SEARCH · Engineering Papers

Results for “ROTORS”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Structure and decay characteristics of turbulence in the near- and far-wake of a moderately loaded compressor rotor-blade

The wake of a turbomachinery rotor-blade is turbulent, highly three-dimensional, and nonisotropic with appreciable curvature in the trailing-edge and near-wake regions. The characteristics of the turbulence vary considerably with radius, blade loading, free-stream turbulence, Reynolds number, and the rotor-blade geometry. This paper is concerned with the turbulence properties of a moderately loaded compressor blade, particularly near the blade trailing-edge. The tangential variation of the axial, tangential and radial intensities and stresses across the wake, as well as their decay characteristics were measured with a tri-axial hot-wire probe in the rotor frame of reference. The decay of intensities and stresses were found to be very rapid in the trailing-edge and near-wake regions and slow in the far-wake region. The effects of inlet-guide-vane and the hub-wall boundary layers on the rotor wake turbulence spectra are also discussed. Similarity rules for the three components of intensity are also derived and presented in this paper.

Ravindranath, A.↗

NASA NTRS1981

Mean rotor wake characteristics of an aerodynamically loaded 0.5 m diameter fan

Mean rotor wake properties at several downstream distances behind the rotor of a loaded 1.2 pressure ratio fan were measured with a cross film anemometer in an anechoic wind tunnel. Mean wake characteristics in the midspan and near tip region were determined utilizing an ensemble averaging technique. The upwash and streamwise components of the velocity behind the rotor indicate a complex structure superimposed on the major velocity defects at a downstream spacing of 0.5 rotor chords. Spectral analysis indicates high levels of the second and fourth harmonics of the blade passage frequency in the midspan region while the blade passage frequency and its second and third harmonic are predominant in the tip region.

Shaw, L. M.↗

NASA NTRS1980

Sintered reaction bonded Si3N4 for the AGT 101 turbine rotor

The sintered reaction reaction bonded Si3N4 (SRBSN) process, with Y2O3 as a sintering aid, was selected for the fabrication of the AGT 101 turbine rotor. Experiments to determine the optimum Y2O3 composition of this system are discussed. The room temperature strength of the optimum material (RM-1) exceeds 700 MPa while the 1200 C strength exceeds 550 MPa. The slip casting fabrication technique employed for the AGT 101 simulated rotor is described. Rotors have been cast, nitrided and sintered. Densities exceeding 97% of theoretical (3.26 g/cc) have been obtained. Problems relating to sintering reproducibility, and the overall quality of the simulated rotors have been identified.

Mangels, J. A.↗

NASA NTRS1981

Freestream turbulence effects on the development of a rotor wake

The effect of freestream turbulence on the development of a three-dimensional wake of a compressor rotor blade was studied experimentally. The turbulence level at the inlet of a rotor was varied systematically using grids upstream of the rotor. The rotor wake was measured with inlet turbulence intensities of 0.5, 3, and 5%. The experimental results indicate that the maxium change in the mean velocity defect is 4% over the range of inlet turbulence levels employed, while the turbulence structure in the wake is altered more substantially. The freestream turbulence effect was also analyzed, numerically, using the modified Reynolds stress closure model. The comparison between numerical prediction and experimental data shows that the freestream turbulence effect can be represented successfully with the turbulence closure model employed in this paper.

Hah, C.↗

NASA NTRS1981

Full-scale wind-tunnel test of the aeroelastic stability of a bearingless main rotor

The rotor studied in the wind tunnel had previously been flight tested on a BO-105 helicopter. The investigation was conducted to determine the rotor's aeroelastic stability characteristics in hover and at airspeeds up to 143 knots. These characteristics are compared with those obtained from whirl-tower and flight tests and predictions from a digital computer simulation. It was found that the rotor was stable for all conditions tested. At constant tip speed, shaft angle, and airspeed, stability increases with blade collective pitch setting. No significant change in system damping occurred that was attributable to frequency coalescence between the rotor inplane regressing mode and the support modes. Stability levels determined in the wind tunnel were of the same magnitude and yielded the same trends as data obtained from whirl-tower and flight tests.

Warmbrodt, W.↗

NASA NTRS1982

Effect of seals on rotor systems

Seals can exert large forces on rotors. As an example, in turbopump ring seals film stiffness as high as 90 MN/m (500,000 lb/in) have been calculated. This stiffness is comparable to the stiffness of rotor support bearings; thus seals can play an important part in supporting and stabilizing rotor systems. The work done to determine forces generated in ring seals is reviewed. Working formulas are presented for seal stiffness and damping, and geometries to maximize stiffness are discussed. An example is described where a change in seal design stabilized a previously unstable rotor.

