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NASA NTRS2005

Optical Sensing of Combustion Instabilities in Gas Turbines

In a continuing program of research and development, a system has been demonstrated that makes high-speed measurements of thermal infrared radiance from gas-turbine engine exhaust streams. When a gas-turbine engine is operated under conditions that minimize the emission of pollutants, there is a risk of crossing the boundary from stable to unstable combustion. Combustion instability can lead to engine damage and even catastrophic failure. Sensor systems of the type under development could provide valuable data during the development testing of gas-turbine engines or of engine components. A system of the type under development makes high-speed measurements of thermal infrared radiance from the engine exhaust stream. The sensors of this system can be mounted outside the engine, which eliminates the need for engine case penetrations typical with other engine dynamics monitors. This is an important advantage in that turbine-engine manufacturers consider such penetrations to be very undesirable. A prototype infrared sensor system has been built and demonstrated on a turbine engine. This system includes rugged and inexpensive near-infrared sensors and filters that select wavelengths of infrared radiation for high sensitivity. In experiments, low-frequency signatures were consistently observed in the detector outputs. Under some conditions, the signatures also included frequency components having one or two radiance cycles per engine revolution. Although it has yet to be verified, it is thought that the low-frequency signatures may be associated with bulk-mode combustion instabilities or flow instabilities in the compressor section of the engine, while the engine- revolution-related signatures may be indicative of mechanical problems in the engine. The system also demonstrated the ability to detect transient high-radiance events. These events indicate hot spots in the exhaust stream and were found to increase in frequency during engine acceleration.

Markham, James R.↗

NASA NTRS2012

Model-Based Verification and Validation of Spacecraft Avionics

Verification and Validation (V&V) at JPL is traditionally performed on flight or flight-like hardware running flight software. For some time, the complexity of avionics has increased exponentially while the time allocated for system integration and associated V&V testing has remained fixed. There is an increasing need to perform comprehensive system level V&V using modeling and simulation, and to use scarce hardware testing time to validate models; the norm for thermal and structural V&V for some time. Our approach extends model-based V&V to electronics and software through functional and structural models implemented in SysML. We develop component models of electronics and software that are validated by comparison with test results from actual equipment. The models are then simulated enabling a more complete set of test cases than possible on flight hardware. SysML simulations provide access and control of internal nodes that may not be available in physical systems. This is particularly helpful in testing fault protection behaviors when injecting faults is either not possible or potentially damaging to the hardware. We can also model both hardware and software behaviors in SysML, which allows us to simulate hardware and software interactions. With an integrated model and simulation capability we can evaluate the hardware and software interactions and identify problems sooner. The primary missing piece is validating SysML model correctness against hardware; this experiment demonstrated such an approach is possible.

MBV&V↗

NASA NTRSDate not supplied

Assessing the Effects of Various Surface Textures and Features on Turbulent Heat Transfer in Hypersonic Flight

