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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1949

On Wind Tunnel Tests and Computations Concerning the Problem of Shrouded Propellers

Results of measurements on a shrouded propeller are given. The propeller is designed for the high ratio of advance and high thrust loading. The effect of the shape of propeller and shroud upon the aerodynamic coefficients of the propulsion unit can be seen from the results. The highest efficiency measured is 0.71. The measurements permit the conclusion that the maximum efficiency can be essentially improved by shroud profiles of small chord and thickness. The largest static thrust factor of merit measured reaches according to Bendemann, a value of about zeta = 1.1. By the use of a nose split flap the static thrust for thin shroud profiles with small nose radius can be about doubled. In a separate section numerical investigations of the behavior of shrouded propellers for the ideal case and for the case with energy losses are carried out. The calculations are based on the assumption that the slipstream cross section depends solely on the shape of the shroud and not on the propeller loading. The reliability of this hypothesis is confirmed experimentally and by flow photographs for a shroud with small circulation. Calculation and test are also in good agreement concerning efficiency and static thrust factor of merit. The prospects of applicability for shrouded propellers and their essential advantages are discussed.

Kruger, W.↗
NASA NTRS1991

Numerical simulation of shrouded propellers

A numerical model was developed for the evaluation of the performance characteristics of a shrouded propeller. Using this model, a computational study was carried out to investigate the feasibility of improving the aerodynamic performance of a propeller by encasing it in a shroud. The propeller blade was modeled by a segmented bound vortex positioned along the span of the blade at its quarter-chord-line. The shroud was modeled by a number of discrete vortex rings. Due to the mutual dependence of shroud and propeller vortex strengths and the propeller vortex wake an iterative scheme was employed. Three shroud configurations were considered: a cylindrical and two conical shrouds. The computed performance of the shrouded propeller was compared with that of a free propeller of identical propeller geometry. The numerical results indicated that the cylindrical shroud outperformed the conical shroud configurations for the cases considered. Furthermore, when compared to the free propeller performance, the cylindrical shroud showed a considerable performance enhancement over the free propeller. However, the improvements were found to decrease with an increase in the advance ratio and to virtually diminish at advance ratios of about 2.5.

Afjeh, Abdollah A.↗
NASA NTRS1980

Aeroacoustic wind-tunnel tests of a light twin-boom general-aviation airplane with free or shrouded-pusher propellers

Tests were conducted in the Langley full-scale tunnel to determine the aerodynamic performance and acoustic characteristics of four different pusher-propeller configurations on a twin boom, general aviation airplane. The propellers included a 2-blade free propeller, two 3-blade shrouded propellers, and a 5-blade shrouded propeller. The tests were conducted for a range of airplane angles of attack from about 0 deg to 16 deg for test speeds from 0 to about 36 m/sec and for a range of propeller blade angles and rotation speeds. The free propeller provided the best aerodynamic propulsive performance. For forward flight conditions, the free propeller noise levels were lower than those of the shrouded propellers. In the static conditions the free propeller noise levels were as low as those for the shrouded propellers, except for the propeller in-plane noise where the shrouded propeller noise levels were lower.

Mclemore, H. C.↗
NASA NTRS2012

Concepts for a Shroud or Propellant Tank Derived Deep Space Habitat

Long duration human spaceflight missions beyond Low Earth Orbit will require much larger spacecraft than capsules such as the Russian Soyuz or American Orion Multi-Purpose Crew Vehicle. A concept spacecraft under development is the Deep Space Habitat, with volumes approaching that of space stations such as Skylab, Mir, and the International Space Station. This paper explores several concepts for Deep Space Habitats constructed from a launch vehicle shroud or propellant tank. It also recommends future research using mockups and prototypes to validate the size and crew station capabilities of such a habitat. Keywords: Exploration, space station, lunar outpost, NEA, habitat, long duration, deep space habitat, shroud, propellant tank.

Howard, Robert L.↗
NASA NTRS1980

Performance and noise of a low pressure ratio variable pitch fan designed for general aviation applications

A limited study has been conducted to establish the performance and noise characteristics of a low design tip speed (168 m/s, 550 ft/sec) low pressure ratio (1.04) variable pitch fan which was tested in the Langley 30 X 60 tunnel. This fan was designed for minimum noise when installed in the tail mount location of a twin engine aircraft which normally has both nose and tail mounted propulsors. Measurements showed the fan noise to be very close to predictions made during the design of the fan and extremely low in level (65 dBA at 1000 ft) with no acoustic treatment. This is about 8 dB lower than the unshrouded 2 blade propeller normally used in this installation. On the basis of tests conducted during this program, it appears that this level could be further reduced by 2 dBA if optimized acoustic treatments were installed in the fan duct. Even the best of the shrouded propellers tested previously were 7 dB higher in level than the Q-Fan without acoustic treatment. It was found that the cruise performance of this fan was within 5% of the predicted efficiency of 72%. Evaluation of the performance data indicated that disturbances in the inflow to the fan were the probable cause of the reduced performance.