Fleming, D. P.↗

NASA NTRS1982

Method for predicting impulsive noise generated by wind turbine rotors

Large wind turbines can generate both broad band and impulsive noises. These noises can be controlled by proper choice of rotor design parameters such as rotor location with respect to the supporting tower, tower geometry and tip speed. A method was developed to calculate the impulsive noise generated when the wind turbine blade experiences air forces that are periodic functions of the rotational frequency. This phenomenon can occur when the blades operate in the wake of the support tower and the nonuniform velocity field near the ground due to wind shear. Results from this method were compared with measured sound spectra taken at locations of one to two rotor diameters from the DOE/NASA Mod-1 wind turbine. The calculated spectra generally agreed with the measured data in both the amplitude of the predominant harmonics and the roll of rate with frequency. Measured sound pressure levels far from the Mod-1 (15 rotor diameters), however, were higher than predicted. Simultaneous measurements in the near and far field indicated that the propagation effects could enhance the sound levels by more than 10 dB above that expected by spherical dispersion. These propagation effects are believed to be due to terrain and atmospheric characteristics of the Mod-1 site.

Viterna, L. A.↗

NASA NTRS1982

Performance testing of a main rotor system for a utility helicopter at 1/4 scale

Two rotor systems for the UH-1 helicopter were tested in hover and forward flight. The baseline system was a dynamically scaled model of the current rotor system, while the other system was designed for advanced performance. In hover out of ground effect, the advanced rotor system shows improvements up to 10 percent in the figure of merit and improvements in thrust up to 7 percent. In forward flight, the advanced rotor system demonstrated reductions in required torque throughout the range of conditions tested, with reductions up to 17 percent occurring at the higher advance ratios and higher lift values tested.

Berry, J. D.↗

NASA NTRS1982

Effect of rotor configuration on guyed tower and foundation designs and estimated costs for intermediate site horizontal axis wind turbines

Three designs of a guyed cylindrical tower and its foundation for an intermediate size horizontal axis wind turbine generator are discussed. The primary difference in the three designs is the configuration of the rotor. Two configurations are two-blade rotors with teetering hubs - one with full span pitchable blades, the other with fixed pitch blades. The third configuration is a three-bladed rotor with a rigid hub and fixed pitch blades. In all configurations the diameter of the rotor is 38 meters and the axis of rotation is 30.4 meters above grade, and the power output is 200 kW and 400 kW. For each configuration the design is based upon for the most severe loading condition either operating wind or hurricane conditions. The diameter of the tower is selected to be 1.5 meters (since it was determined that this would provide sufficient space for access ladders within the tower) with guy rods attached at 10.7 meters above grade. Completing a design requires selecting the required thicknesses of the various cylindrical segments, the number and diameter of the guy rods, the number and size of soil anchors, and the size of the central foundation. The lower natural frequencies of vibration are determined for each design to ensure that operation near resonance does not occur. Finally, a cost estimate is prepared for each design. A preliminary design and cost estimate of a cantilever tower (cylindrical and not guyed) and its foundation is also presented for each of the three configurations.

Frederick, G. R.↗

NASA NTRS1981

Dynamic Analysis of Darrieus Vertical Axis Wind Turbine Rotors

The dynamic response characteristics of the vertical axis wind turbine (VAWT) rotor are important factors governing the safety and fatigue life of VAWT systems. The principal problems are the determination of critical rotor speeds (resonances) and the assessment of forced vibration response amplitudes. The solution to these problems is complicated by centrifugal and Coriolis effects which can have substantial influence on rotor resonant frequencies and mode shapes. The primary tools now in use for rotor analysis are described and discussed. These tools include a lumped spring mass model (VAWTDYN) and also finite-element based approaches. The accuracy and completeness of current capabilities are also discussed.

Lobitz, D. W.↗

NASA NTRS1982

Aeroelastic analysis for helicopter rotors with blade appended pendulum vibration absorbers. Mathematical derivations and program user's manual

Mathematical development is presented for the expanded capabilities of the United Technologies Research Center (UTRC) G400 Rotor Aeroelastic Analysis. This expanded analysis, G400PA, simulates the dynamics of teetered rotors, blade pendulum vibration absorbers and the higher harmonic excitations resulting from prescribed vibratory hub motions and higher harmonic blade pitch control. Formulations are also presented for calculating the rotor impedance matrix appropriate to these higher harmonic blade excitations. This impedance matrix and the associated vibratory hub loads are intended as the rotor blade characteristics elements for use in the Simplified Coupled Rotor/Fuselage Vibration Analysis (SIMVIB). Sections are included presenting updates to the development of the original G400 theory, and material appropriate to the user of the G400PA computer program. This material includes: (1) a general descriptionof the tructuring of the G400PA FORTRAN coding, (2) a detaild description of the required input data and other useful information for successfully running the program, and (3) a detailed description of the output results.