Experiments were conducted in the NASA Ames Hypervelocity Free Flight Aerodynamic Facility (ballistic range) to quantify the effects on turbulent convective heat transfer of distributed surface roughness, and of isolated features, representative of thermal protection systems on atmospheric entry vehicles. The surface textures and features were applied on the conic frusta of 45o sphere-cone models having a nose-to-base radius ratio of 0.5, similar to the forebody geometry of the Galileo and Pioneer-Venus entry probes. Test conditions were selected to provide turbulent roughness Reynolds numbers, k+, in the ranges expected for outer planet entry missions. Turbulent flow on the conic frustum was achieved by tripping the flow on the sphere-segment nose cap with distributed surface roughness, created by sand-blasting the nose cap. Surface textures included distributed, acreage, roughness, as well as cavity and groove discrete features. The majority of the data to be presented are results for distributed roughness, which includes both random, sand-grain-like roughness, and regular pattern roughness. The pattern roughness was designed to represent the roughness on woven thermal protection system materials, such as NASA’s 3-D Medium Density Carbon Phenolic (3MDCP), also known as HEEET, developed by the Heatshield for Extreme Entry Environments Technology project. The pattern roughness tested is a 3-D wavy surface, and includes three different roughness element height-to-spacing ratios representative of two configurations of 3MDCP, and spanning ratios measured both before, and after, ablation in an arc jet test facility. The patterns tested in the ballistic range were laser-etched on metal models, and represented an idealized version of the real-world materials in which each roughness element was nearly identical. Additional tests were performed wherein the laser-etched patterns were degraded by sand-blasting with various sized grit media, to produce regular patterns with superimposed irregular roughness, more representative of flight materials. Results of each will be compared. The discrete features tested included cylindrical cavities and rectangular grooves of various width-to-depth ratios. Cavities represent either heatshield damage, such as from micro-meteoroid and orbital debris (MMOD) damage, or from designed penetrations, such as on the Genesis sample return capsule. The grooves were scaled representations of seams between segments of HEEET material in a notional tiled thermal protection system. The tests examined the effects on turbulent heating downstream of the isolated features. The tests were conducted at speeds between 3 km/s and 4 km/s in air between 0.15 atm and 0.25 atm (Mach numbers between 9 and 12). Roughness Reynolds numbers, k+, ranged from 12 to 70 for the sand roughness, and as high as 200 for the pattern roughness. Boundary-layer parameters required for calculating k+ were evaluated using computational fluid dynamics simulations using the DPLR (Data Parallel Line Relaxation) code. Each model included both rough- and smooth-wall segments, and heat transfer augmentation factors were determined as the ratio of the rough-wall to smooth-wall heat flux measured on each test.

hypersonic↗

NASA NTRS2005

Flight Test Implementation of a Second Generation Intelligent Flight Control System

The NASA F-15 Intelligent Flight Control System project team has developed a series of flight control concepts designed to demonstrate the benefits of a neural network-based adaptive controller. The objective of the team was to develop and flight-test control systems that use neural network technology, to optimize the performance of the aircraft under nominal conditions, and to stabilize the aircraft under failure conditions. Failure conditions include locked or failed control surfaces as well as unforeseen damage that might occur to the aircraft in flight. The Intelligent Flight Control System team is currently in the process of implementing a second generation control scheme, collectively known as Generation 2 or Gen 2, for flight testing on the NASA F-15 aircraft. This report describes the Gen 2 system as implemented by the team for flight test evaluation. Simulation results are shown which describe the experiment to be performed in flight and highlight the ways in which the Gen 2 system meets the defined objectives.

Williams-Hayes, Peggy S.↗

NASA NTRS1992

Static and dynamic strain energy release rates in toughened thermosetting composite laminates

In this work, the static and dynamic fracture properties of several thermosetting resin based composite laminates are presented. Two classes of materials are explored. These are homogeneous, thermosetting resins and toughened, multi-phase, thermosetting resin systems. Multi-phase resin materials have shown enhancement over homogenous materials with respect to damage resistance. The development of new dynamic tests are presented for composite laminates based on Width Tapered Double Cantilevered Beam (WTDCB) for Mode 1 fracture and the End Notched Flexure (ENF) specimen. The WTDCB sample was loaded via a low inertia, pneumatic cylinder to produce rapid cross-head displacements. A high rate, piezo-electric load cell and an accelerometer were mounted on the specimen. A digital oscilloscope was used for data acquisition. Typical static and dynamic load versus displacement plots are presented. The ENF specimen was impacted in three point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions were determined analytically and experimentally. The test results for Mode 1 fracture are relatively insensitive to strain rate effects for the laminates tested in this study. The test results from Mode 2 fracture indicate that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. While the static fracture properties of the homogeneous systems may be relatively high, the apparent Mode 2 dynamic critical strain energy release rate drops significantly. The results indicate that static Mode 2 fracture testing is inadequate for determining the fracture performance of composite structures subjected to conditions such as low velocity impact. A good correlation between the basic Mode 2 dynamic fracture properties and the performance is a combined material/structural Compression After Impact (CAI) test is found. These results underscore the importance of examining rate-dependent behavior for determining the longevity of structures manufactured from composite materials.

