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At least 595 records · Page 33

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NASA NTRS1985

Effects of inlet distortion on a static pressure probe mounted on the engine hub in an F-15 airplane

An inlet static pressure (PS2) probe was mounted on the hub of an F100 engine in an F-15 airplane. Flight test results showed that for low distortion conditions, the ratio of engine-face total pressure to static pressure agreed well with previous altitude facility data. Off-schedule operation of the inlet third ramp angle caused increased distortion of the inlet airflow during steady-state flight conditions. Data are shown for inlet third ramp excursions leading to engine stall. The relationships of inlet face total to static pressure ratio as a function of several distortion descriptors are also described.

Hughes, D. L.↗

NASA NTRS1985

Static investigation of several yaw vectoring concepts on nonaxisymmetric nozzles

A test has been conducted in the static test facility of the Langley 16-Foot Transonic Tunnel to determine the flow-turning capability and the effects on nozzle internal performance of several yaw vectoring concepts. Nonaxisymmetric convergent-divergent nozzles with throat areas simulating dry and afterburning power settings and single expansion ramp nozzles with a throat area simulating a dry power setting were modified for yaw thrust vectoring. Forward-thrust and pitch-vectored nozzle configurations were tested with each yaw vectoring concept. Four basic yaw vectoring concepts were investigated on the nonaxisymmetric convergent-divergent nozzles: (1) translating sidewall; (2) downstream (of throat) flaps; (3) upstream (of throat) port/flap; and (4) powered rudder. Selected combinations of the rudder with downstream flaps or upstream port/flap were also tested. A single yaw vectoring concept, post-exit flaps, was investigated on the single expansion ramp nozzles. All testing was conducted at static (no external flow) conditions and nozzle pressure ratios varied from 2.0 up to 10.0.

Mason, M. L.↗

NASA NTRS1985

Coupled low-energy - ring current plasma diffusion in the Jovian magnetosphere

The outwardly diffusing Iogenic plasma and the simultaneously inwardly diffusing ring current plasma in the Jovian magnetosphere are described using a coupled diffusion model which incorporates the effects of the pressure gradient of the ring current into the cross-L diffusion coefficient. The coupled diffusion coefficient is derived by calculating the total energy available to drive the diffusion process. The condition is imposed that the diffusion coefficient takes on a local minimum value at some point in the region L = 7-8, at which point the gradient of the Io plasma density is specified as ramp value given by Siscoe et al. (1981). The hypothesis that the pressure gradient of the ring current causes the diminution of radial plasma transport is tested, and solution profiles for the Iogenic and ring current plasma densities are obtained which imply that the Io plasma ramp is caused by a high-density, low-energy component of the ring current hitherto unobserved directly.

Summers, D.↗

NASA NTRS1985

Urban, Forest, and Agricultural AIS Data: Fine Spectral Structure

Spectra acquired by the Airborne Imaging Spectrometer (AIS) near Lafayette, IN, Ely, MN, and over the Stanford University campus, CA were analyzed for fine spectral structure using two techniques: the ratio of radiance of a ground target to the radiance of a standard and also the correlation coefficient of radiances at adjacent wavelengths. The results show ramp like features in the ratios. These features are due to the biochemical composition of the leaf and to the optical scattering properties of its cuticle. The size and shape of the ramps vary with ground cover.

Vanderbilt, V. C.↗

NASA NTRS1986

Effect of emerging technology on a convertible, business/interceptor, supersonic-cruise jet

This study was initiated to assess the feasibility of an eight-passenger, supersonic-cruise long range business jet aircraft that could be converted into a military missile carrying interceptor. The baseline passenger version has a flight crew of two with cabin space for four rows of two passenger seats plus baggage and lavatory room in the aft cabin. The ramp weight is 61,600 pounds with an internal fuel capacity of 30,904 pounds. Utilizing an improved version of a current technology low-bypass ratio turbofan engine, range is 3,622 nautical miles at Mach 2.0 cruise and standard day operating conditions. Balanced field takeoff distance is 6,600 feet and landing distance is 5,170 feet at 44,737 pounds. The passenger section from aft of the flight crew station to the aft pressure bulkhead in the cabin was modified for the interceptor version. Bomb bay type doors were added and volume is sufficient for four advanced air-to-air missiles mounted on a rotary launcher. Missile volume was based on a Phoenix type missile with a weight of 910 pounds per missile for a total payload weight of 3,640 pounds. Structural and equipment weights were adjusted and result in a ramp weight of 63,246 pounds with a fuel load of 30,938 pounds. Based on a typical intercept mission flight profile, the resulting radius is 1,609 nautical miles at a cruise Mach number of 2.0.