Bielawa, R. L.↗

NASA NTRS1980

Selection of some rotor parameters to reduce pitch-roll coupling of helicopter flight dynamics

The results of a study conducted to investigate further a means of choosing primary rotor parameters to reduce the coupling of longitudinal and lateral flapping in hover and in forward flight are presented. The rotor parameters included - flapping hinge offset, flapping hinge restraint, pitch-flap coupling, and blade Lock number - are known to influence the agility, stability, and operational safety of helicopters. Effects of the nonuniform downwash model of White and Blake on the blade flapping motion are examined, and the theoretical calculation is then correlated with experimental test data. The condition for achieving perfect decoupling of the flapping response due to aircraft pitch and roll rates, which was previously obtained for a hovering rotor, is evaluated in forward flight. The results show that negligible coupling is achieved in forward flight; moreover, there is the additional benefit of a slight reduction in the coupling of the roll rate to coning. It is also indicated that the values of the rotor parameters chosen according to the decoupling condition are moderate and that the flapping motion is stable with the parameters chosen.

Chen, R. T. N.↗

NASA NTRS1982

Three-dimensional flow field in the tip region of a compressor rotor passage. II - Turbulence properties

The turbulence properties in the annulus wall region of an axial flow compressor rotor was measured using a triaxial, hot-wire probe rotating with the rotor. The flow was surveyed across the entire passage at five axial locations (leading edge, 1/4 chord, 1/2 chord, 3/4 chord, and the trailing edge location) and at six radial locations in a low-speed compressor rotor. The data derived include all three components of turbulence intensity and three components of turbulence stress. A comprehensive interpretation of the data with emphasis on features related to rotation, leakage flow, annulus wall boundary layer, and blade boundary layer interactions is included. All the components of turbulent intensities and stresses are found to be high in the leakage-flow mixing region. The radial component of intensities and stresses is found to be much higher than the corresponding streamwise components. The turbulent spectra clearly reveal the decay process of the inlet-guide-vane wake within the rotor passage.

Lakshminarayana, B.↗

NASA NTRS1982

Vibration limiting of rotors by feedback control

Experimental findings of a three mass rotor with four channels of feedback control are reported. The channels are independently controllable with force being proportional to the velocity and/or instantaneous displacement from equilibrium of the shaft at the noncontacting probe locations (arranged in the vertical and horizontal attitudes near the support bearings). The findings suggest that automatic feedback control of rotors is feasible for limiting certain vibration levels. Control of one end of a rotor does afford some predictable vibration limiting of the rotor at the other end.

Lewis, D. W.↗

NASA NTRS1982

Dynamic structural aeroelastic stability testing of the XV-15 tilt rotor research aircraft

For the past 20 years, a significant effort has been made to understand and predict the structural aeroelastic stability characteristics of the tilt rotor concept. Beginning with the rotor-pylon oscillation of the XV-3 aircraft, the problem was identified and then subjected to a series of theoretical studies, plus model and full-scale wind tunnel tests. From this data base, methods were developed to predict the structural aeroelastic stability characteristics of the XV-15 Tilt Rotor Research Aircraft. The predicted aeroelastic characteristics are examined in light of the major parameters effecting rotor-pylon-wing stability. Flight test techniques used to obtain XV-15 aeroelastic stability are described. Flight test results are summarized and compared to the predicted values. Wind tunnel results are compared to flight test results and correlated with predicted values.

Schroers, L. G.↗

NASA NTRS1983

A rotor technology assessment of the advancing blade concept

A rotor technology assessment of the Advancing Blade Concept (ABC) was conducted in support of a preliminary design study. The analytical methodology modifications and inputs, the correlation, and the results of the assessment are documented. The primary emphasis was on the high-speed forward flight performance of the rotor. The correlation data base included both the wind tunnel and the flight test results. An advanced ABC rotor design was examined; the suitability of the ABC for a particular mission was not considered. The objective of this technology assessment was to provide estimates of the performance potential of an advanced ABC rotor designed for high speed forward flight.

Pleasants, W. A.↗

NASA NTRS1983

A holographic interferometry technique for measuring transonic flow near a rotor blade

A technique that uses holographic interferometry to record the first interferograms of the flow near a hovering transonic rotor blade is presented. A pulsed ruby laser is used to record interferograms of a 2 ft diam field of view near a rotor tip operating at a tip Mach number of 0.90. Several interferograms, recorded along planes perpendicular to the rotor's tip path plane at various azimuth angles around the flow, are presented. These interferograms yield quantitative information about shock structure and location, flow separation, and radiated noise that will help helicopter researchers understand the complexities of the flow around high speed rotor blades and thus improve performance and reduce noise.

Kittleson, J. K.↗

NASA NTRS1983

Preliminary results of the first static calibration of the RSRA helicopter active-isolator rotor balance system

The helicopter version of the Rotor Systems Research Aircraft (RSRA) is designed to make simultaneous measurements of all rotor forces and moments in flight analogous to a wind tunnel balance. Loads are measured by a combination of load cells, strain gages, and hydropneumatic active isolators which use pressure gages to measure loads. Complete evaluation of system performance required calibration of the rotor force and moment measuring system when installed in the aircraft. Measurement system responses to rotor loads obtained during the first static calibration of the RSRA helicopter are plotted and discussed. Plots of the raw transducer data are included.

Acree, C. W., Jr.↗