Cairns, Douglas S.↗

NASA NTRS2005

Rotordynamic Analysis and Feasibility Study of a Disk Spin Test Facility for Rotor Health Monitoring

Recently, National Aeronautics and Space Administration (NASA) initiated a program to achieve the significant improvement in aviation safety. One of the technical challenges is the design and development of accelerated experiments that mimic critical damage cases encountered in engine components. The Nondestructive Evaluation (NDE) Group at the NASA Glenn Research Center (GRC) is currently addressing the goal concerning propulsion health management and the development of propulsion system specific technologies intended to detect potential failures prior to catastrophe. For this goal the unique disk spin simulation system was assembled at NASA GRC, which allows testing of rotors with the spinning speeds up to 10K RPM, and at the elevated temperature environment reaching 540 C (1000 F). It is anticipated that the facility can be employed for detection of Low Cycle Fatigue disk cracking and further High Cycle Fatigue blade vibration. The controlled crack growth studies at room and elevated temperatures can be conducted on the turbine wheels, and various NDE techniques can be integrated and assessed as in-situ damage monitoring tools. Critical rotating parts in advanced gas turbine engines such as turbine disks frequently operate at high temperature and stress for long periods of time. The integrity of these parts must be proven by non-destructive evaluation (NDE) during various machining steps ranging from forging blank to finished shape, and also during the systematic overhaul inspections. Conventional NDE methods, however, have unacceptable limits. Some of these techniques are time-consuming and inconvenient for service aircraft testing. Almost all of these techniques require that the vicinity of the damage is known in advance. These experimental techniques can provide only local information and no indication of the structural strength at a component and/or system level. The shortcomings of currently available NDE methods lead to the requirement of new damage detection techniques that can provide global information on the rotating components/system, and, in addition, they do not require direct human access to the operating system. During this period of research considerable effort was directed towards the further development of experimental facility and development of the vibration-based crack detection methodology for rotating disks and shafts. A collection of papers and reports were written to describe the results of this work. The attached captures that effort and represents the research output during the grant period.

Sawicki, Jerzy T.↗

NASA NTRS1971

Shock and vibration tests of a SNAP-8 NaK pump

The pump used for reactor cooling in the SNAP 8 space power system was subjected to the expected vehicle launch vibration, and shock loading in accordance with the SNAP 8 environmental specification. Subsequent disassembly revealed damage to the thrust bearing pins, which should be redesigned and strengthened. The unit was operational, however, when run in a test loop after reassembly.

Stromquist, A. J.↗

NASA NTRS2009

Effect of Electrostatic Discharge on Electrical Characteristics of Discrete Electronic Components

This article reports on preliminary results of a study conducted to examine how temporary electrical overstress seed fault conditions in discrete power electronic components that cannot be detected with reliability tests but impact longevity of the device. These defects do not result in formal parametric failures per datasheet specifications, but result in substantial change in the electrical characteristics when compared with pristine device parameters. Tests were carried out on commercially available 600V IGBT devices using transmission line pulse (TLP) and system level ESD stress. It was hypothesized that the ESD causes local damage during the ESD discharge which may greatly accelerate degradation mechanisms and thus reduce the life of the components. This hypothesis was explored in simulation studies where different types of damage were imposed to different parts of the device. Experimental results agree qualitatively with the simulation for a number of tests which will motivate more in-depth modeling of the damage.

