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At least 325 records · Page 18

All sources NASA NTRS DOE OSTI

NASA NTRS1986

A study of helicopter main rotor noise in hover

Some fundamental aspects of rotor noise generation and radiation are presented. Data on which the study is based were obtained during a hover test at the NASA Ames Outdoor Aerodynamic Research Facility of a one-sixth-scale, four-bladed, helicopter rotor. The test site provided an open environment ideal for acquiring good acoustic data. Information is presented on the delineation between the acoustic near-field and far-field, and on the effect of a simple boundary-layer trip device. Data obtained at near-zero thrust conditions indicate that it is possible to isolate thickness noise with minimum contamination by loading noise effects. An abrupt change in the nature of the emitted noise at high-thrust conditions is investigated and is related to unsteady wake/support interaction.

Kitaplioglu, C.↗

NASA NTRSDate not supplied

Extreme Environment Hot Fire Durability of Post-Processed Additively Manufactured GRCop-Alloy Combustion Chambers in LOX/Hydrogen and LOX/Methane

Extreme environment survivability of metal additive manufactured (AM) GRCop-alloy thrust chambers has been demonstrated in different bi-propellants at near stoichiometric and even oxygen rich combustion. GRCop-alloy chambers tested at NASA Marshall Space Flight Center (MSFC) have accumulated over 26,000 seconds of hot fire duration and over 500 starts. These chambers are produced using an AM process called laser powder bed fusion (L-PBF). A major feature of this process is high wall surface roughness which can be customized in post processing to leverage various performance advantages. Post-processing can include heat treatment, final machining, polishing, and welding and is key to hardware survivability in extreme environments. Surface finish enhancement techniques were applied to the hot wall and coolant channels to reduce the overall total heat load to the chamber walls. Performance optimization of various thrust class TCA’s is a strategic technology goal of NASA MSFC. Three different chamber geometries using cryogenic methane and de-ionized water as coolants were hot fire tested to obtain their life cycle, pressure drop, and heat load performances. Several 1.2K lbf LOX/H2 chambers, 1K lbf LOX/CH4 chambers, and 7K lbf LOX/CH4 chambers were tested. All post-processed configurations performed remarkably well when subjected to extreme hot fire test conditions. Streaking and blanching due to localized oxygen rich conditions were observed on some test articles in their as-built surface finish state. However, this is actually a function of the injector mixing and only serves to further establish the durability of L-PBF GRCop-alloy thrust chambers. Several different polishing techniques were applied to the hot wall and integrated coolant channels prior to hot fire testing and their performances assessed. Overall, AM produced GRCop chambers are extremely reliable, durable, and customizable to the desired performance metrics.

grcop↗

NASA NTRS1997

Vortex Core Size in the Rotor Near-Wake

Using a kinetic energy conservation approach, a number of simple analytic expressions are derived for estimating core size of tip vortices in the near-wake of rotors in hover or axial-flight (climb). The influence of thrust, axial-flight advance ratio, blade count, blade aspect ratio, nonuniform disk loading, and vortex structure on rotor vortex core size is assessed. Vortex core size is found to be directly proportional to rotor thrust and inversely proportional to axial-flight advance ratio. Further, it is found that the more efficient the rotor is with respect to factors that affect induced power, the smaller the vortex core size. In particular, uniformity of the rotor disk loading clearly has the greatest influence on vortex core size of the parameters studied in this paper.

Young, Larry A.↗

NASA NTRS2008

Transient Three-Dimensional Side Load Analysis of a Film Cooled Nozzle

Transient three-dimensional numerical investigations on the side load physics for an engine encompassing a film cooled nozzle extension and a regeneratively cooled thrust chamber, were performed. The objectives of this study are to identify the three-dimensional side load physics and to compute the associated aerodynamic side load using an anchored computational methodology. The computational methodology is based on an unstructured-grid, pressure-based computational fluid dynamics formulation, and a transient inlet history based on an engine system simulation. Ultimately, the computational results will be provided to the nozzle designers for estimating of effect of the peak side load on the nozzle structure. Computations simulating engine startup at ambient pressures corresponding to sea level and three high altitudes were performed. In addition, computations for both engine startup and shutdown transients were also performed for a stub nozzle, operating at sea level. For engine with the full nozzle extension, computational result shows starting up at sea level, the peak side load occurs when the lambda shock steps into the turbine exhaust flow, while the side load caused by the transition from free-shock separation to restricted-shock separation comes at second; and the side loads decreasing rapidly and progressively as the ambient pressure decreases. For the stub nozzle operating at sea level, the computed side loads during both startup and shutdown becomes very small due to the much reduced flow area.

Wang, Ten-See↗

NASA NTRS1971

Experimental techniques for evaluating steady-state jet engine performance in an altitude facility

Jet engine calibration tests were conducted in an altitude facility using a contoured bellmouth inlet duct, four fixed-area water-cooled exhaust nozzles, and an accurately calibrated thrust measuring system. Accurate determination of the airflow measuring station flow coefficient, the flow and thrust coefficients of the exhaust nozzles, and the experimental and theoretical terms in the nozzle gross thrust equation were some of the objectives of the tests. A primary objective was to develop a technique to determine gross thrust for the turbojet engine used in this test that could also be used for future engine and nozzle evaluation tests. The probable error in airflow measurement was found to be approximately 0.6 percent at the bellmouth throat design Mach number of 0.6. The probable error in nozzle gross thrust measurement was approximated 0.6 percent at the load cell full-scale reading.