Beissner, F. L., Jr.↗

NASA NTRS1987

The response of a compressible turbulent boundary layer to short regions of concave surface curvature

An experimental investigation of the supersonic flow of a boundary layer over short regions of concave surface curvature, using radii of curvature equivalent to 10 and 50 (models I and II, respectively) initial boundary layer thicknesses and 8-deg turning angle, notes that the boundary layer experienced a strong adverse pressure gradient as the boundary layer passed through the curved region. Attention is given to the mean and turbulent field for each flow, with comparisons of results to those for an 8-deg ramp. In the ramp and model I, turbulence levels increased significantly, together with structural parameters; in model II, despite an increase in turbulence levels, structural parameters remained essentially unchanged. The former results suggest that the perturbation is rapid, and describable in terms of total rather than local strains.

Jayaram, Mohan↗

NASA NTRS1988

Generation, saturation, and convection of electrostatic waves in Jupiter's shock foot

In this paper, a model is developed for the analysis of the electrostatic waves produced in the shock foot at Jupiter. It is shown that an ion beam instability involving the ions reflected at the shock ramp and the incoming solar-wind electrons produces waves at the observed frequencies and that saturation via orbit diffusion limits the waves to amplitudes near to what is observed. Results from a two-dimensional model of the reflected beam in the foot indicate that the waves propagate against the solar wind away from the shock ramp and are amplified up to their saturation amplitudes. The saturation results, combined with the electron temperature profile due to wave-particle interactions predicted by quasi-linear theory, reproduce a wave amplitude profile for the shock foot that is in reasonable agreement with the observations.

Moses, S. L.↗

NASA NTRS1988

Cracking of a layered medium on an elastic foundation under thermal shock

The cladded pressure vessel under thermal shock conditions which is simulated by using two simpler models was studied. The first model (Model 1) assumes that, if the crack size is very small compared to the vessel thickness, the problem can be treated as a semi-infinite elastic medium bonded to a very thin layer of different material. However, if the crack size is of the same order as the vessel thickness, the curvature effects may not be negligible. In this case it is assumed that the relatively thin walled hollow cylinder with cladding can be treated as a composite beam on an elastic foundation (Model 2). In both models, the effect of surface cooling rate is studied by assuming the temperature boundary condition to be a ramp function. The calculated results include the transient temperature, thermal stresses in the uncracked medium and stress intensity factors which are presented as a function of time, and the duration of cooling ramp. The stress intensity factors are also presented as a function of the size and the location of the crack. The problem is solved for two bonded materials of different thermal and mechanical properties. The mathematical formulation results in two singular integral equations which are solved numerically. The results are given for two material pairs, namely an austenitic steel layer welded on a ferritic steel substrate, and a ceramic coating on ferritic steel. In the case of the yielded clad, the stress intensity factors for a crack under the clad are determined by using a plastic strip model and are compared with elastic clad results.

Rizk, Abd El-Fattah A.↗

NASA NTRS1988

Cracking of coated materials under transient thermal stresses

The crack problem for a relatively thin layer bonded to a very thick substrate under thermal shock conditions is considered. The effect of surface cooling rate is studied by assuming the temperature boundary condition to be a ramp function. Among the crack geometries considered are the edge crack in the coating layer, the broken layer, the edge crack going through the interface, the undercoat crack in the substrate and the embedded crack crossing the interface. The primary calculated quantity is the stress intensity factor at various singular points and the main variables are the relative sizes and locations of cracks, the time, and the duration of the cooling ramp. The problem is solved and rather extensive results are given for two material pairs, namely a stainless steel layer welded on a ferritic medium and a ceramic coating on a steel substrate.

