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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 1,207 records · Page 67

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NASA NTRS1972

Influence of porous-wall thermal effectiveness on turbulent-boundary-layer heat transfer

In view of the interest in employing porous wall materials for which the wall thermal effectiveness is less than unity, the influence of the effectiveness on the convective heat-transfer coefficient is examined. A Couette-flow model of the turbulent boundary layer shows that the familiar expression for the Stanton number with mass transfer at the boundary is modified by a correction factor that accounts for the wall thermal effectiveness and the effectiveness of the film layer in protecting the surface from the hot gas stream. The correction term is found be of considerable importance for low values of blowing rate and wall thermal effectiveness.

Lecuyer, M. R.↗

NASA NTRS1972

Effective specific impulse of external nuclear pulse propulsion systems

An investigation of a simple self-similar flow model for an external nuclear pulse propulsion system indicates that to achieve the high effective specific impulse of such a system three principal factors are required. The are (1) attaining pulses of optimum energy, (2) attaining good propellant collimation, and (3) using an ablative material for the pusher surface which has high absorptivity for radiant energy at the propellant stagnation temperature.

Reynolds, T. W.↗

NASA NTRS1971

A note on multiple pure tone noise.

A theoretical investigation of multiple pure tone noise is presented. An analysis based on a two-dimensional inviscid flow model is developed to predict the generation and subsequent evolution of multiple pure tone noise from prescribed blade-to-blade nonuniformities in the rotor geometry. The results show that even small nonuniformities within manufacturing tolerances can be a significant source of multiple pure tone noise. Among the nonuniformities investigated, errors in blade spacing are less significant multiple pure tone noise sources than errors in blade stagger or blade contours.

Kurosaka, M.↗

NASA NTRS1972

Calculation of aerodynamic characteristics of STOL aircraft with externally-blown jet-augmented flaps.

Analytical methods to predict the interference between lifting surfaces and high-bypass-ratio turbofan engines are described. A three-dimensional nonplanar vortex-lattice lifting surface method is used to predict the characteristics of a wing with leading-edge slat and multiple slotted trailing-edge flaps including effects of externally induced velocity fields. A flow model of the wake of a high-bypass-ratio turbofan is described which is capable of predicting the induced velocity field both inside and outside the jet wake. These methods are combined to predict the longitudinal characteristics of several STOL transport models utilizing externally-blown flaps and comparisons with data are shown. The results indicate good agreement between experiment and theory for various configurations under a wide range of power conditions.

Mendenhall, M. R.↗

NASA NTRS1973

Prediction of overall and blade-element performance for axial-flow pump configurations

A method and a digital computer program for prediction of the distributions of fluid velocity and properties in axial flow pump configurations are described and evaluated. The method uses the blade-element flow model and an iterative numerical solution of the radial equilbrium and continuity conditions. Correlated experimental results are used to generate alternative methods for estimating blade-element turning and loss characteristics. Detailed descriptions of the computer program are included, with example input and typical computed results.

Serovy, G. K.↗

NASA NTRS1973

Flap noise prediction method for a powered lift system

A method is presented for estimating the noise generated by deflection of the engine exhaust for under-the-wing and over-the-wing versions of an externally blown flap configuration for powered lift. Correlation equations and curves are given for the overall sound pressure level and directivity and for spectra scaled to a high bypass 25,000-pound thrust size engine. Data are taken from TF34 engine tests and from large cold flow model tests. The correlations are empirical, and thus application of this prediction procedure is limited to geometrically similar configurations. Application of the method is illustrated by calculated sample footprints.

Clark, B.↗

NASA NTRS1972

Lee-side vortices on delta wings at hypersonic speeds.

A fluid-dynamic investigation was carried out to determine the cause of intense heating observed on the lee meridian of hypersonic delta wings and also to derive means for its suppression. Several experimental techniques were combined with analysis of extensive heat-transfer measurements at a freestream Mach number of six in a range of Reynolds number to acquire a general description of the lee-flow structure. With attached leading-edge flow on the delta wings, the dominant feature is a pair of embedded vortices on the lee meridian whose interaction with the boundary-layer is responsible for the observed local heating. On the basis of flow visualization results and heat-transfer correlations, a qualitative vortex flow model is proposed which differs essentially from the conventional inboard separation vortex model.

Rao, D. M.↗

NASA NTRS1974

Calculation of aerodynamic characteristics of STOL aircraft

Method predicts lift and pitching moment characteristics of STOL aircraft with externally-blown, jet-augmented wing-flap combinations using potential-flow approach which involves combination of two flow models. Method can accommodate multiple engines per wing panel and part-span flaps.

Dillenius, M. F. E.↗

NASA NTRS1974

Acoustic characteristics of externally blown flap systems with mixer nozzles

Noise tests were conducted on a large scale, cold flow model of an engine-under-the-wing externally blown flap lift augmentation system employing a mixer nozzle. The mixer nozzle was used to reduce the flap impingement velocity and, consequently, try to attenuate the additional noise caused by the interaction between the jet exhaust and the wing flap. Results from the mixer nozzle tests are summarized and compared with the results for a conical nozzle. The comparison showed that with the mixer nozzle, less noise was generated when the trailing flap was in a typical landing setting (e.g., 60 deg). However, for a takeoff flap setting (20 deg), there was little or no difference in the acoustic characteristics when either the mixer or conical nozzle was used.

Goodykoontz, J. H.↗

NASA NTRS1974

Externally blown flap noise research

The Lewis Research Center cold-flow model externally blown flap (EBF) noise research test program is summarized. Both engine under-the-wing and over-the-wing EBF wing section configurations were studied. Ten large scale and nineteen small scale EBF models were tested. A limited number of forward airspeed effect and flap noise suppression tests were also run. The key results and conclusions drawn from the flap noise tests are summarized and discussed.

