SEARCH · Engineering Papers

Results for “Pressure Core”

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 1,189 records · Page 66

All sources NASA NTRS DOE OSTI

NASA NTRS2004

Further Progress in Noise Source Identification in High Speed Jets via Causality Principle

To locate noise sources in high-speed jets, the sound pressure fluctuations p/, measured at far field locations, were correlated with each of density p, axial velocity u, radial velocity v, puu and pvv fluctuations measured from various points in fully expanded, unheated plumes of Mach number 0.95, 1.4 and 1.8. The velocity and density fluctuations were measured simultaneously using a recently developed, non-intrusive, point measurement technique based on molecular Rayleigh scattering (Seasholtz, Panda, and Elam, AIAA Paper 2002-0827). The technique uses a continuous wave, narrow line-width laser, Fabry-Perot interferometer and photon counting electronics. The far field sound pressure fluctuations at 30 to the jet axis provided the highest correlation coefficients with all flow variables. The correlation coefficients decreased sharply with increased microphone polar angle, and beyond about 60 all correlation mostly fell below the experimental noise floor. Among all correlations < puu; p/> showed the highest values. Interestingly, , in all respects, were very similar to . The and correlations with 90deg microphone fell below the noise floor. By moving the laser probe at various locations in the jet it was found that the strongest noise source lies downstream of the end of the potential core and extends many diameters beyond. Correlation measurement from the lip shear layer showed a Mach number dependency. While significant correlations were measured in Mach 1.8 jet, values were mostly below the noise floor for subsonic Mach 0.95 jet. Various additional analyses showed that fluctuations from large organized structures mostly contributed to the measured correlation, while that from small scale structures fell below the noise floor.

Panda, J.↗

NASA NTRS2002

Large Eddy Simulation of Cryogenic Injection Processes at Supercritical Pressure

This paper highlights results from the first of a series of hierarchical simulations aimed at assessing the modeling requirements for application of the large eddy simulation technique to cryogenic injection and combustion processes in liquid rocket engines. The focus is on liquid-oxygen-hydrogen coaxial injectors at a condition where the liquid-oxygen is injected at a subcritical temperature into a supercritical environment. For this situation a diffusion dominated mode of combustion occurs in the presence of exceedingly large thermophysical property gradients. Though continuous, these gradients approach the behavior of a contact discontinuity. Significant real gas effects and transport anomalies coexist locally in colder regions of the flow, with ideal gas and transport characteristics occurring within the flame zone. The current focal point is on the interfacial region between the liquid-oxygen core and the coaxial hydrogen jet where the flame anchors itself.

Oefelein, Joseph C.↗

NASA NTRS2002

Large Eddy Simulation of Cryogenic Injection Processes at Supercritical Pressure

Oefelein, Joseph C.↗

NASA NTRS1979

Quasi-periodic structure of a turbulent jet

The instantaneous near field pressure fluctuations of an axisymmetric subsonic jet were measured by using a longitudinal and an azimuthal microphone arrays in order to qualitatively determine the behaviors of the quasi-periodic structure within the flow. Statistical analysis is used to explain the characteristic of the pressure signals. In addition to the information obtained by forming the power spectral density, auto- and cross-correlation functions, two types of signals are extracted through a conditional probability analysis to represent the quasi-periodic and the random fine structures within the turbulent jet. The quasi-periodic structure first appears as a rolling up of the mixing layer flow within one nozzle diameter downstream of the exit, then becomes fully developed at approximately 3 nozzle diameters downstream with a preferred Strouhal number range 0.3-0.4, and finally disappears beyond the end of potential core. This behavior is also reflected in the variation of the convection velocity.

Maestrello, L.↗

NASA NTRS1975

Cold-air annular-cascade investigation of aerodynamic performance of core-engine-cooled turbine vanes. 1: Solid-vane performance and facility description

The aerodynamic performance of a solid (uncooled) version of a core engine cooled stator vane was experimentally determined in a full-annular cascade, where three-dimensional effects could be obtained. The solid vane, which serves as a basis for comparison with subsequent cooled tests, was tested over a range of aftermixed critical velocity ratios of 0.57 to 0.90. Overall vane aftermixed efficiencies were obtained over this critical velocity ratio range and compared with results from a two-dimensional cascade. The variation in vane efficiency and aftermixed flow conditions with circumferential and radial position were obtained and compared with design values. Vane surface static-pressure distributions were also measured and compared with theoretical results.

