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At least 1,405 records · Page 78

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NASA NTRS1937

Static Thrust Analysis of the Lifting Airscrew

This report presents the results of a combined theoretical and experimental investigation conducted at the Georgia School of Technology on the static thrust of the lifting air screw of the type used in modern autogiros and helicopters. The theoretical part of this study is based on Glauert's analysis but certain modifications are made that further clarify and simplify the problem. Of these changes the elimination of the solidity as an independent parameter is the most important. The experimental data were obtained from tests on four rotor models of two, four, and five blades and, in general, agree quite well with the theoretical calculations. The theory indicates a method of evaluating scale effects on lifting air screws, and these corrections have been applied to the model results to derive general full-scale static thrust, torque, and figure-of-merit curves for constant-chord, constant-incidence rotors. Convenient charts are included that enable hovering flight performance to be calculated rapidly.

Knight, Montgomery↗

NASA NTRS1998

Calculation of Multistage Turbomachinery Using Steady Characteristic Boundary Conditions

A multiblock Navier-Stokes analysis code for turbomachinery has been modified to allow analysis of multistage turbomachines. A steady averaging-plane approach was used to pass information between blade rows. Characteristic boundary conditions written in terms of perturbations about the mean flow from the neighboring blade row were used to allow close spacing between the blade rows without forcing the flow to be axisymmetric. In this report the multiblock code is described briefly and the characteristic boundary conditions and the averaging-plane implementation are described in detail. Two approaches for averaging the flow properties are also described. A two-dimensional turbine stator case was used to compare the characteristic boundary conditions with standard axisymmetric boundary conditions. Differences were apparent but small in this low-speed case. The two-stage fuel turbine used on the space shuttle main engines was then analyzed using a three-dimensional averaging-plane approach. Computed surface pressure distributions on the stator blades and endwalls and computed distributions of blade surface heat transfer coefficient on three blades showed very good agreement with experimental data from two tests.

Chima, Rodrick V.↗

DOE OSTI2021

A Heterogeneous System for Eagle Detection, Deterrent, and Wildlife Collision Detection for Wind Turbines (Final Technical Report)

This report summarizes the design, implementation, and test of an integrated system for automated detection and deterrence of eagles, with included wind turbine blade strike detection and imaging functionality. A machine learning approach was used in conjunction with a 360° camera system for automated detection and classification of golden eagles. This was developed using footage obtained from trained golden eagles and other raptors, in collaboration with wildlife biologists and professional bird handlers. Oregon State University developed a visual deterrent system, which uses inflatable anthropomorphic sculptures with random, kinetic motion to deter eagles, and conducted limited field testing on live eagles; the deterrent can be triggered by the visual detection of eagles using the vision system. Finally, a multi-sensor module was developed that is mounted at the turbine blade root. This module measures vibration and other motions to detect blade strikes, and an integrated on-blade camera captures an image of any impacting objects. Long-term, this blade strike detection system is intended to support an automatic monitoring and certification system for the eagle detection and deterent system. Independent field testing of each system component is described. Testing of the integrated system on an operational wind turbine was conducted across three separate field tests. This includes multi-day fields tests on a General Electric 1.5MW wind turbine at the National Renewable Energy Laboratory (NREL) National Wind Technology Center (NWTC) in Boulder, CO in October 2018 and July 2019; installation procedures, test procedures, and a summary of collected data are presented. A third multi-day on-turbine field test is also presented, which was performed using a General Electric 1.5MW wind turbine at the North American Wind Research and Training Center (NAWRTC) at Mesalands Community College, Tucumcari, NM in April 2019. Across these field tests, the vision system was demonstrated using unmanned aerial vehicles (UAV), and the eagle classification algorithm was not tested; the visual deterrent system was demonstrated, including automatic, remote deployment following surrogate visual detections; and, multi-sensor on-blade data was recorded across multiple wind turbine operational conditions and through more than 100 surrogate blade strikes using soft projectiles, including the successful demonstration of automatic image capture of striking objects. This data set was also used for offline development and validation of enhanced collision detection algorithms. As summarized in this report, the development and field validation of an integrated detection, deterrent, and blade collision detection system represents a critical proof of concept for future technology development of related detection and deterrent technologies, where both deterrent as well as collision detection recording devices are needed for future siting, monitoring, and operation of wind turbine installations, both onshore and offshore.

