Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Examination”

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.

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

At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

The Effect of Velocity on the Extinction Behavior of a Diffusion Flame during Transient Depressurization

Current fire suppression plans for the International Space Station include the use of venting (depressurization) as a method for extinguishing a fire. Until recently this process had only been examined as part of a material flammability experiment performed on Skylab in the early 1970's. Due to the low initial pressure (0.35 Atm) and high oxygen concentration (65%), the Skylab experimental results are not applicable for understanding the effects of venting on a fire in a space station environment (21%O2, 1 Atm). Recent research examined the extinction behavior of a diffusion flame over a polymethyl methacrylate (PMMA) cylinder during a transient depressurization in low-gravity. The numerical model was used to examine extinction limits as a function of depressurization rate, forced flow velocity, and initial solid phase temperature. The experimental and numerically predicted extinction data indicated that as the solid phase temperature increased the pressure required to extinguish the flame decreased. The numerical model was also used to examine conditions not obtainable in the low-gravity experiments. From these simulations, a series of extinction boundaries were generated that showed a region of increased flammability existed at a forced flow of 10 cm/s. Analysis of these extinction boundaries indicated that they were quasi-steady in nature, and that the final extinction conditions were independent of the transient process. The velocity range in the previous study was limited and thus the results did not examine the effects of velocities less than 1 cm/s or greater than 20 cm/s. This study utilized low-gravity experiments performed on NASA's Reduced-gravity Research Aircraft Laboratory and numerical simulations to examine conditions applicable to the Space Station environment. This paper extends the analysis of the previous study to a comprehensive examination of the effect of increased velocity on extinction behavior and extinction limits during a transient depressurization in low-gravity. This is achieved by examining extinction data from buoyant (normal-gravity) and low-buoyant (low-gravity) depressurization. experiments, as well as from numerical predictions of flame behavior during depressurization in a non-buoyant (zero-gravity) environment.

Goldmeer, Jeffrey S.↗
NASA NTRS2014

Renewable Energy at NASA's Johnson Space Center

NASA's Johnson Space Center has implemented a great number of renewable energy systems. Renewable energy systems are necessary to research and implement if we humans are expected to continue to grow and thrive on this planet. These systems generate energy using renewable sources - water, wind, sun - things that we will not run out of. Johnson Space Center is helping to pave the way by installing and studying various renewable energy systems. The objective of this report will be to examine the completed renewable energy projects at NASA's Johnson Space Center for a time span of ten years, beginning in 2003 and ending in early 2014. This report will analyze the success of each project based on actual vs. projected savings and actual vs. projected efficiency. Additionally, both positive and negative experiences are documented so that lessons may be learned from past experiences. NASA is incorporating renewable energy wherever it can, including into buildings. According to the 2012 JSC Annual Sustainability Report, there are 321,660 square feet of green building space on JSC's campus. The two projects discussed here are major contributors to that statistic. These buildings were designed to meet various Leadership in Energy and Environmental Design (LEED) Certification criteria. LEED Certified buildings use 30 to 50 percent less energy and water compared to non-LEED buildings. The objectives of this project were to examine data from the renewable energy systems in two of the green buildings onsite - Building 12 and Building 20. In Building 12, data was examined from the solar photovoltaic arrays. In Building 20, data was examined from the solar water heater system. By examining the data from the two buildings, it could be determined if the renewable energy systems are operating efficiently. Objectives In Building 12, the data from the solar photovoltaic arrays shows that the system is continuously collecting energy from the sun, as shown by the graph below. Building 12 has two solar inverters, located on the second floor, that collected the data from the solar photovoltaic arrays. The data displayed here is the total energy produced by the system. These are cumulative amounts, so the last point on the graph shows all of the energy collected from the system since the start of its operation. The data shown here was manually collected from the solar inverters. However, the data is also automatically recorded through EBI. Through analysis of both sets of data it was determined that the EBI data was faulty. For example, from the manually collected data it can be determined that a total of 73 kWh of energy was collected between the dates of 1/16/2014 – 1/22/2014. The EBI data reports that approximately 17800 kWh of energy was collected during the same time frame. Not only does this exceed the time frame examined, but it also exceeds the total energy collected from the start of collection as recorded from the inverters. This leads to the belief that there is a malfunction with the automatic recording of the energy. In Building 20, data was examined from the solar water heater dating back many months and found that the pump for the solar water heater system was not operating properly, as exhibited in the graph shown below. The pump operates on a solar energy system, meaning that it collects energy throughout the day from the sun. Because of this, the system would stop operating shortly after the sun set because of a lack of sunlight. At that point, the graph should show a zero flow rate, but as exhibited in the graph below, that is not the case. It is clearly shown that the pump is continuously operating, even during the night. It was also observed that the majority of the time the pump would not turn on at all, despite good weather conditions. This led to the conclusion that the pump is malfunctioning, and needs to be examined and fixed.