Goldman, L. J.↗

NASA NTRS2004

Thermal Load Considerations for Detonative Combustion-Based Gas Turbine Engines

An analysis was conducted to assess methods for, and performance implications of, cooling the passages (tubes) of a pulse detonation-based combustor conceptually installed in the core of a gas turbine engine typical of regional aircraft. Temperature-limited material stress criteria were developed from common-sense engineering practice, and available material properties. Validated, one-dimensional, numerical simulations were then used to explore a variety of cooling methods and establish whether or not they met the established criteria. Simulation output data from successful schemes were averaged and used in a cycle-deck engine simulation in order to assess the impact of the cooling method on overall performance. Results were compared to both a baseline engine equipped with a constant-pressure combustor and to one equipped with an idealized detonative combustor. Major findings indicate that thermal loads in these devices are large, but potentially manageable. However, the impact on performance can be substantial. Nearly one half of the ideally possible specific fuel consumption (SFC) reduction is lost due to cooling of the tubes. Details of the analysis are described, limitations are presented, and implications are discussed.

Paxson, Daniel E.↗

NASA NTRS2005

Space Shuttle Hot Cabin Emergency Responses

Methods: Human thermal tolerance, countermeasures, and thermal model data were reviewed and compared to existing shuttle ECS failure temperature and humidity profiles for each failure mode. Increases in core temperature associated with cognitive impairment was identified, as was metabolic heat generation of crewmembers, temperature monitoring, and communication capabilities after partial power-down and other limiting factors. Orbiter landing strategies and a hydration and salt replacement protocol were developed to put wheels on deck in each failure mode prior to development of significant cognitive impairment or collapse of crewmembers. Thermal tradeoffs for use of the Advanced Crew Escape Suit (ACES), Liquid Cooling Garment, integrated G-suit and Quick Don Mask were examined. candidate solutions involved trade-offs or conflicts with cabin oxygen partial pressure limits, system power-downs to limit heat generation, risks of alternate and emergency landing sites or compromise of Mode V-VIII scenarios. Results: Rehydration and minimized cabin workloads are required in all failure modes. Temperature/humidity profiles increase rapidly in two failure modes, and deorbit is recommended without the ACES, ICU and g-suit. This latter configuration limits several shuttle approach and landing escape modes and requires communication modifications. Additional data requirements were identified and engineering simulations were recommended to develop more current shuttle temperature and humidity profiles. Discussion: After failure of the shuttle ECS, there is insufficient cooling capacity of the ACES to protect crewmembers from rising cabin temperature and humidity. The LCG is inadequate for cabin temperatures above 76 F. Current shuttle future life policy makes it unlikely that major engineering upgrades necessary to address this problem will occur.

Stepaniak, P.↗

NASA NTRSDate not supplied

Thermal Protection System P50 Cork Environments and Response due to Radiative Heating

Space Launch System (SLS) experienced deflagration of the acreage of the Core Stage base heat shield during the Green Run hot-fire test campaigns and Artemis I flight. The burning products from the base heat shield during Green Run hot-fire test operation led to concerns in aerothermal environments and thermal protection system (TPS) performance prior to Artemis I flight. This work documents a highly controlled ground test within the NASA Marshall Space Flight Center’s Nonmetallic Materials Branch thermal vacuum chamber (TVC) and investigates the P50 cork heat transfer environments and thermal protection system (TPS) response due to sensitivity changes in radiative heat rates, ambient pressure, air entrainment mass flow rates, test gas and TPS sample types. An SLS ascent ambient pressure profile was also simulated within the TVC facility. This test data enabled the efforts toward the Artemis I SLS post-flight reconstruction and initial assessment of flight TPS performance. A ground test program was developed to gain an in-depth understanding of the cork combustion dynamics and TPS response due to the SLS launch vehicle flight ascent environments.