Wysocki, Phil↗

DOE OSTI2021

Skin factor and potential formation damage from chemical and mechanical processes in a naturally fractured carbonate aquifer with implications to CO 2 sequestration

Here, in this study, we investigate formation damage due to acidization and water injection tests into the naturally fractured carbonate Middle Duperow Formation at Kevin Dome, Montana, potentially diminishing the chance of a future successful Geological Carbon Sequestration (GCS) project. Multiple well-test analytical models, correlated with core description and lithology data, are used to determine flow behavior and communication between the water injection interval and surrounding formations. An improved three-dimensional (3D) geologic model with dual-continuum matrix and fracture properties is constructed based on most recent seismic, core, and water sample measurements. Brine injection is simulated to verify the interpretation from the analytical models, followed by CO 2 injection simulation. Geochemical calculations are performed to understand the in-situ processes that led to formation damage. Our findings suggest: (1) there are two possible scenarios that could lead to a positive total effective skin factor and permeability decline: partial penetration and formation damage; (2) analytical models indicate a positive total skin factor, contradicting results of a previous study suggesting that the well was mildly stimulated; (3) numerical simulation supports the formation damage hypothesis by matching the pressure buildup observed during the latter two brine injection tests; (4) several mechanical and chemical processes may have occurred during injection to clog the matrix/fracture system: anhydrite fines migration and/or calcite precipitation. We then make preventative suggestions for future GCS projects into carbonate reservoirs and remediation recommendations for GCS operation at the Kevin Dome.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2011

Solar Dynamics Observatory On-Orbit Jitter Testing, Analysis, and Mitigation Plans

The Solar Dynamics Observatory (SDO) was designed to understand the Sun and the Sun s influence on Earth. SDO was launched on February 11, 2010 carrying three scientific instruments: the Atmospheric Imaging Assembly (AIA), the Helioseismic and Magnetic Imager (HMI), and the Extreme Ultraviolet Variability Experiment (EVE). Both AIA and HMI are sensitive to high frequency pointing perturbations and have sub-arcsecond level line-of-sight (LOS) jitter requirements. Extensive modeling and analysis efforts were directed in estimating the amount of jitter disturbing the science instruments. To verify the disturbance models and to validate the jitter performance prior to launch, many jitter-critical components and subassemblies were tested either by the mechanism vendors or at the NASA Goddard Space Flight Center (GSFC). Although detailed analysis and assembly level tests were performed to obtain good jitter predictions, there were still several sources of uncertainties in the system. The structural finite element model did not have all the modes correlated to test data at high frequencies (greater than 50 Hz). The performance of the instrument stabilization system was not known exactly but was expected to be close to the analytical model. A true disturbance-to-LOS observatory level test was not available due to the tight schedule of the flight spacecraft, the cost in time and manpower, difficulties in creating gravity negation systems, and risks of damaging flight hardware. To protect the observatory jitter performance against model uncertainties, the SDO jitter team devised several on-orbit jitter reduction plans in addition to reserve margins on analysis results. Since some of these plans severely restricted the capabilities of several spacecraft components (e.g. wheels and High Gain Antennas), the SDO team performed on-orbit jitter tests to determine which jitter reduction plans, if any, were necessary to satisfy science LOS jitter requirements. The SDO on-orbit jitter tests were designed to satisfy the following four objectives: 1. Determine the acceptable reaction wheel operational speed range during Science Mode. 2. Determine HGA algorithm jitter parameters (number of stagger steps and enable/disable no-steprequests). 3. Determine acceptable EVE instrument filter wheels spin rates. 4. Determine if AIA instrument filter wheels excite the first AIA telescope structural mode. This paper provides detailed information on the SDO wheel jitter test plan, shows on-orbit jitter measurements and how ground predictions compare to those measurements, and describes the final jitter mitigation plan executed on SDO.