Smith, J. M.↗

NASA NTRS1979

Weight and cost estimating relationships for heavy lift airships

Weight and cost estimating relationships, including additional parameters that influence the cost and performance of heavy-lift airships (HLA), are discussed. Inputs to a closed loop computer program, consisting of useful load, forward speed, lift module positive or negative thrust, and rotors and propellers, are examined. Detail is given to the HLA cost and weight program (HLACW), which computes component weights, vehicle size, buoyancy lift, rotor and propellar thrust, and engine horse power. This program solves the problem of interrelating the different aerostat, rotors, engines and propeller sizes. Six sets of 'default parameters' are left for the operator to change during each computer run enabling slight data manipulation without altering the program.

Gray, D. W.↗

NASA NTRS1982

Structures: Propulsion interactions and requirements

The dynamics of the interaction of space structures and their propellant systems are outlined. Optimization for a platform type of space structure is discussed. Static and transient loads, propellant accelerations, tolerances, attitude control, and distributed thrust are considered.

Pengelley, C. D.↗

NASA NTRS1983

Study of auxiliary propulsion requirements for large space systems, volume 2

A range of single shuttle launched large space systems were identified and characterized including a NASTRAN and loading dynamics analysis. The disturbance environment, characterization of thrust level and APS mass requirements, and a study of APS/LSS interactions were analyzed. State-of-the-art capabilities for chemical and ion propulsion were compared with the generated propulsion requirements to assess the state-of-the-art limitations and benefits of enhancing current technology.

Smith, W. W.↗

NASA NTRS1988

Pressure measurements of impinging jet with asymmetric nozzle

For modern aircraft, impinging surfaces are commonly used as a device for obtaining vector thrust from engine exhaust. The nature of dynamic loading is important to understand for design purposes. In this study, the frequency, mode, and level of pressure fluctuations generated by an elliptic jet are examined. The elliptic jet is used because it has several operational advantages over a circular jet.

Ho, Chih-Ming↗

NASA NTRS1987

Compromise - An effective approach for conceptual aircraft design

The Decision Support Problem (DSP) technique for aircraft design is presently demonstrated through the development of a compromise DSP template for the conceptual design of subsonic transport aircraft. System variables are wing span and area, fuselage diameter and length, takeoff weight, and installed thrust. Such system constraints as range and wing loading are represented algebraically using standard subsonic aircraft theory, and economic efficiency is modeled in terms of rates-of-return. The DSP template thus obtained has been tested and validated using the known mission requirements and design constants of the B 727-200 airliner.

Mistree, Farrokh↗

NASA NTRS1989

Nonlinear maneuver autopilot for the F-15 aircraft

A methodology is described for the development of flight test trajectory control laws based on singular perturbation methodology and nonlinear dynamic modeling. The control design methodology is applied to a detailed nonlinear six degree-of-freedom simulation of the F-15 and results for a level accelerations, pushover/pullup maneuver, zoom and pushover maneuver, excess thrust windup turn, constant thrust windup turn, and a constant dynamic pressure/constant load factor trajectory are presented.

Menon, P. K. A.↗

NASA NTRS1989

Boundary layer simulator improvement

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Praharaj, Sarat C.↗

NASA NTRS2003

1-Way Bearing

A one-way bearing is provided having sprags and rolling bearings both disposed between an inner and an outer race. The sprags may comprise three-dimensional sprags for preventing rotation in a non-preferential direction. The roll- ing bearings may comprise thrust rollers for transmitting axial, tilt, and radial loads between the inner and outer races.

