of attack. The specific design of each component and mathematical models used to design the balance are covered. Balance evaluation consisted of calibration, tare, and interaction analysis.

Winkelmann, Allen E.↗

NASA NTRS1990

Relating evaporative fraction to remotely sensed data at the FIFE site

Evaporative fractions at surface flux stations on the Konza Prairie are investigated by means of heat-flux estimation, evaporative fractions, and other remotely sensed parameters. Radiometric surface-temperature measurements are used to calculate sensible heat, and evaporative fraction is characterized by comparing systematic differences and consistencies at 21 stations. The evaporative fractions are related to soil and vegetation data collected concurrently with attention given to specific correlations. Little variation is found in the evaporative fraction during the day for the four periods studied, although the most significant change corresponded with the lowest values of soil moisture, leaf-area indices, and simple ratio. Uncertainties in air/surface temperature differences and in small wind speeds affect the reliability of estimates of the surface fluxes.

Gurney, R. J.↗

NASA NTRS1990

Modeling cumulus convection with a one-dimensional updraft core model

A model developed for use in satellite rainfall retrievals and possibly useful in other areas of research such as in the development of cloud microphysical schemes or in the study of acid rain, is described. This model is unique in that it models explicitly only a small region about the central axis of the updraft, thus avoiding large errors that may occur by averaging variables across the entire updraft. Comparison of the model output with two 3D cloud model simulations proved to be ideal for utilization in the development of this model due to the small wind shear in these cases and to the significant difference in atmospheric stability in the soundings that were used.

Ridout, James A.↗

NASA NTRS1923

Tests on an airplane model, AEG D I of the Allgemeine Elektricitats Gesellschft, A-G, airplane construction section conducted at the Gottingen Model Testing Laboratory for Aerodynamics

Tests were carried out in the small wind tunnel of the Gottingen establishment on a complete model of the AEG D I airplane. The agreement between the model and the complete airplane applies particularly to the wings, which have ribs cut out of sheet metal and built up in exactly the same manner as in the actual airplane. Various series of tests were carried out with this model in which one or the other of the control surfaces were adjusted to various angles, while the others remained in their neutral positions. During the first three series of tests, the stabilizer was set at a positive angle of 3 degrees, 45' relative to the axis of the engine crankshaft, after which further tests at a 6 degree 30' we made. Finally, the model was tested with the tail group removed. With the elevators set in the prescribed positions, the lift, the drag, and the moments about an axis passing through the center of gravity and perpendicular to the plane of symmetry were measured. All three sets of readings are given as absolute coefficients. Where one of the other control surfaces was deflected from its normal position, the moment produced by that adjustment of the surface was also measured.

Munk, Max↗

NASA NTRS1924

Tests on a model of the D.F.W. airplane T-29 of the "Deutsche Flugzeug derke" (German airplane works)

Experiments similar to those carried out with the A.E.G (Allgemeine Elektrizitats-Gesellschaft) were made in the small wind tunnel of the Gottingen laboratory on a model of the D.F.W. airplane T-29. Three series of tests were carried out on the model with a velocity head (or dynamic pressure) of 5 kg/sq m (1.02 lb/sq ft), during which one of the movable surfaces was deflected at various angles, while both the others were retained in their central positions. Of special interest among the results of the tests is the different run of the elevating moments. The curves for the A.E.G. model, rising to the right, denote stability with the elevator locked, while the slight inclination to the left with the D.F.W model denotes a slight instability. For the maximum C(sub L) values, the stability of A.E.G. model continues to increase and the instability of the D.F.W. model is converted into stability. The rolling moments shown when the angular deflection of the ailerons is 0 degrees are due, in both series of tests, to the unequal distribution of the air velocity over the cross section of the wind tunnel, rather than to a lack of symmetry in the model.

Molthan, Wilhelm↗

NASA NTRS1931

Downwash measurements behind wings with detached float

This investigation, which was made in the small wind tunnel having a diameter of 1.2 m (3.94 feet), embraced three wing models, behind which, at various angles of attack between 0 and 60 degrees, the static pressure and the total pressure along vertical lines (perpendicular to the direction of the undisturbed wind and to the wing span) were measured. The location of these vertical lines are indicated in Figure 1. Moreover, the wing polars were determined by the customary three-component measurements. For testing the pressure field, a Pitot tube and a static probe, both of 2 mm (0.08 in.) in diameter, were mounted 40 mm (1.57 in.) apart on the end of a shaft 1 m (39.37 in.) long.

Petersohn, E↗

NASA NTRS1930

Velocity Distribution in the Boundary Layer of a Submerged Plate

This report deals with the measurement of the velocity distribution of the air in the velocity of a plate placed parallel to the air flow. The measurements took place in a small wind tunnel where the diameter of the entrance cone is 30 cm and the length of the free jet between the entrance and exit cones is about 2.5 m. The measurements were made in the free jet where the static pressure was constant, which was essential for the method of measurement used.

Hansen, M↗