Rizk, A. A.↗

NASA NTRS1989

Evaluation of parallel injector configurations for supersonic combustion

Techniques for the enhancement of mixing in a scramjet combustor are presently investigated experimentally with wall-mounted parallel injector ramps that are speculated to prove useful at high speeds in the extraction of thrust from engine- or airframe-coolant hydrogen. The injector ramps were designed to generate a reflected shock wave from the duct top wall which will pass just downstream of the fuel injectors' barrel shock; fuel injector Mach number is 1.7, in virtue of which an underexpanded fuel flow is generated. Shadowgraph and UV-TV flow visualizations were conducted for three duct configurations.

Northam, G. Burton↗

NASA NTRS1989

Observation of organized structure in turbulent flow within and above a forest canopy

Data obtained with seven triaxial sonic anemometer/thermometers and three Lyman-alpha hygrometers at an experimental site in Ontario, Canada reveal the coherent occurrence of ramp patterns of temperature and humidity at several levels within and above the deciduous forest considered. The ramps appear most clearly in the middle and upper portion of the forest, and near the top of the forest they are composed of a weak ejecting motion transporting warm and/or moist air out of the forest, followed by strong sweeps of cool and/or dry air penetrating into the canopy. In the middle and upper parts of the canopy, the sweeps are found to conduct a large proportion of the overall transfer between the forest and the lower atmosphere, with a lesser contribution from ejections.

Gao, W.↗

NASA NTRS1989

LOX/Hydrocarbon Combustion Instability Investigation

The LOX/Hydrocarbon Combustion Instability Investigation Program was structured to determine if the use of light hydrocarbon combustion fuels with liquid oxygen (LOX) produces combustion performance and stability behavior similar to the LOX/hydrogen propellant combination. In particular methane was investigated to determine if that fuel can be rated for combustion instability using the same techniques as previously used for LOX/hydrogen. These techniques included fuel temperature ramping and stability bomb tests. The hot fire program probed the combustion behavior of methane from ambient to subambient temperatures. Very interesting results were obtained from this program that have potential importance to future LOX/methane development programs. A very thorough and carefully reasoned documentation of the experimental data obtained is contained. The hot fire test logic and the associated tests are discussed. Subscale performance and stability rating testing was accomplished using 40,000 lb. thrust class hardware. Stability rating tests used both bombs and fuel temperature ramping techniques. The test program was successful in generating data for the evaluation of the methane stability characteristics relative to hydrogen and to anchor stability models. Data correlations, performance analysis, stability analyses, and key stability margin enhancement parameters are discussed.

Jensen, R. J.↗

NASA NTRS1990

An upwind-biased, point-implicit relaxation algorithm for viscous, compressible perfect-gas flows

An upwind-biased, point-implicit relaxation algorithm for obtaining the numerical solution to the governing equations for three-dimensional, viscous, compressible, perfect-gas flows is described. The algorithm is derived using a finite-volume formulation in which the inviscid components of flux across cell walls are described with Roe's averaging and Harten's entropy fix with second-order corrections based on Yee's Symmetric Total Variation Diminishing scheme. Viscous terms are discretized using central differences. The relaxation strategy is well suited for computers employing either vector or parallel architectures. It is also well suited to the numerical solution of the governing equations on unstructured grids. Because of the point-implicit relaxation strategy, the algorithm remains stable at large Courant numbers without the necessity of solving large, block tri-diagonal systems. Convergence rates and grid refinement studies are conducted for Mach 5 flow through an inlet with a 10 deg compression ramp and Mach 14 flow over a 15 deg ramp. Predictions for pressure distributions, surface heating, and aerodynamics coefficients compare well with experiment data for Mach 10 flow over a blunt body.

Gnoffo, Peter A.↗

NASA NTRS1989

Dynamic response for thermal control and measurement and fast radiation thermometry

A preliminary evaluation was made by ORNL of a two-color ratio pyrometer (TCRP) for temperature control in the Modular Electromagnetic Levitation (MEL) experiment. A discussion was presented by Eric Spjut at the 1987 NASA Non-Contact Temperature Measurement Workshop (NASA Conf. Publ. 2503, pp. 182-213) in which he described the non-linear characteristics of the time response of TCPs. Researchers replicated his model and results and note that the non-linear response behavior is minimized for small temperature steps at high temperatures. They then used the predicted response in a model for a proportional or integral feedback controller and predicted the control characteristics for heating and cooling a 5-mm diameter sphere of niobium at high (1500 to 2750 K) temperatures. The analysis shows that for a slow (25-ms) time response for a commercial RCRP, overshoots of several hundred kelvins will result from a 100-K decrease in the setpoint, and temperature tracking errors of 14 to 45 K will occur for control temperature ramps of 1000K/s. For a fast (greater than 0.1 ms) time response, the overshoot and ramp response errors are largely eliminated.