17 WIND ENERGY↗

DOE OSTI2024

Computational Study of Additively Manufactured Internally Cooled Airfoils for Industrial Gas Turbine Applications

Internal cooling features such as pin-fins, impingement jets, and rib-turbulators are necessary to keep turbine components cool, but if sufficiently advanced can potentially also eliminate the need for film cooling on turbine blades particularly in industrial gas turbines where temperatures are not extreme. Furthermore, by leveraging additive manufacturing, other advanced designs such as lattice and incremental impingement configurations are possible and have recently been experimentally tested. While the performance of such configurations has been quantified through means of overall cooling effectiveness, it is not as clear why certain designs were better than others, or what the mechanisms were behind the observed external cooling patterns. The purpose of this study was to computationally analyze different advanced turbine blade internal cooling designs previously tested by the National Energy Technology Laboratory.

CFD↗

NASA NTRS1977

Design and performance of energy efficient propellers for Mach 0.8 cruise

The increased emphasis on fuel conservation in the world has stimulated a series of studies of both conventional and unconventional propulsion systems for commercial aircraft. Preliminary results from these studies indicate that a fuel saving of 14 to 40 percent may be realized by the use of an advanced high-speed turboprop. This turboprop must be capable of high efficiency at Mach 0.8 cruise above 9.144 km altitude if it is to compete with turbofan powered commercial aircraft. Several advanced aerodynamic concepts were investigated in recent wind tunnel tests under NASA sponsorship on two propeller models. These concepts included aerodynamically integrated propeller/nacelles, area ruling, blade sweep, reduced blade thickness and power (disk) loadings several times higher than conventional designs. The aerodynamic design methodology for these models is discussed. In addition, some of the preliminary test results are presented which indicate that propeller net efficiencies near 80 percent were obtained for high disk loading propellers operating at Mach 0.8.

Mikkelson, D. C.↗

NASA NTRS1986

An experimental investigation of the structural dynamics of a torsionally soft rotor in vacuum

An extensive data base of structural dynamic characteristics has been generated from an experimental program conducted on a torsionally soft two-bladed model helicopter rotor system. Measurements of vibratory strains for five modes of vibration were made at twenty-one locations on the two blades at speeds varying from 0 to 1000 RPM and for several combinations of precone, droop and flexure stiffness. Tests were conducted in vacuum under carefully controlled conditions using a unique excitation device with a system of piezoelectric crystals bonded to the blade surface near the root. Frequencies, strain mode shapes and dampings are extracted from the time histories and can be used to validate structural dynamics codes. The dynamics of the system are such that there is a clear tendency for the first torsion and second flap modes to couple within the speed range considered. Strain mode shapes vary significantly with speed and configuration. This feature is important in the calcualtion of aeroelastic instabilities. The tension axis tests confirmed that the modulus-weighted centroid for the nonhomogeneous airfoil is slightly off the mass centroid and validated previous static tests done to determine location of the tension axis.

Srinivasan, A. V.↗

NASA NTRS1945

Data for Design of Entrance Vanes from Two-Dimensional Tests of Airfoils in Cascade

As a part of a program of the NACA directed toward increasing the efficiency of compressors and turbines, data were obtained for application to the design of entrance vanes for axfax-flow compressors or turbines. A series of blower-blade sections with relatively high critical speeds have been developed for turning air efficiently from 0 deg to 80 deg starting with an axial direction. Tests were made of five NACA 65-series blower blades (modified NACA 65(216)-010 airfoils) and of four experimentally designed blower blades in a stationary cascade at low Mach numbers. The turning effectiveness and the pressure distributions of these blade sections at various angles of attack were evaluated over a range of solidities near 1. Entrance-vane design charts are presented that give a blade section and angle of attack for any desired turning angle. The blades thus obtained operate with peak-free pressure distributions. Approximate critical Mach numbers were calculated from the pressure distributions.

FLOW-VANES, GUIDE↗

NASA NTRS1993

An overview of shed ice impact in the NASA Lewis Icing Research Tunnel

One of the areas of active research in commercial and military rotorcraft is directed toward developing the capability of sustained flight in icing conditions. The emphasis to date has been on the accretion and subsequent shedding of ice in an icing environment, where the shedding may be natural or induced. Historically, shed-ice particles have been a problem for aircraft, particularly rotorcraft. Because of the high particle velocities involved, damage to a fuselage or other airframe component from a shed-ice impact can be significant. Design rules for damage tolerance from shed-ice impact are not well developed because of a lack of experimental data. Thus, NASA Lewis (LeRC) has begun an effort to develop a database of impact force and energy resulting from shed ice. This effort consisted of a test of NASA LeRC's Model Rotor Test Rig (MRTR) in the Icing Research Tunnel (IRT). Both natural shedding and forced shedding were investigated. Forced shedding was achieved by fitting the rotor blades with Small Tube Pneumatic (STP) deicer boots manufactured by BF Goodrich. A detailed description of the test is given as well as the design of a new impact sensor which measures the force-time history of an impacting ice fragment. A brief discussion of the procedure to infer impact energy from a force-time trace are required for the impact-energy calculations. Recommendations and future plans for this research area are also provided.

