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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Experimental investigation of a 0.15 scale model of a conformal variable-ramp inlet for the F-16 airplane

A 0.15 scale model of a proposed conformal variable-ramp inlet for the Multirole Fighter was tested from Mach 0.8 to 2.2 at a wide range of angles of attack and sideslip. Inlet ramp angle was varied to optimize ramp angle as a function of engine airflow, Mach number, angle of attack, and angle of sideslip. Several inlet configuration options were investigated to study their effects on inlet operation and to establish the final flight configuration. These variations were cowl sidewall cutback, cowl lip bluntness, boundary layer bleed, and first-ramp leading edge shape. Diagnostic and engine face instrumentation were used to evaluate inlet operation at various inlet stations and at the inlet/engine interface. Pressure recovery and stability of the inlet were satisfactory for the proposed application. On the basis of an engine stability audit of the worst-case instantaneous distortion patterns, no inlet/engine compatibility problems are expected for normal operations.

Hawkins, J. E.↗
NASA NTRS1980

Application of functional analysis to perturbation theory of differential equations

The deviation of the solution of the differential equation y' = f(t, y), y(O) = y sub O from the solution of the perturbed system z' = f(t, z) + g(t, z), z(O) = z sub O was investigated for the case where f and g are continuous functions on I x R sup n into R sup n, where I = (o, a) or I = (o, infinity). These functions are assumed to satisfy the Lipschitz condition in the variable z. The space Lip(I) of all such functions with suitable norms forms a Banach space. By introducing a suitable norm in the space of continuous functions C(I), introducing the problem can be reduced to an equivalent problem in terminology of operators in such spaces. A theorem on existence and uniqueness of the solution is presented by means of Banach space technique. Norm estimates on the rate of growth of such solutions are found. As a consequence, estimates of deviation of a solution due to perturbation are obtained. Continuity of the solution on the initial data and on the perturbation is established. A nonlinear perturbation of the harmonic oscillator is considered a perturbation of equations of the restricted three body problem linearized at libration point.

Bogdan, V. M.↗
NASA NTRS1980

A two-dimensional potential flow model for ground-induced effects on jet and fan inlets

A free-streamline potential flow model is developed for the flowfield external to a stationary jet or fan inlet in proximity to a ground plane. It is assumed that the flow is steady, incompressible, and irrotational. A two-dimensional flat plate geometry models the inlet configuration, and free streamline theory is used to avoid unrealistic infinite flow velocities at the lips of the inlet, and to account somewhat for flow separation. A water table experiment is used to verify the analytical results. The fact that the solutions are found to be limited to only a certain range of diameter-height ratios implies an overdetermination of the problem by free streamline theory. Also studied are the convective properties of small vortical disturbances superimposed on the ideal flow solution.

Newman, W. H.↗
NASA NTRS1980

A model for broadband jet noise amplification

A model is proposed for the change in turbulent structure of a round jet in the presence of an acoustic excitation. The excitation is assumed to trigger instability waves of a known initial amplitude at the jet exit. As these waves propagate downstream they extract energy from the mean flow and transfer it to the random turbulence. This results in an increase in the levels of the turbulence and a resulting increase in the radiated broadband noise. No calculations are presented for the noise radiation; however, an examination is made of the effect of excitation level and frequency on the jet flow. The numerical procedure allows for radial as well as axial variations in the averaged properties of jet to be calculated. The results indicate that the presence of a finite amplitude instability wave increases the spreading of the jet. It does not vary the characteristic radial shapes of both the axial mean velocity and the turbulent kinetic energy. An energy budget for the random turbulence shows that it is fed energy from the excited wave predominantly on each side of the jet lip line. This results in a broader radial shape for the turbulent kinetic energy.

Morris, P. J.↗
NASA NTRS1980

Subcutaneous electrode structure

A subcutaneous electrode structure suitable for a chronic implant and for taking a low noise electrocardiogram of an active animal, comprises a thin inflexible, smooth disc of stainless steel having a diameter as of 5 to 30 mm, which is sutured in place to the animal being monitored. The disc electrode includes a radially directed slot extending in from the periphery of the disc for approximately 1/3 of the diameter. Electrical connection is made to the disc by means of a flexible lead wire that extends longitudinally of the slot and is woven through apertures in the disc and held at the terminal end by means of a spot welded tab. Within the slot, an electrically insulative sleeve, such as silicone rubber, is placed over the wire. The wire with the sleeve mounted thereon is captured in the plane of the disc and within the slot by means of crimping tabs extending laterally of the slot and over the insulative wire. The marginal lip of the slot area is apertured and an electrically insulative potting material such as silicone rubber, is potted in place overlaying the wire slot region and through the apertures.