McDowall, Lindsay↗
NASA NTRS1994

Experimental studies of transpiration cooling with shock interaction in hypersonic flow, part B

This report describes the result of experimental studies conducted to examine the effects of the impingement of an oblique shock on the flowfield and surface characteristics of a transpiration-cooled wall in turbulent hypersonic flow. The principal objective of this work was to determine whether the interaction between the oblique shock and the low-momentum region of the transpiration-cooled boundary layer created a highly distorted flowfield and resulted in a significant reduction in the cooling effectiveness of the transpiration-cooled surface. As a part of this program, we also sought to determine the effectiveness of transpiration cooling with nitrogen and helium injectants for a wide range of blowing rates under constant-pressure conditions in the absence of shock interaction. This experimental program was conducted in the Calspan 48-Inch Shock Tunnel at nominal Mach numbers of 6 and 8, for a Reynolds number of 7.5 x 10(exp 6). For these test conditions, we obtained fully turbulent boundary layers upstream of the interaction regions over the transpiration-cooled segment of the flat plate. The experimental program was conducted in two phases. In the first phase, we examined the effects of mass-addition level and coolant properties on the cooling effectiveness of transpiration-cooled surfaces in the absence of shock interaction. In the second phase of the program, we examined the effects of oblique shock impingement on the flowfield and surface characteristics of a transpiration-cooled surface. The studies were conducted for a range of shock strengths with nitrogen and helium coolants to examine how the distribution of heat transfer and pressure and the characteristics of the flowfield in the interaction region varied with shock strength and the level of mass addition from the transpiration-cooled section of the model. The effects of the distribution of the blowing rate along the interaction regions were also examined for a range of blowing rates through the transpiration-cooled panels. The regions of shockwave/boundary layer interaction examined in these studies were induced by oblique shocks generated with a sharp, flat plate, inclined to the freestream at angles of 5 degrees, 7.5 degrees, and 10 degrees. It was found that, in the absence of an incident shock, transpiration cooling was a very effective method for reducing both the heat transfer and the skin friction loads on the surface. The helium coolant was found to be significantly more effective than nitrogen, because of its low molecular weight and high specific heat. The studies of shock-wave/transpiration-cooled surface interaction demonstrated that the interaction region between the incident shock and the low-momentum transpiration-cooled boundary layer did not result in a significant increase in the size of attached or separated interaction regions, and did not result in significant flowfield distortions above the interaction region. The increase in heating downstream of the shock-impingement point could easily be reduced to the values without shock impingement by a relatively small increase in the transpiration cooling in this region. Surprisingly, this increase in cooling rate did not result in a significant increase in size of the region ahead of the incident shock or create a significantly enlarged interaction region with a resultant increase in the distortion level in the inviscid flow. Thus, transpiration cooling appears to be a very effective technique to cool the internal surfaces of scramjet engines, where shocks in the engine would induce large local increases in wall heating and create viscous/inviscid interactions that could significantly disturb the smooth flow through the combustor. However, if hydrogen is used as the coolant, burning upstream of shock impingement might result in localized hot spots. Clearly, further research is needed in this area.

Holden, Michael S.↗
NASA NTRS1998

The Effect of Interruptions on Part 121 Air Carrier Operations

The primary purpose of this study was to determine the relative priorities of various events and activities by examining the probability that a given activity was interrupted by a given event. The analysis will begin by providing frequency of interruption data by crew position (captain versus first officer) and event type. Any differences in the pattern of interruptions between the first officers and the captains will be explored and interpreted in terms of standard operating procedures. Subsequent data analyses will focus on comparing the frequency of interruptions for different types of activities and for the same activities under normal versus emergency conditions. Briefings and checklists will receive particular attention. The frequency with which specific activities are interrupted under multiple- versus single-task conditions also will be examined; because the majority of multiple-task data were obtained under laboratory conditions, LOFT-type tapes offer a unique opportunity to examine concurrent task performance under 'real-world' conditions. A second purpose of this study is to examine the effects of the interruptions on performance. More specifically, when possible, the time to resume specific activities will be compared to determine if pilots are slower to resume certain types of activities. Errors in resumption or failures to resume specific activities will be noted and any patterns in these errors will be identified. Again, particular attention will be given to the effects of interruptions on the completion of checklists and briefings. Other types of errors and missed events (i.e., the crew should have responded to the event but did not) will be examined. Any methodology using interruptions to examine task prioritization must be able to identify when an interruption has occurred and describe the ongoing activities that were interrupted. Both of these methodological problems are discussed In detail in the following section,

