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At least 217 records · Page 12

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NASA NTRS1981

Solar heating and hot water system installed at Arlington Raquetball Club, Arlington, Virginia

A solar space and water heating system is described. The solar energy system consists of 2,520 sq. ft. of flat plate solar collectors and a 4,000 gallon solar storage tank. The transfer medium in the forced closed loop is a nontoxic antifreeze solution (50 percent water, 50 percent propylene glycol). The service hot water system consists of a preheat coil (60 ft. of 1 1/4 in copper tubing) located in the upper third of the solar storage tank and a recirculation loop between the preheat coil and the existing electric water heaters. The space heating system consists of two separate water to air heat exchangers located in the ducts of the existing space heating/cooling systems. The heating water is supplied from the solar storage tank. Extracts from site files, specification references for solar modifications to existing building heating and hot water systems, and installation, operation and maintenance instructions are included.

Source record↗

NASA NTRS1982

Energy efficient engine: Turbine transition duct model technology report

The Low-Pressure Turbine Transition Duct Model Technology Program was directed toward substantiating the aerodynamic definition of a turbine transition duct for the Energy Efficient Engine. This effort was successful in demonstrating an aerodynamically viable compact duct geometry and the performance benefits associated with a low camber low-pressure turbine inlet guide vane. The transition duct design for the flight propulsion system was tested and the pressure loss goal of 0.7 percent was verified. Also, strut fairing pressure distributions, as well as wall pressure coefficients, were in close agreement with analytical predictions. Duct modifications for the integrated core/low spool were also evaluated. The total pressure loss was 1.59 percent. Although the increase in exit area in this design produced higher wall loadings, reflecting a more aggressive aerodynamic design, pressure profiles showed no evidence of flow separation. Overall, the results acquired have provided pertinent design and diagnostic information for the design of a turbine transition duct for both the flight propulsion system and the integrated core/low spool.

Leach, K.↗

NASA NTRS2003

High Temperature Fusion Reactor Cooling Using Brayton Cycle Based Partial Energy Conversion

For some future space power systems using high temperature nuclear heat sources most of the output energy will be used in other than electrical form, and only a fraction of the total thermal energy generated will need to be converted to electrical work. The paper describes the conceptual design of such a partial energy conversion system, consisting of a high temperature fusion reactor operating in series with a high temperature radiator and in parallel with dual closed cycle gas turbine (CCGT) power systems, also referred to as closed Brayton cycle (CBC) systems, which are supplied with a fraction of the reactor thermal energy for conversion to electric power. Most of the fusion reactor's output is in the form of charged plasma which is expanded through a magnetic nozzle of the interplanetary propulsion system. Reactor heat energy is ducted to the high temperature series radiator utilizing the electric power generated to drive a helium gas circulation fan. In addition to discussing the thermodynamic aspects of the system design the authors include a brief overview of the gas turbine and fan rotor-dynamics and proposed bearing support technology along with performance characteristics of the three phase AC electric power generator and fan drive motor.

Juhasz, Albert J.↗

NASA NTRS1978

Duct wall impedance control as an advanced concept for acoustic suppression enhancement

A systems concept procedure is described for the optimization of acoustic duct liner design for both uniform and multisegment types. The concept was implemented by the use of a double reverberant chamber flow duct facility coupled with sophisticated computer control and acoustic analysis systems. The optimization procedure for liner insertion loss was based on the concept of variable liner impedance produced by bias air flow through a multilayer, resonant cavity liner. A multiple microphone technique for in situ wall impedance measurements was used and successfully adapted to produce automated measurements for all liner configurations tested. The complete validation of the systems concept was prevented by the inability to optimize the insertion loss using bias flow induced wall impedance changes. This inability appeared to be a direct function of the presence of a higher order energy carrying modes which were not influenced significantly by the wall impedance changes.