thermal protection system↗

NASA NTRS1981

The distribution and morphology of X-ray-emitting gas in the core of the Perseus cluster

An unresolved source has been found coincident with the nucleus of NGC 1275 in a high-resolution X-ray image of the core of the Perseus cluster. Absorption in the optical features at high velocity with respect to NGC 1275, which are thought to be associated with a foreground galaxy, does not produce any detectable X-ray absorption. The emission tends to become asymmetric in the presence of the lower-velocity filaments, but no obvious, detailed correlation is found between X-ray enhancements and individual filaments. Deprojection of surface brightness to yield temperature and density profiles of the intracluster gas shows results consistent with a quasi-hydrostatic radiative accretion flow onto NGC 1275, and the pressure-driven mass inflow onto the central galaxy is then 200-400 solar masses/yr. The possibility of a problem in the relation of line-of-sight velocity dispersion to cluster gravitational mass is confirmed.

Fabian, A. C.↗

NASA NTRS2012

Materials Selection for Aerospace Systems

A systematic design-oriented, five-step approach to material selection is described: 1) establishing design requirements, 2) material screening, 3) ranking, 4) researching specific candidates and 5) applying specific cultural constraints to the selection process. At the core of this approach is the definition performance indices (i.e., particular combinations of material properties that embody the performance of a given component) in conjunction with material property charts. These material selection charts, which plot one property against another, are introduced and shown to provide a powerful graphical environment wherein one can apply and analyze quantitative selection criteria, such as those captured in performance indices, and make trade-offs between conflicting objectives. Finding a material with a high value of these indices maximizes the performance of the component. Two specific examples pertaining to aerospace (engine blades and pressure vessels) are examined, both at room temperature and elevated temperature (where time-dependent effects are important) to demonstrate the methodology. The discussion then turns to engineered/hybrid materials and how these can be effectively tailored to fill in holes in the material property space, so as to enable innovation and increases in performance as compared to monolithic materials. Finally, a brief discussion is presented on managing the data needed for materials selection, including collection, analysis, deployment, and maintenance issues.

Arnold, Steven M.↗

NASA NTRSDate not supplied

Cloud-Type Mean Cloud Properties and Associated Cloud Radiative Effects in the Tropical “Chimney” Zones Using 20 Years High-Resolution CERES Satellite Data

It has been well known that convection tends to be more intense over land than over ocean and continental convection generally contains wider cores that are protected from entrainment than their oceanic counterparts. How does this difference in convective intensity impact the rest of cloud types and associated cloud radiative effects (CREs)? We select five regions in the tropical “chimney” zones, with two regions over land (Africa and Amazon) and three regions over ocean (eastern and western Pacific, and Atlantic) to understand the differences in the cloud-type mean cloud properties and associated CREs using 20-years high-resolution (2x2 km2) CERES satellite data. The cloud types are based upon the ISCCP classification using the joint cloud-top pressure and cloud optical depth distribution. These five regions are compared to the entire tropics (25°S to 25°N). First, we compare the frequencies of occurrence of cloud types among the regions. Compared to the entire tropics, the “chimney” zones are cloudier, particularly, for cloud types with moderate cloud optical depths in the middle and upper troposphere. Except for the eastern Pacific region, the low-level cloud types are less abundant over land (due to higher boundary layers) and ocean (due to weaker lower-tropospheric subsidence). Over Africa, upper-level clouds are scarcer, due perhaps to weak production of convective anvils related to the drier atmosphere. Second, liquid water path (LWP) and ice water path (IWP) are compared among the regions. Compared to the entire tropics, mean LWPs for moderate cloud optical depths are higher for oceanic regions but lower for Africa while they are slightly lower in the lower troposphere but slightly higher in the middle troposphere for Amazon. Not surprisingly, mean IWPs are higher over land than over ocean, which is directly related to the difference in convective intensity. That is, the explanations to this result are the relatively weak convective intensity over the eastern Pacific and the abundance of anvil clouds over the western Pacific. Both reduce the mean IWPs. The CRE results are still being analyzed because the totally-clear grids (1° x 1°) of the CERES data product should be removed before taking a regional mean of clear-sky fluxes, which cause the wrong signs of CREs for a few cloud types.