Damos, Diane L.↗
NASA NTRS1998

Thermomechanical Fatigue Durability of T650-35/PMR-15 Sheet Molding Compound

Although polyimide based composites have been used for many years in a wide variety of elevated temperature applications, very little work has been done to examine the durability and damage behavior under more prototypical thermomechanical fatigue (TMF) loadings. Synergistic effects resulting from simultaneous temperature and load cycling can potentially lead to enhanced, if not unique, damage modes and contribute to a number of nonlinear deformation responses. The goal of this research was to examine the effects of a TMF loading spectrum, representative of a gas turbine engine compressor application, on a polyimide sheet molding compound (SMC). High performance SMCs present alternatives to prepreg forms with great potential for low cost component production through less labor intensive, more easily automated manufacturing. To examine the issues involved with TMF, a detailed experimental investigation was conducted to characterize the durability of a T650-35/PMR-15 SMC subjected to TMF mission cycle loadings. Fatigue damage progression was tracked through macroscopic deformation and elastic stiffness. Additional properties, such as the glass transition temperature (T(sub g) and dynamic mechanical properties were examined. The fiber distribution orientation was also characterized through a detailed quantitative image analysis. Damage tolerance was quantified on the basis of residual static tensile properties after a prescribed number of TMF missions. Detailed microstructural examinations were conducted using optical and scanning electron microscopy to characterize the local damage. The imposed baseline TMF missions had only a modest impact on inducing fatigue damage with no statistically significant degradation occurring in the measured macroscopic properties. Microstructural damage was, however, observed subsequent to 100 h of TMF cycling which consisted primarily of fiber debonding and transverse cracking local to predominantly transverse fiber bundles. The TMF loadings did introduce creep related effects (strain accumulation) which led to rupture in some of the more aggressive stress scenarios examined. In some cases this creep behavior occurred at temperatures in excess of 150 C below commonly cited values for T(sub g). Thermomechanical exploratory creep tests revealed that the SMC was subject to time dependent deformation at stress/temperature thresholds of 150 MPa/230 C and 170 MPa/180 C.

Castelli, Michael G.↗
NASA NTRS1998

Residual Stresses Modeled in Thermal Barrier Coatings

Thermal barrier coating (TBC) applications continue to increase as the need for greater engine efficiency in aircraft and land-based gas turbines increases. However, durability and reliability issues limit the benefits that can be derived from TBC's. A thorough understanding of the mechanisms that cause TBC failure is a key to increasing, as well as predicting, TBC durability. Oxidation of the bond coat has been repeatedly identified as one of the major factors affecting the durability of the ceramic top coat during service. However, the mechanisms by which oxidation facilitates TBC failure are poorly understood and require further characterization. In addition, researchers have suspected that other bond coat and top coat factors might influence TBC thermal fatigue life, both separately and through interactions with the mechanism of oxidation. These other factors include the bond coat coefficient of thermal expansion, the bond coat roughness, and the creep behavior of both the ceramic and bond coat layers. Although it is difficult to design an experiment to examine these factors unambiguously, it is possible to design a computer modeling "experiment" to examine the action and interaction of these factors, as well as to determine failure drivers for TBC's. Previous computer models have examined some of these factors separately to determine their effect on coating residual stresses, but none have examined all the factors concurrently. The purpose of this research, which was performed at DCT, Inc., in contract with the NASA Lewis Research Center, was to develop an inclusive finite element model to characterize the effects of oxidation on the residual stresses within the TBC system during thermal cycling as well as to examine the interaction of oxidation with the other factors affecting TBC life. The plasma sprayed, two-layer thermal barrier coating that was modeled incorporated a superalloy substrate, a NiCrAlY bond coat, and a ZrO2-8 wt % Y2O3 ceramic top coat. We examined the effect on stress during burner rig thermal cycling of the following independent variables: creep in the bond coat and top coat, oxidation, bond coat coefficient of thermal expansion, number of thermal cycles, and interfacial roughness. All these factors were suspected of influencing TBC failure. The model showed that all the material properties studied had a significant effect on the coating's residual stresses if the interface of the bond coat was rough. Bond coat expansion, bond coat oxidation, and bond coat creep had the highest effect on coating stresses, and these were highly interactive. The model also showed that the mechanism of stress generation during thermal cycling changed with the number of thermal cycles. Bond coat and top coat creep dominated stress generation during early thermal cycles, greatly increasing delamination stresses at the peaks of the bond coat. Therefore, creep is the prime driver for delamination cracking early in life, but cracking is limited to the bond coat peak region. Oxidation of the bond coat, on the other hand, tended to dominate stress generation during later cycles by greatly increasing delamination stresses over bond coat valleys. These results indicate that oxidation is the driver for the continued cracking necessary to cause ceramic layer spallation.

Freborg, A. M.↗