Bond, Thomas H.↗

NASA NTRS1993

An overview of shed ice impact studies in the NASA Lewis Icing Research Tunnel

Britton, Randall K.↗

NASA NTRS1981

Energy efficient engine shroudless, hollow fan blade technology report

The Shroudless, Hollow Fan Blade Technology program was structured to support the design, fabrication, and subsequent evaluation of advanced hollow and shroudless blades for the Energy Efficient Engine fan component. Rockwell International was initially selected to produce hollow airfoil specimens employing the superplastic forming/diffusion bonding (SPF/DB) fabrication technique. Rockwell demonstrated that a titanium hollow structure could be fabricated utilizing SPF/DB manufacturing methods. However, some problems such as sharp internal cavity radii and unsatisfactory secondary bonding of the edge and root details prevented production of the required quantity of fatigue test specimens. Subsequently, TRW was selected to (1) produce hollow airfoil test specimens utilizing a laminate-core/hot isostatic press/diffusion bond approach, and (2) manufacture full-size hollow prototype fan blades utilizing the technology that evolved from the specimen fabrication effort. TRW established elements of blade design and defined laminate-core/hot isostatic press/diffusion bonding fabrication techniques to produce test specimens. This fabrication technology was utilized to produce full size hollow fan blades in which the HIP'ed parts were cambered/twisted/isothermally forged, finish machined, and delivered to Pratt & Whitney Aircraft and NASA for further evaluation.

Michael, C. J.↗

NASA NTRS1975

Mechanical behavior of the directionally solidified gamma/gamma prime - delta eutectic alloy

The eutectic alloy Ni-20.0%Cb-2.5%Al-6.0%Cr was tested in short-term creep and long-term exposure to service conditions to assess its suitability for high temperature turbine blade applications. Long-time exposure showed the lamellar microstructure of the alloy to be exceptionally stable. Other properties tested were notch sensitivity, isothermal and thermomechanical fatigue strength, shear strength, and transverse ductility. It was shown that this alloy is superior to the best currently available directionally solidified superalloys over the temperature/stress conditions encountered in turbine airfoils.

Barkalow, R. H.↗

NASA NTRS1975

Thickness noise of helicopter rotors at high tip speeds

A new formulation of helicopter rotor thickness, noise for hover and forward flight, is discussed. The parameters required for this formulation are rotor motion, planform and airfoil thickness distribution. A computer program has been developed to calculate the pressure signature due to blade thickness for a helicopter in arbitrary motion. Comparison with high-speed helicopter tests shows good agreement with calculations when the observer is in or near the horizontal plane in which the rotor disk lies. Characteristics of thickness noise are illustrated by numerical examples indicating strongly that the high-speed blade slap may be due primarily to the thickness effect. The methods of Deming and Arnoldi are discussed as the special cases of this technique.

Farassat, F.↗

NASA NTRS1975

Thickness Noise of Helicopter Rotors at High Tip Speeds

A new formulation of helicopter rotor thickness, noise for hover and forward flight, is discussed. The parameters required for this formulation are rotor motion, planform and airfoil thickness distribution. A computer program has been developed to calculate the pressure signature due to blade thickness for a helicopter in arbitrary motion. Comparison with high-speed helicopter tests shows good agreement with calculations when the observer is in or near the horizontal plane in which the rotor disc lies. Characteristics of thickness noise are illustrated by numerical examples indicating strongly that the high-speed blade slap may be due primarily to the thickness effect. The methods of Deming and Arnoldi are discussed as the special cases of this technique.

Farassat, F.↗

NASA NTRS1989

Fluctuating pressures on wing surfaces in the slipstream of a single-rotor propfan

Measurements of the fluctuating pressure levels (FPLs) induced on a Propfan Test Assessment wing by the SR-7L propfan slipstream within the airplane flight envelope were obtained as a function of propfan operating conditions. It is shown that FPLS were high over most of the flight envelope, and that the spectra were dominated by the propfan first-order blade passage frequency tone. The highest FPLs were found at the lowest aircraft test altitudes and Mach numbers and for propfan conditions of lowest rotational tip speed and highest power.