Dean, P. D.↗

NASA NTRS1993

Active control of fan-generated plane wave noise

Subsonic propulsion systems for future aircraft may incorporate ultra-high bypass ratio ducted fan engines whose dominant noise source is the fan with blade passage frequency less than 1000 Hz. This low frequency combines with the requirement of a short nacelle to diminish the effectiveness of passive duct liners. Active noise control is seen as a viable method to augment the conventional passive treatments. An experiment to control ducted fan noise using a time domain active adaptive system is reported. The control sound source consists of loudspeakers arrayed around the fan duct. The error sensor location is in the fan duct. The purpose of this experiment is to demonstrate that the in-duct error sensor reduces the mode spillover in the far field, thereby increasing the efficiency of the control system. In this first series of tests, the fan is configured so that predominantly zero order circumferential waves are generated. The control system is found to reduce the blade passage frequency tone significantly in the acoustic far field when the mode orders of the noise source and of the control source are the same. The noise reduction is not as great when the mode orders are not the same even though the noise source modes are evanescent, but the control system converges stably and global noise reduction is demonstrated in the far field. Further experimentation is planned in which the performance of the system will be evaluated when higher order radial and spinning modes are generated.

Gerhold, Carl H.↗

NASA NTRS2007

Numerical Technique for Analyzing Rotating Rake Mode Measurements in a Duct With Passive Treatment and Shear Flow

A technique is presented for the analysis of measured data obtained from a rotating microphone rake system. The system is designed to measure the interaction modes of ducted fans. A Fourier analysis of the data from the rotating system results in a set of circumferential mode levels at each radial location of a microphone inside the duct. Radial basis functions are then least-squares fit to this data to obtain the radial mode amplitudes. For ducts with soft walls and mean flow, the radial basis functions must be numerically computed. The linear companion matrix method is used to obtain both the eigenvalues of interest, without an initial guess, and the radial basis functions. The governing equations allow for the mean flow to have a boundary layer at the wall. In addition, a nonlinear least-squares method is used to adjust the wall impedance to best fit the data in an attempt to use the rotating system as an in-duct wall impedance measurement tool. Simulated and measured data are used to show the effects of wall impedance and mean flow on the computed results.

Dahl, Milo D.↗

NASA NTRS2005

Performance of a Checkerboard Liner With Uncertain Impedances

The current fleet of large commercial aircraft has successfully achieved FAA noise certifications because of, in part, the successful application of uniform passive duct liner treatments to control engine system noise. One goal of NASA's engine system noise reduction program is to develop technologies to improve the sound absorbing properties of duct liner treatments so that they remain effective in modern turbo fan engines. One such technology being studied is checkerboard or periodic axially and circumferentially segmented liners. A preliminary assessment of the potential of this technology was conducted by applying uncertainties associated with manufacturing, installation, source structure, and tonal frequency to a liner developed using deterministic design methods and generating a measure of improvement with respect to a uniform liner subjected to the same uncertainties. Deterministic design and analysis of the candidate checkerboard liner showed that it obtains a 1.5 dB per duct aspect ratio improvement in liner attenuation over a similarly designed uniform liner. When uncertainties in liner impedances, source structure, and frequency are considered, the performance of the checkerboard liner drops off dramatically. The final results of this paper show that the candidate checkerboard liner has a less than 25 percent chance of outperforming the uniform liner when moderate levels of uncertainty are considered. It is important to note that this study did not include the effects of mean flow on liner performance and, more important to note, that as a gradient based optimization process was used to design the checkerboard liner, it is almost certain that a global optimal design was not found for the candidate checkerboard liner. Had it been possible to find a better deterministically performing checkerboard liner, the probability that this candidate liner would outperform the uniform liner would certainly have been higher.