Dorsch, R. G.↗

NASA NTRS1974

On the inlet vortex system

The flow field of a jet engine with an inlet vortex, which can pick up heavy debris from the ground and damage the engine, was simulated in a small water tunnel by means of the hydrogen bubble technique. It was found that the known engine inlet vortex is accompained by a vortex system, consisting of two inlet vortices (the ground based and the trailing one), secondary vortices, and ground vortices. Simulation of the ground effect by an inlet image proved that the inlet vortex feeds on free stream vorticity and can exist without the presence of a ground boundary layer. The structural form of the inlet vortex system was explained by a simple potential flow model, which showed the number, location, and the importance of the stagnation points. A retractable horizontal screen or an up-tilt of the engine is suggested as countermeasure against debris ingestion.

Bissinger, N. C.↗

NASA NTRS1973

Flap noise prediction method for a powered lift system

A method is presented for estimating the noise generated by deflection of the engine exhaust for under-the-wing and over-the-wing versions of an externally blown flap configuration for powered lift. Correlation equations and curves are given for the OASPL and directivity and for spectra scaled to a high bypass 25,000-pound thrust size engine. Data are taken from TF34 engine tests and from large cold flow model tests. The correlations are empirical, and thus application of this prediction procedure is limited to geometrically similar configurations. Application of the method is illustrated by calculated sample footprints.

Clark, B.↗

NASA NTRS1974

Acoustic characteristics of externally blown flap systems with mixer nozzles

Noise tests were conducted on a large-scale cold-flow model of an engine-under-the-wing externally blown flap lift augmentation system employing a mixer nozzle. The mixer nozzle was used to reduce the flap impingement velocity and, consequently, to try to attenuate the additional noise caused by the interaction between the jet exhaust and the wing flap. Results from the mixer nozzle tests are summarized and compared with the results for a conical nozzle. The comparison showed that, with the mixer nozzle, less noise was generated when the trailing flap was in a typical landing setting (e.g., 60 deg). However, for a takeoff flap setting (20 deg), there was little or no difference in the acoustic characteristics when either the mixer or conical nozzle was used.

Goodykoontz, J. H.↗

NASA NTRS1974

Externally blown flap noise research

Dorsch, R. G.↗

NASA NTRS1975

Numerical study of sound propagation in a jet flow

An improved computer oriented solution method for problems involving the propagation of sound through a nonuniform jet flow is developed. The method seeks to optimize the use of computer resources such as core storage space and central memory time. Complete formulation details are presented for a jet flow model consisting of a fixed point source on the jet center line in the potential core.

Padula, S. L.↗

NASA NTRS1975

A Three-Dimensional Solution of Flows over Wings with Leading-Edge Vortex Separation. Part 1: Engineering Document

A method of predicting forces, moments, and detailed surface pressures on thin, sharp-edged wings with leading-edge vortex separation in incompressible flow is presented. The method employs an inviscid flow model in which the wing and the rolled-up vortex sheets are represented by piecewise, continuous quadratic doublet sheet distributions. The Kutta condition is imposed on all wing edges. Computed results are compared with experimental data and with the predictions of the leading-edge suction analogy for a selected number of wing planforms over a wide range of angle of attack. These comparisons show the method to be very promising, capable of producing not only force predictions, but also accurate predictions of detailed surface pressure distributions, loads, and moments.

Brune, G. W.↗

NASA NTRS1975

A three-dimensional solution of flows over wings with leading-edge vortex separation

The application of a new, general, potential flow computational technique to the solution of the subsonic, three-dimensional flow over wings with leading-edge vortex separation is presented. The present method is capable of predicting forces, moments, and detailed surface pressures on thin, sharp-edged wings of rather arbitrary planform. The wing geometry is arbitrary in the sense that leading and trailing edges may be curved or kinked and the wing may have arbitrary camber and twist. The method employs an inviscid flow model in which the wing, the rolled-up vortex sheets, and the wake are represented by piecewise continuous quadratic doublet sheet distributions. The Kutta condition is imposed along all wing edges. Strengths of the doublet distributions as well as shape and position of the free fortex sheet spirals are computed in iterative fashion starting with an assumed initial sheet geometry. The method is verified by numerous computed results.

Weber, J. A.↗

NASA NTRS1976

Single stage, low noise, advanced technology fan. Volume 1: Aerodynamic design

The aerodynamic design for a half-scale fan vehicle, which would have application on an advanced transport aircraft, is described. The single stage advanced technology fan was designed to a pressure ratio of 1.8 at a tip speed of 503 m/sec 11,650 ft/sec). The fan and booster components are designed in a scale model flow size convenient for testing with existing facility and vehicle hardware. The design corrected flow per unit annulus area at the fan face is 215 kg/sec sq m (44.0 lb m/sec sq ft) with a hub-tip ratio of 0.38 at the leading edge of the fan rotor. This results in an inlet corrected airflow of 117.9 kg/sec (259.9 lb m/sec) for the selected rotor tip diameter if 90.37 cm (35.58 in.). The variable geometry inlet is designed utilizing a combination of high throat Mach number and acoustic treatment in the inlet diffuser for noise suppression (hybrid inlet). A variable fan exhaust nozzle was assumed in conjunction with the variable inlet throat area to limit the required area change of the inlet throat at approach and hence limit the overall diffusion and inlet length. The fan exit duct design was primarily influenced by acoustic requirements, including length of suppressor wall treatment; length, thickness and position on a duct splitter for additional suppressor treatment; and duct surface Mach numbers.

Sullivan, T. J.↗