Shepard, R. L.↗

NASA NTRS1990

On the use of external burning to reduce aerospace vehicle transonic drag

The external combustion of hydrogen to reduce the transonic drag of aerospace vehicles is currently being investigated. A preliminary analysis based on a constant pressure control volume is discussed. Results indicate that the specific impulse of the external burning process rivals that of a turbojet and depends on the severity of the initial base drag as well as on the Mach flight number and the equivalence ratio. A test program was conducted to investigate hydrogen-air flame stability at the conditions of interest and to demonstrate drag reduction on a simple expansion ramp. Initial test results are presented and compared with the control-volume analysis. The expansion ramp surface pressure coefficient showed little variation with fuel pressure and altitude, in disagreement with the analysis. Flame stability results were encouraging and indicate that stable combustion is possible over an adequate range of conditions. Facility interference and chemical kinetics phenomena that make interpretation of subscale ground test data difficult are discussed.

Trefny, Charles J.↗

NASA NTRS1988

Design of a rotary stepped auger for a lunar environment

A lunar outpost will have need for deep drilling operations for both explorative and practical purposes. As in any drilling operation, the cuttings must be cleared from the hole. The hard vacuum of the lunar environment renders conventional flushing methods of cutting removal unfeasible, and requires a new system of removal. A rotary stepped auger (RSA) is a simple mechanical method of removing dry cuttings from a deep hole, and is ideally suited to the lunar environment. The RSA consists of a helical auger with stepped ramps which allow cuttings to slide up the helix, but will prevent them from sliding back down. The auger is driven in a pulsed manner by applying a periodic function of acceleration to the auger shaft. These pulses will compel the cuttings to slide up the auger's helix while the stepped ramps prevent the cuttings from backsliding while the auger accelerates. A mathematical model of the RSA was developed and experimentally evaluated. The math model produced a good baseline design, but the experimental model required some tuning to account for the approximations made in the math model. This design is suited for lunar drilling because it is mechanically simple, integral to the drill string, requires no fluids, is suited to the dry soil, and has relatively low weight and power requirements.

Dardet, Eduardo↗

NASA NTRS1989

First measurements of plasma waves near Mars

Preliminary results from electric field measurements in the environment of Mars using the plasma-wave system on board Phobos 2 are reported. Electron-plasma oscillations observed upstream of the bow shock correspond to a solar-wind density of 2/cu cm. The shock-foot boundary was crossed up to three times on each orbit. The shock ramp was detected at altitudes between 0.45 and 0.75 Mars radii R(M) above the planetary surface. The density increased by about a factor of two at the ramp. The shock position, although variable, seems to be consistent with previous measurements. The downstream magnetosheath contained broadband electric-field noise below the plasma frequency. The boundary of th obstacle, or plasmapause, was crossed at altitudes of the order of 0.28 R(M); the cold plasma density was highly variable within the planetopause and reached the unexpected value of 700/cu cm on the third orbit, at 0.25 R(M) altitude. Bursts of waves with frequencies below the electron cyclotron frequency occur within the planetopause.

Grard, R.↗

NASA NTRS1990

Supersonic flameholding by attached oblique shock waves

The object of this investigation was to explore various regimes of shock-induced combustion that may occur as a result of supersonic flow of a reactive gas mixture past a simple compression ramp or wedge. Attention was confined to combinations of wedge angles, fuel-air mixture ratios and freestream velocities that permit the resulting oblique shock or oblique detonation wave to remain attached. Computational fluid dynamic (CFD) simulations, both inviscid and viscous, were performed and analyzed in order to investigate two modes of compression ramp flameholding; namely, complete oblique detonation wave (ODW) and shock-induced combustion. In addition, the possibility of flame persistence or hysteresis was explored. It was preliminarily concluded that inclusion of viscous effects may be essential to accurately predict the occurrence of the various flameholding modes.

Fort, James A.↗