Robinson, J. H.↗

NASA NTRS1973

Terminal shock position and restart control of a Mach 2.7, two-dimensional, twin duct mixed compression inlet

Experimental results of terminal shock and restart control system tests of a two-dimensional, twin-duct mixed compression inlet are presented. High-response (110-Hz bandwidth) overboard bypass doors were used, both as the variable to control shock position and as the means of disturbing the inlet airflow. An inherent instability in inlet shock position resulted in noisy feedback signals and thus restricted the terminal shock position control performance that was achieved. Proportional-plus-integral type controllers using either throat exit static pressure or shock position sensor feedback gave adequate low-frequency control. The inlet restart control system kept the terminal shock control loop closed throughout the unstart-restart transient. The capability to restart the inlet was non limited by the inlet instability.

Cole, G. L.↗

NASA NTRS1986

Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

The objective of this investigation was the experimental evaluation of bulk turbulence and boundary thickness influence on the secondary flow development in a square, 90 deg turning duct. A three dimensional laser velocimetry system was utilized to measure the mean and fluctuating components of velocity in the large curved duct facility. The three dimensional development of the viscous shear layers in the curved duct has a strong influence on the complete flow field. Since ducted three dimensional flows are found in many engineering applications, including gas turbine engines, and contain high turbulence levels and high wall heat transfer rates, they present a difficult challenge to computational fluid mechanics codes. Turbulence modeling remains one of constraints to CFD advance due to inadequate physical understanding and experimental definition of turbulent shear flows. The results of this investigation expand the curved duct data base to higher turbulence levels and thicker entrance boundary layers. The experimental results provide a challenging benchmark data base for computational fluid dynamics code development and validation. The variation of inlet bulk turbulence intensity provides additional information to aid in turbulence model evaluation.

Crawford, Roger A.↗

NASA NTRS1990

Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

Shohadaee, Ahmad A.↗

NASA NTRS1992

Advanced ramjet concepts program

Uniquely advantageous features, on both the performance and weight sides of the ledger, can be achieved through synergistic design integration of airbreathing and rocket technologies in the development of advanced orbital space transport propulsion systems of the combined cycle type. In the context of well understood advanced airbreathing and liquid rocket propulsion principles and practices, this precept of synergism is advanced mainly through six rather specific examples. These range from the detailed component level to the overall vehicle system level as follows: using jet compression; achieving a high area ratio rocket nozzle; ameliorating gas generator cycle rocket system deficiencies; using the in-duct special rocket thrust chamber assembly as the principal scramjet fuel injection operation; using the unstowed, covered fan as a duct closure for effecting high area ratio rocket mode operation; and creating a unique airbreathing rocket system via the onboard, cryogenic hydrogen induced air liquefaction process.

Leingang, J. L.↗

NASA NTRS1948

Ice Protection of Turbojet Engines by Inertia Separation of Water III : Annular Submerged Inlets

Aerodynamic and icing studies were conducted on a one-half-scale model of an annular submerged inlet for use with axial-flow turbojet engines. Pressure recoveries, screen radial-velocity profiles, circumferential mass-flow variations, and icing characteristics were determined at the compressor inlet. In order to be effective in maintaining water-free induction air, the inlet gap must be extremely small and ram-pressure recoveries consequently are low, the highest achieved being 65 percent at inlet-velocity ratio of 0.86. All inlets exhibited considerable screen icing. Severe mass-flow shifts occurred at angles of attack.

ICE PREVENTION AND REMOVAL - PROPULSION SYSTEMS↗

NASA NTRS1984

Uniformly spaced field-aligned ionization ducts

A number of interesting cases of combination mode ducted echoes for mid- and low-latitude regions are presented that show nearly uniformly spaced multiple combination mode traces on the ionograms in the frequency range above 1 MHz. These traces suggest that a parallel system of field-aligned ducts is present. Ray tracing studies are made to determine the structure that would explain the observations using the electron density profile derivable from the vertical trace and assuming field-aligned ducts. Spacing perpendicular to the ducts is found to be as much as 70 km. Some of these parallel duct structures are found to extend to the conjugate hemisphere, possibly to the F peak.