Liu, Kuo-Chia (Alice)↗

NASA NTRSDate not supplied

Simulation of Dust-Laden Flow in the DLR L2K Facility

An integrated CFD-particle trajectory code called US3D-DUST is used to simulate the dusty flow environments performed in the German Aerospace Center (DLR) L2K arcjet facility. The particle trajectory code uses a Lagrangian approach, where the particle trajectories through the shock layer can be computed using a set of coupled ordinary differential equations. The L2K experiments measured mass loss to flat-face shaped samples of the Norcoat-Liège thermal protection system material. The US3D-DUST simulations were able to reproduce particle velocity and stagnation point heating rate data. When applied to the L2K dusty flow conditions, the US3D-DUST predictions of mass loss due to particle impacts and surface recession rates over-predicted the experimental values. It is recommended to perform additional dusty flow tests in the L2Kto provide and improve the surface damage model for Norcoat-Liège.

Thermal protection systems↗

NASA NTRS1981

Beam stresses induced by a turbulent boundary layer and simulated with a reverberant acoustic field

Unsteady pressure fluctuations are a feature of the flow field of an airplane or a space vehicle in atmospheric flight. Undesirable effects of these fluctuations range from internal (cabin) noise to structural fatigue and damage of avionic and ordnance systems. The integrity to withstand these fluctuating loads is established through reverberant room acoustical qualification testing. The purpose of this paper is to develop a methodology of simulating turbulent boundary layer fluctuating pressure loading for a simply supported beam with a reverberant acoustic field. This goal was accomplished using normal mode vibration analysis. The main results were developed in terms of dimensionless quantities such as turbulent boundary layer spectrums, reverberant acoustical field simulation spectrums, and stress response spectrums with parameters: dimensionless fundamental frequency, Mach number, and relative boundary layer displacement thickness.

Schutzenhofer, L. A.↗

NASA NTRS1984

Infrared technology for satellite power conversion

Successful fabrication of bismuth bolometers led to the observation of antenna action rom array elements. Fabrication of the best antennas arrays was made more facile with finding that increased argon flow during the dc sputtering produced more uniform bismuth films and bonding to antennas must be done with the substrate temperaure below 100 C. Higher temperatures damaged the bolometers. During the testing of the antennas, it was found that the use of a quasi-optical system provided a uniform radiation field. Groups of antennas were bonded in series and in parallel with the parallel configuration showing the greater response.

Campbell, D. P.↗

NASA NTRS1989

Expansion and orthogonalization of measured modes for structure identification

The purpose was to investigate a new simultaneous expansion/orthogonalization method in comparison with two previously published expansion methods and a widely used orthogonalization technique. Each expansion method uses data from an analytical model of the structure to complete the estimate of the mode shape vectors. Berman and Nagy used Guyan expansion in their work with improving analytical models. In this method, modes are expanded one at a time, producing a set not orthogonal with respect to the mass matrix. Baruch and Bar Itzhack's optimal orthogonalization procedure was used to subsequently adjust the expanded modes. A second expansion technique was presented by O'Callahan, Avitabile, and Reimer and separately by Kammer. Again, modes are expanded individually and orthogonalized after expansion with the same optimal technique as above. Finally, a simultaneous expansion/orthogonalization method was developed from the orthogonal Procrustes problem of computational mathematics. In this method modes are optimally expanded as a set and orthogonal with respect to the mass matrix as a result. Two demonstation problems were selected for the comparison of the methods described. The first problem is an 8 degree of freedom spring-mass problem first presented by Kabe. Several conditions were examined for expansion method including the presence of errors in the measured data and in the analysis models. As a second demonstration problem, data from tests of laboratory scale model truss structures was expanded for system identification. Tests with a complete structure produced a correlated analysis model and the stiffness and mass matrices. Tests of various damaged configurations produced measured data for 6 modes at 14 dof locations.