Lund, G. F.↗
NASA NTRS1980

Jet-diffuser Ejector - Attached Nozzle Design

Attached primary nozzles were developed to replace the detached nozzles of jet-diffuser ejectors. Slotted primary nozzles located at the inlet lip and injecting fluid normal to the thrust axis, and rotating the fluid into the thrust direction using the Coanda Effect were investigated. Experiments indicated excessive skin friction or momentum cancellation due to impingement of opposing jets resulted in performance degradation. This indicated a desirability for location and orientation of the injection point at positions removed from the immediate vicinity of the inlet surface, and at an acute angle with respect to the thrust axis. Various nozzle designs were tested over a range of positions and orientations. The problems of aircraft integration of the ejector, and internal and external nozzle losses were also considered and a geometry for the attached nozzles was selected. The effect of leaks, protrusions, and asymmetries in the ejector surfaces was examined. The results indicated a relative insensitivity to all surface irregularities, except for large protrusions at the throat of the ejector.

Alperin, M.↗
NASA NTRS1981

A Jet-diffuser ejector for a V/STOL fighter

A single ejector equipped with only one vector control jet and a diffuser flap was installed close to the leading edge of the strake of a one-fifth scale, semi-span model of the aircraft, without wing, canard, or tail surface. Tests of the system at a nozzle pressure ratio of 1.24 indicated a thrust augmentation of 1.92 and a thrust in the flight direction of about 12% of the total thrust under static conditions. An ejector stall occured at a ratio of tunnel dynamic pressure to nozzle gage pressure of about 0.008. Ejector stall speed can be delayed by using a boundary layer control jet at the front inlet lip of the ejector.

Alperin, M.↗
NASA NTRS1981

Additional testing of the inlets designed for a tandem fan V/STOL nacelle

The wind tunnel testing of a scale model of a tandem fan nacelle designed for a type (subsonic cruise) V/STOL aircraft configuration is discussed. The performance for the isolated front inlet and for the combined front and aft inlets is reported. Model variables include front and aft inlets with aft inlet variations of short and long aft inlet cowls, with a shaft simulator and diffuser vortex generators, cowl lip fillets, and nacelle strakes. Inlet pressure recovery, distortion, and inlet angle-to-attack separation limits were evaluated at tunnel velocity from 0 to 240 knots, angles-of-attack from -10 to +40 degrees and inlet flow rates corresponding to throat Mach number from 0.0 to 0.6. Combined nacelle pitch and yaw runs up to 30 deg. were also made.

Ybarra, A. H.↗
NASA NTRS1981

Organic Rankine cycle receiver development

The selected receiver concept is a direct-heated, once-through, monotube boiler operated at supercritical pressure. The cavity is formed by a cylindrical copper shell and backwall, with stainless steel tubing brazed to the outside surface. This core is surrounded by lightweight refractory insulation, load-bearing struts, and an outer case. The aperture plate is made of copper to provide long life by conduction and reradiation of heat away from the aperture lip. The receiver thermal efficiency is estimated to be 97 percent at rated conditions (energy transferred to toluene divided by energy incident on aperture opening). Development of the core manufacturing and corrosion protection methods is complete.

Haskins, H. J.↗
NASA NTRS1981

Turbomachinery noise studies of the AiResearch QCGAT engine with inflow control

The AiResearch Quiet Clean General Aviation Turbofan engine was tested on an outdoor test stand to compare the acoustic performance of two inflow control devices (ICD's) of similar design, and three inlet lips of different external shape. Only small performance differences were found. Far-field directivity patterns calculated by applicable existing analyses were compared with the measured tone and broadband patterns. For some of these comparisons, tests were made with an ICD to reduce rotor/inflow disturbance interaction noise, or with the acoustic suppression panels in the inlet or bypass duct covered with aluminum tape to determine hard wall acoustic performance. The comparisons showed that the analytical expressions used predict many directivity pattern features and trends, but can deviate in shape from the measured patterns under certain engine operating conditions. Some patterns showed lobes from modes attributable to rotor/engine strut interaction sources.

Mcardle, J. G.↗
NASA NTRS1981

Flow and far field acoustic amplification properties of heated and unheated jets

The interaction of an acoustic pulse with the experimentally determined mean flow field of a spreading jet is simulated numerically. The simulation is obtained through solving the Euler equations linearized about the spreading jet. The model reveals a small, sustained oscillation long after the original pulse has passed. This remnant is considered a continual shedding of vortices from the nozzle lip, together with the generation of acoustic ripples. IT is shown that the jet also acts as an amplifier of sound. This amplification is traced to the jet's stability characteristics. It is demonstrated that some of the observed differences in the spectra of heated and unheated jets can be attributed to differences in the stability characteristics of the jets.