Gross, S. H.↗

NASA NTRS1977

MSFC hot air collectors. Phase 1: Test report

A development test program of 3 hot air flat plate solar collectors is described in detail. The pressure drop versus flow rate performance characteristics for these collectors, mounted in series, was determined under 14 different test conditions each of which was characterized by a unique combination of inlet air temperature and air flow rate. Characteristics of inlet, exit and transfer ducts of these collectors were also determined during this testing. The test results indicate that significant pressure drop occurs at air flow rates greater than 150 standard cubic feet per minute and this drop is not heavily dependent upon inlet air temperature; and inlet, exit and transfer duct characteristics differ sufficiently to suggest that system performance may be enhanced through careful design of each type of duct individually.

Losey, R.↗

NASA NTRS1972

A study of internal drag of small-scale ducts at Mach number 4

An experimental investigation was made to examine the applicability of methods used to determine internal drag of small ducts and to study some of the problems encountered in assessing momentum losses in such ducts. Test Mach numbers ranged from 3.7 to 4.4 at angles of attack of 0 and 5 degrees and at a constant Reynolds number of 4.3 million per foot. The configurations represented small ducts used to simulate external aerodynamics of air breathing propulsion systems and consisted of wing nacelle models of ducts with circular, square, and rectangular inlets and with a two-dimensional inlet.

Graham, L. A.↗

NASA NTRS1979

Reciprocity principle in duct acoustics

Various reciprocity relations in duct acoustics have been derived on the basis of the spatial reciprocity principle implied in Green's functions for linear waves. The derivation includes the reciprocity relations between mode conversion coefficients for reflection and transmission in nonuniform ducts, and the relation between the radiation of a mode from an arbitrarily terminated duct and the absorption of an externally incident plane wave by the duct. Such relations are well defined as long as the systems remain linear, regardless of acoustic properties of duct nonuniformities which cause the mode conversions.

Cho, Y. C.↗

NASA NTRS1979

Reciprocity principle in duct acoustics

Cho, Y.-C.↗

NASA NTRS1961

Stability and Control Characteristics of a Small-Scale Model of an Aerial Vehicle Supported by Two Ducted Fans

An investigation has been made to determine the stability and control characteristics in hovering and in forward flight of a free-flight model representing a type of vertical-take-off-and-landing aircraft which utilizes two fixed ducted fans as its sole source of lift and propulsion. The model, having fans 28 inches in diameter, was considered to be approximately one-third the size of a full-scale aircraft. Control moments for most of the hovering tests and all the forward-flight tests were provided by remotely controlled compressed-air jets at the sides and ends of the model. For one brief phase of the hovering investigation a system of vanes in the duct slipstreams was substituted for the jets as a means of roll control. During the forward-flight tests, the model was flown with both the tandem and side-by-side duct arrangements. In hovering the model exhibited strongly divergent oscillations about the pitch and roll axes. The pitching oscillation of the tandem configuration was of a fairly long period and was not particularly difficult to control; the rolling oscillation, however, was of a relatively short period and was extremely difficult to control. Both oscillations could be completely eliminated by the addition of a sufficient amount of artificial damping. The control moments produced by the vane-type roll control system were weak and were accompanied by a side force of appreciable magnitude and undesirable direction. In forward flight the model required an undesirably large nose-down tilt angle for equilibrium at any appreciable speed. A vane was placed transversely in the slipstream of the forward duct of the tandem configuration in an attempt to reduce this tilt angle. The vane was effective in reducing the tilt angle but apparently caused an increase in the power requirements and in the angle-of-attack instability. Without the vane, a forward speed of 30 knots (full scale) required a nose-down tilt angle of about 300. A powerful pitch control moment was required not only to maintain the trim attitude but also to 2 overcome the effects of instability with angle of attack. Less pitch control moment was required for the tandem configuration than for the side-by-side configuration at any given forward speed. The instability in roll increased with forward speed. No forward speeds in excess of about 20 knots (full scale) were achieved until the artificial damping in roll and the yaw control moment were increased appreciably above values which had proved satisfactory for hovering flight.

Parlett, Lysle P.↗