Metzger, F. B.↗
NASA NTRS1979

Wind-tunnel investigation of an armed mini remotely piloted vehicle

A wind tunnel investigation of a full scale remotely piloted vehicle (RPV) armed with rocket launchers was conducted. The model had unacceptable longitudinal stability characteristics at negative angles of attack in the original design configuration. The addition of a pair of fins mounted in a V arrangement on the propeller shroud resulted in a configuration with acceptable longitudinal stability characteristics. The addition of wing mounted external stores to the modified configuration resulted in a slight reduction in the longitudinal stability. The lateral directional characteristics of the model were generally good, but the model had low directional stability at low angles of attack. Aerodynamic control power was very strong around all three axes.

Phelps, A. E., III↗
NASA NTRS1952

Concerning the flow about ring-shaped cowlings Part VIII : further measurements on annular profiles

The measurements of part V (reference 1) of this series of reports, which concerned comparatively long ring profiles, are supplemented by measurements on shorter rings as they are used for shrouded propellers and cowlings of ring-shaped radiators. Mass-flow coefficients and profile drags are given. Furthermore, it has to be determined how far the potential theory describes the flow phenomenon with sufficient accuracy and whether the present theory for the calculation of thin annular profile yields useful profile forms and is suitable for determination of the mass flow for thick profiles.

ENGINE COWLINGS, RING↗
NASA NTRS1948

Venturi Tube with Varying Mass Flow

Measurements on three tubes with flow regulated by suction at the trainling edge of the tube are described. It was possible to vary the mass of air flowing through the tube over a large range. Such tubes could be used for shrouded propellers.

Regenscheit, B.↗
NASA NTRSDate not supplied

Optimization of Variable Depth Acoustic Liners with Grazing Flow

Acoustic liners, typically used as a noise control treatment in the engine nacelles of conventional aircraft, are being considered for noise treatment in the proprotor ducts of a vertical takeoff and landing aircraft. This work considers a new optimization method to design an acoustic liner with variable depth cavities for broadband and low-frequency attenuation. This method, termed the direct optimization method, minimizes the radiated sound from a duct. In this paper, the new method is compared with an existing indirect method to design multiple variable depth acoustic liners. Acoustic impedances of liners designed using both methods are predicted using a semianalytical impedance model and impedance predictions for two designs are compared to experimental results acquired from grazing flow impedance testing. For the work presented here, liners designed using the indirect approach provide improved attenuation spectra over those designed using the direct approach but potential improvements to the performance of the direction optimization method are discussed.

Proprotor↗
NASA NTRS1992

Comparison of radiated noise from shrouded and unshrouded propellers

The ducted propeller in a free field is modeled using the finite element method. The generation, propagation, and radiation of sound from a ducted fan is described by the convened wave equation with volumetric body forces. Body forces are used to introduce the blade loading for rotating blades and stationary exit guide vanes. For an axisymmetric nacelle or shroud, the problem is formulated in cylindrical coordinates. For a specified angular harmonic, the angular coordinate is eliminated, resulting in a two-dimensional representation. A finite element discretization based on nine-node quadratic isoparametric elements is used.

Eversman, Walter↗
NASA NTRS2009

Inherently Ducted Propfans and Bi-Props

The terms inherently ducted propfan (IDP) and inherently ducted biprop (IDBP) denote members of a proposed class of propfan engines that would be quieter and would weigh less than do other propfan engines that generate equal amounts of thrust. The designs of these engines would be based on novel combinations of previously established aerodynamic-design concepts, including those of counter-rotating propfans, swept-back and swept-forward fixed wings, and ducted propfans. Heretofore, noise-reducing propfan designs have provided for installation of shrouds around the blades. A single propeller surrounded by such a shroud is denoted an advanced ducted propeller (ADP); a pair of counter-rotating propellers surrounded by such a shroud is denoted a counter-rotating integrated shrouded propeller (CRISP). In addition to adding weight, the shrouds engender additional undesired rotor/stator interactions and cascade effects, and contribute to susceptibility to choking. An IDP or IDBP would offer some shielding against outward propagation of noise, similar to shielding by a shroud, but without the weight and other undesired effects associated with shrouds. An IDP would include a pair of counter-rotating propellers. The blades of the upstream propeller would be swept back, while those of the downstream propeller would be swept forward (see figure). The downstream blades would have a geometric twist such that their forward-swept tips could act as winglets extending over the tips of the upstream blades. In principle, the resulting periodic coverage of the upstream-blade tips by the downstreamblade tips would suppress outward propagation of noise, as though a short noise-shielding duct were present. Furthermore, it is anticipated that an IDP would be less susceptible to some of the operational limitations of a CRISP during asymmetric flow conditions or reverse thrust operation.

Takallu, M. A.↗