Swift, G.↗

NASA NTRS2002

Unsteady Pressures in a Transonic Fan Cascade Due to a Single Oscillating Airfoil

An extensive set of unsteady pressure data was acquired along the midspan of a modern transonic fan blade for simulated flutter conditions. The data set was acquired in a nine-blade linear cascade with an oscillating middle blade to provide a database for the influence coefficient method to calculate instantaneous blade loadings. The cascade was set for an incidence of 10 dg. The data were acquired on three stationary blades on each side of the middle blade that was oscillated at an amplitude of 0.6 dg. The matrix of test conditions covered inlet Mach numbers of 0.5, 0.8, and 1.1 and the oscillation frequencies of 200, 300, 400, and 500 Hz. A simple quasiunsteady two-dimensional computer simulation was developed to aid in the running of the experimental program. For high Mach number subsonic inlet flows the blade pressures exhibit very strong, low-frequency, self-induced oscillations even without forced blade oscillations, while for low subsonic and supersonic inlet Mach numbers the blade pressure unsteadiness is quite low. The amplitude of forced pressure fluctuations on neighboring stationary blades strongly depends on the inlet Mach number and forcing frequency. The flowfield behavior is believed to be governed by strong nonlinear effects due to a combination of viscosity, compressibility, and unsteadiness. Therefore, the validity of the quasi-unsteady simplified computer simulation is limited to conditions when the flowfield is behaving in a linear, steady manner. Finally, an extensive set of unsteady pressure data was acquired to help development and verification of computer codes for blade flutter effects.

Lepicovsky, J.↗

NASA NTRS1982

A preliminary comparison between the SR-3 propeller noise in flight and in a wind tunnel

The noise generated by supersonic-tip-speed propellers is addressed. Models of such propellers were tested for acoustics in the Lewis 8-by-6-foot wind tunnel. One of these propeller models, SR-3, was tested in flight on the Jetstar airplane and noise data were obtained. Preliminary comparisons of the maximum blade passing tone variation with helical tip Mach number taken in flight with those taken in the tunnel showed good agreement when corrected to the same test conditions. This indicated that the wind tunnel is a viable location for measuring the noise of these propeller models. Comparisons of the directivities at 0.6 and 0.7 axial Mach number showed reasonable agreement. At 0.75 and 0.8 axial Mach number the tunnel directivity data fell off more towards the front than did the airplane data. A possible explanation for this is boundary layer refraction which could be different in the wind tunnel from that in flight. This may imply that some corrections should be applied to both the airplane and wind tunnel data at the forward angles. At and aft of the peak noise angle the boundary layer refraction does not appear to be significant and no correction appears necessary.

Dittmar, J. H.↗

NASA NTRS1952

An Investigation of the Effect of the WADC 30,000-Horsepower Whirl Rig Upon the Static Characteristics of a Propeller

Tests have been made at the Langley Aeronautical Laboratory on a 6000-horsepower propeller dynamometer installed at a ground test facility to determine the effect of a half-scale model of the Wright Aeronautical Development Center 30,000-horsepower whirl rig upon the aerodynamic characteristics of a three-blade NACA 10-(3)(062)-045 propeller. The model of the whirl rig was mounted in front of the 6000-horsepower propeller dynamometer. Static propeller tests were made for 0deg, 5deg, 10deg, 15deg, and 20deg blade angles over a range of rotational speeds from 600 to 2200 rpm in 100-rpm increments. Measurements were made of propeller thrust and torque, stresses in the propeller blades, and static and total pressures over the surface of the model. Propeller thrust and torque were increased up to 33 percent by the presence of the model of the whirl rig, but the average increase was from 5 to 10 percent. Blade vibratory stresses were small.

Salters, Leland B., Jr.↗

NASA NTRS1979

Parameter identification applied to analytic hingeless rotor modeling

It is known that dynamic rotor inflow has a substantial effect on rotor dynamic loads. Despite the complexity of the unsteady flow problem, simple analytical models can be made useful by identifying their parameters from transient response tests without performing flow measurements. Two analytical inflow models are studied: the first is based on an equivalent blade Lock number, the second is based on a time delayed unsteady momentum inflow. In preparation for the experimental data analysis, identifications from simulated test data and an eigenvalue analysis are performed. The experimental results show that the first analytical inflow model is accurate for rotor advance ratios of 0.4 and above. For lower advance ratios, the second inflow model provides better accuracy. Prediction studies with experimental data not used for the identification are performed to determine the accuracy of the mathematical models.

Banerjee, D.↗