Vranish, John M.↗

NASA NTRS2008

Rotor Airloads Prediction Using Unstructured Meshes and Loose CFD/CSD Coupling

The FUN3D unsteady Reynolds-averaged Navier-Stokes solver for unstructured grids has been modified to allow prediction of trimmed rotorcraft airloads. The trim of the rotorcraft and the aeroelastic deformation of the rotor blades are accounted for via loose coupling with the CAMRAD II rotorcraft computational structural dynamics code. The set of codes is used to analyze the HART-II Baseline, Minimum Noise and Minimum Vibration test conditions. The loose coupling approach is found to be stable and convergent for the cases considered. Comparison of the resulting airloads and structural deformations with experimentally measured data is presented. The effect of grid resolution and temporal accuracy is examined. Rotorcraft airloads prediction presents a very substantial challenge for Computational Fluid Dynamics (CFD). Not only must the unsteady nature of the flow be accurately modeled, but since most rotorcraft blades are not structurally stiff, an accurate simulation must account for the blade structural dynamics. In addition, trim of the rotorcraft to desired thrust and moment targets depends on both aerodynamic loads and structural deformation, and vice versa. Further, interaction of the fuselage with the rotor flow field can be important, so that relative motion between the blades and the fuselage must be accommodated. Thus a complete simulation requires coupled aerodynamics, structures and trim, with the ability to model geometrically complex configurations. NASA has recently initiated a Subsonic Rotary Wing (SRW) Project under the overall Fundamental Aeronautics Program. Within the context of SRW are efforts aimed at furthering the state of the art of high-fidelity rotorcraft flow simulations, using both structured and unstructured meshes. Structured-mesh solvers have an advantage in computation speed, but even though remarkably complex configurations may be accommodated using the overset grid approach, generation of complex structured-mesh systems can require months to set up. As a result, many rotorcraft simulations using structured-grid CFD neglect the fuselage. On the other hand, unstructured-mesh solvers are easily able to handle complex geometries, but suffer from slower execution speed. However, advances in both computer hardware and CFD algorithms have made previously state-of-the-art computations routine for unstructured-mesh solvers, so that rotorcraft simulations using unstructured grids are now viable. The aim of the present work is to develop a first principles rotorcraft simulation tool based on an unstructured CFD solver.

Biedron, Robert T.↗

DOE OSTI2024

In-Situ Blade Strain Measurements and Fatigue Analysis of a Cross-Flow Turbine Operating in a Tidal Flow

Cross-flow turbines (CFTs) are inherently unsteady devices with regards to operating principle and loading. By improving our understanding of the dynamic loading on these turbines, we hope to better inform CFT design, improve survivability, and reduce overall costs. The University of New Hampshire (UNH) and the National Renewable Energy Laboratory (NREL) collaborated on a project to instrument and test a four-bladed New Energy Corp. vertical axis cross-flow turbine in a real tidal flow. One blade from the 3.2 m diameter x 1.7 m height turbine was instrumented with eight full-bridge strain gauges along the span of the blade. The turbine was then deployed at the UNH-Atlantic Marine Energy Center (AMEC) Tidal Energy Test Site in Portsmouth, NH. Time-synchronized measurements of blade strain, inflow, thrust, rotational speed, and electrical output were obtained to characterize blade loading under various conditions. The blade strain was examined to assess the dynamic loading and conduct a fatigue analysis on the device.

blade strain↗

NASA NTRS1998

Preliminary In-Flight Loads Analysis of In-Line Launch Vehicles using the VLOADS 1.4 Program

To calculate structural loads of in-line launch vehicles for preliminary design, a very useful computer program is VLOADS 1.4. This software may also be used to calculate structural loads for upper stages and planetary transfer vehicles. Launch vehicle inputs such as aerodynamic coefficients, mass properties, propellants, engine thrusts, and performance data are compiled and analyzed by VLOADS to produce distributed shear loads, bending moments, axial forces, and vehicle line loads as a function of X-station along the vehicle's length. Interface loads, if any, and translational accelerations are also computed. The major strength of the software is that it enables quick turnaround analysis of structural loads for launch vehicles during the preliminary design stage of its development. This represents a significant improvement over the alternative-the time-consuming, and expensive chore of developing finite element models. VLOADS was developed as a Visual BASIC macro in a Microsoft Excel 5.0 work book on a Macintosh. VLOADS has also been implemented on a PC computer using Microsoft Excel 7.0a for Windows 95. VLOADS was developed in 1996, and the current version was released to COSMIC, NASA's Software Technology Transfer Center, in 1997. The program is a copyrighted work with all copyright vested in NASA.

Graham, J. B.↗

NASA NTRS1977

Vortex attenuation flight experiments

Flight tests evaluating the effects of altered span loading, turbulence ingestion, combinations of mass and turbulence ingestion, and combinations of altered span loading turbulance ingestion on trailed wake vortex attenuation were conducted. Span loadings were altered in flight by varying the deflections of the inboard and outboard flaps on a B-747 aircraft. Turbulence ingestion was achieved in flight by mounting splines on a C-54G aircraft. Mass and turbulence ingestion was achieved in flight by varying the thrust on the B-747 aircraft. Combinations of altered span loading and turbulence ingestion were achieved in flight by installing a spoiler on a CV-990 aircraft and by deflecting the existing spoilers on a B-747 aircraft. The characteristics of the attenuated and unattenuated vortexes were determined by probing them with smaller aircraft. Acceptable separation distances for encounters with the attenuated and unattenuated vortexes are presented.

Barber, M. R.↗

NASA NTRS1987

Finite element analysis of steady and transiently moving/rolling nonlinear viscoelastic structure. II - Shell and three-dimensional simulations

In a three-part series of papers, a generalized finite element solution strategy is developed to handle traveling load problems in rolling, moving and rotating structure. The main thrust of this section consists of the development of three-dimensional and shell type moving elements. In conjunction with this work, a compatible three-dimensional contact strategy is also developed. Based on these modeling capabilities, extensive analytical and experimental benchmarking is presented. Such testing includes traveling loads in rotating structure as well as low- and high-speed rolling contact involving standing wave-type response behavior. These point to the excellent modeling capabilities of moving element strategies.

Kennedy, Ronald↗