Smith, Suzanne Weaver↗

DOE OSTI2024

Non-contact Real-time Target Health Monitor

Targets are an essential part of many accelerator-based experiments, yet their constant radiation exposure eventually affects their internal structure and, consequently, their properties. Current methods typically involve either direct contact with the target or complete removal of the system, which may not be the most efficient for assessing radiation damage. For this reason, a system has been proposed that will monitor a target s radiation damage without the need for direct contact or removal. This sensor will achieve this by measuring the reflectivity of S- and P-polarized waves, which are expected to change measurably due to radiation-induced alterations. As is commonly done, smaller-scale tests were performed to ensure that the necessary equipment was functioning correctly. Once all equipment is tested, the next step will be to perform reflectivity measurements using a tungsten sample, a material often used in targets. Longer-term work will involve scaling up the system and implementing higher-energy beams. This sensor will enable a more comprehensive study of radiation damage in materials and is being considered for projects such as Mu2e, Mu2e-II, LBNF, AMF, and muon colliders.

Agosto Reyes, Alanice↗

DOE OSTI2024

Non-contact Real-time Target Health Monitor

Agosto Reyes, Alanice↗

NASA NTRS2008

On-orbit Passive Thermography

On July 12, 2006, British-born astronaut Piers Sellers became the first person to conduct thermal nondestructive evaluation experiments in space, demonstrating the feasibility of a new tool for detecting damage to the reinforced carbon-carbon (RCC) structures of the Shuttle. This new tool was an EVA (Extravehicular Activity, or spacewalk) compatible infrared camera developed by NASA engineers. Data was collected both on the wing leading edge of the Orbiter and on pre-damaged samples mounted in the Shuttle s cargo bay. A total of 10 infrared movies were collected during the EVA totaling over 250 megabytes of data. Images were downloaded from the orbiting Shuttle to Johnson Space Center for analysis and processing. Results are shown to be comparable to ground-based thermal inspections performed in the laboratory with the same type of camera and simulated solar heating. The EVA camera system detected flat-bottom holes as small as 2.54cm in diameter with 50% material loss from the back (hidden) surface in RCC during this first test of the EVA IR Camera. Data for the time history of the specimen temperature and the capability of the inspection system for imaging impact damage are presented.

Howell, Patricia A.↗

DOE OSTI2024

Evaluation of Clamshell Current Coupler for Online Frequency Domain and Spread Spectrum Time Domain Reflectometry to Detect Anomalies in Energized Cables

This document describes adaptation and evaluation of a clamshell inductive current coupler for online reflectometry testing (both frequency domain reflectometry and spread spectrum time domain reflectometry) to evaluate cable insulation degradation and anomalies. Safety-critical nuclear power plant cables were initially qualified for 40 years. However, as plants extend their operating licenses to 60 and 80 years, justification for continued safe operation includes test and monitoring programs. These will become more important as the industry moves to condition based qualification programs. Cable test programs traditionally involve manual interventions to disconnect cables, perform one or several tests, then reconnect the systems, usually during refueling outages occurring only every 18 to 24 months. This poses an operational burden that can be minimized by online testing or periodic connection to a coupler that may remain on the cable of interest or be clamped onto the cable without de-termination. This work investigates the adaptation of a clamshell inductive current coupler for either frequency domain reflectometry or spread-spectrum time domain reflectometry. The reflectometry test instrument injects a broad-band chirp or pseudo-noise signal onto a cable conductor and monitors for a reflected signal indicative of an impedance change caused by a damage condition. The instrument maximum input signal levels are typically 10 to 30 volts or less and the instruments will be damaged if subjected to 60 Hz power line voltages of 110, 220, or 480 VAC. One commercial spread-spectrum time domain reflectometry system has circuitry suitable for voltages up to 1 kV, but typical reflectometry tests are performed on de-energized cables. The clamshell inductive coupler provides >60 dB of 60 Hz attenuation with less than 10 dB loss in the 1-500 MHz test bandwidth of interest. An energized cable was successfully tested up to 6.7 kVp-p and frequency response plots imply that the tests could be extended to 10 kV or higher energized levels.

36 MATERIALS SCIENCE↗