Maestrello, L.↗
NASA NTRS1983

Growing Silicon Ribbon Horizontally

Solid ribbon of silicon pulled horizontally over lip of crucible. As heat leaves silicon by radiation, conduction, and convections, surface layer solidifies from liquid. Horizontal growth of ribbon offers several advantages over vertical growth. It is faster--possibly 1 to 2 centimeters per second-and is done without using drawing dies, source of contamination in vertical growth.

Zoutendyk, J. A.↗
NASA NTRS1981

Thrust modulation methods for a subsonic V/STOL aircraft

Low speed wind tunnel tests were conducted to assess four methods for attaining thrust modulation for V/STOL aircraft. The four methods were: (1) fan speed change, (2) fan nozzle exit area change, (3) variable pitch rotor (VPR) fan, and (4) variable inlet guide vanes (VIGV). The interrelationships between inlet and thrust modulation system were also investigated using a double slotted inlet and thick lip inlet. Results can be summarized as: (1) the VPR and VIGV systems were the most promising, (2) changes in blade angle to obtain changes in fan thrust have significant implications for the inlet, and (3) both systems attained required level of thrust with acceptable levels of fan blade stress.

Woollett, R. R.↗
NASA NTRS1981

The deflection of a jet by confining surfaces

Thrust vectoring can be provided by the turning of a jet exhaust by the presence of confining surfaces. This approach is analogous to the upper surface blowing (USB) concept. Mean velocities, velocity autocorrelations, and pressure-velocity correlations are measured. From the autocorrelation curves, the Taylor microscales and the integral length scales are calculated. Convection velocities are calculated from the velocity space-time correlations. Two different confining surfaces (one flat, one with large curvature) are placed adjacent to the lip of a circular nozzle, and the resultant effects on the flow field are determined. In addition, two velocity ratios (exit plane velocity to ambient stream velocity) are examined. The velocity measurements were made with a laser Doppler velocimeter in conjunction with a phase locked-loop processor. Pressure measurements were made using a 1/8th inch condensor type microphone.

Catalano, G. D.↗
NASA NTRS1981

Some aspects of calculating flows about three-dimensional subsonic inlets

Various three dimensional inlet models were calculated based on the potential flow model. Results are presented in the forms of surface static pressure, flow angularity, surface flow pattern, and inlet flow field. It is indicated that the extension of the lower lip can reduce the adverse pressure gradient and increase the flow separation bound.

Kao, H. C.↗
NASA NTRS1982

Effects of translational nonequilibrium on vacuum plume expansions

The plume flowfield of a helium vent nozzle exhausting into a vacuum is defined by two techniques: the method of characteristics and the direct-simulation Monte Carlo method. The method of characteristics is shown to severely underpredict gas static temperatures due to the assumption of translational equilibrium inherent in the continuum formulation. Mass flow per unit solid angle is shown to be accurately predicted for this flowfield by the method of characteristics until the flow angle approaches within 10 deg of the maximum Prandtl-Meyer expansion angle. Improved treatment of the noncontinuum flow within the nozzle (near the lip) is postulated to have minor effects on the accuracy of this continuum method in comparison with translational nonequilibrium in the external flowfield. Possible treatment of translational nonequilibrium by the method of characteristics is discussed.

Guernsey, C. S.↗
NASA NTRS1982

Utilizing numerical techniques in turbofan inlet acoustic suppressor design

Numerical theories in conjunction with previously published analytical results are used to augment current analytical theories in the acoustic design of a turbofan inlet nacelle. In particular, a finite element-integral theory is used to study the effect of the inlet lip radius on the far field radiation pattern and to determine the optimum impedance in an actual engine environment. For some single mode JT15D data, the numerical theory and experiment are found to be in a good agreement.

Baumeister, K. J.↗
NASA NTRS1982

Prediction of sound radiation from different practical jet engine inlets

Computer codes which were based upon a special integral representation of the external solutions of the Helmholtz equation were upgraded so that they would yield accurate results for the acoustic radiation patterns in the field surrounding an axisymmetric body for nondimensional wave numbers, based on duct radius, of up to twenty. The accuracy of these computer programs was checked by the use of the point source method for the generation of exact solutions and then by comparison with the results of other experimental and theoretical studies. These computer codes were used in a parametric study of the dependence of the radiated sound field on input modal distribution, wave number, and inlet lip shape. The results of this study show that: (1) as the wave number (i.e., cut off ratio) is increased for a given input modal distribution that the acoustic radiation peak moves towards the inlet centerline and becomes more compact (i.e., narrows); (2) as the input mode number is increased for a given cut off ratio the acoustic radiation peak moves away from the inlet centerline and becomes more compact.

Meyer, W. L.↗