cloud radiative effects↗

NASA NTRS1973

Surface magnetometer experiments: Internal lunar properties

Magnetic fields have been measured on the lunar surface at the Apollo 12, 14, 15, and 16 landing sites. The remanent field values at these sites are respectively 38 gammas, 103 gammas (maximum), 3 gammas, and 327 gammas. Simultaneous magnetic field and solar plasma pressure measurements show that the remanent fields at the Apollo 12 and 16 sites are compressed and that the scale size of the Apollo 16 remanent field is 5 or = L 100 km. The global eddy current fields, induced by magnetic step transients in the solar wind, were analyzed to calculate an electrical conductivity profile. From nightside data it was found that deeper than 170 km into the moon, the conductivity rises from 0.0003 mhos/m to 0.01 mhos/m at 1000 km depth. Analysis of dayside transient data using a spherically symmetric two-layer model yields a homogeneous conducting core of radios 0.9 R and conductivity sigma = 0.001 mhos/m, surrounded by a nonconducting shell of thickness 0.1 R. This result is in agreement with a nonconducting profile determined from nightside data. The conductivity profile is used to calculate the temperature for an assumed lunar material of peridotite. In an outer layer the temperature rises to 850 to 1050 K, after which it gradually increases to 1200 to 1500 K at a depth of approximately 1000 km.

Dyal, P.↗

NASA NTRS1986

Compound cycle engine program

The Compound Cycle Engine (CCE) is a highly turbocharged, power compounded power plant which combines the lightweight pressure rise capability of a gas turbine with the high efficiency of a diesel. When optimized for a rotorcraft, the CCE will reduce fuel burned for a typical 2 hr (plus 30 min reserve) mission by 30 to 40 percent when compared to a conventional advanced technology gas turbine. The CCE can provide a 50 percent increase in range-payload product on this mission. A program to establish the technology base for a Compound Cycle Engine is presented. The goal of this program is to research and develop those technologies which are barriers to demonstrating a multicylinder diesel core in the early 1990's. The major activity underway is a three-phased contract with the Garrett Turbine Engine Company to perform: (1) a light helicopter feasibility study, (2) component technology development, and (3) lubricant and material research and development. Other related activities are also presented.

Bobula, G. A.↗

NASA NTRS1987

Compound cycle engine program

The Compound Cycle Engine (CCE) is a highly turbocharged, power compounded power plant which combines the lightweight pressure rise capability of a gas turbine with the high efficiency of a diesel. When optimized for a rotorcraft, the CCE will reduce fuel burn for a typical 2 hr (plus 30 min reserve) mission by 30 to 40 percent when compared to a conventional advanced technology gas turbine. The CCE can provide a 50 percent increase in range-payload product on this mission. A program to establish the technology base for a Compound Cycle Engine is presented. The goal of this program is to research and develop those technologies which are barriers to demonstrating a multicylinder diesel core in the early 1990's. The major activity underway is a three-phased contract with the Garrett Turbine Engine Company to perform: (1) a light helicopter feasibility study, (2) component technology development, and (3) lubricant and material research and development. Other related activities are also presented.

Bobula, G. A.↗

NASA NTRS1992

Vortex breakdown incipience: Theoretical considerations

The sensitivity of the onset and the location of vortex breakdowns in concentrated vortex cores, and the pronounced tendency of the breakdowns to migrate upstream have been characteristic observations of experimental investigations; they have also been features of numerical simulations and led to questions about the validity of these simulations. This behavior seems to be inconsistent with the strong time-like axial evolution of the flow, as expressed explicitly, for example, by the quasi-cylindrical approximate equations for this flow. An order-of-magnitude analysis of the equations of motion near breakdown leads to a modified set of governing equations, analysis of which demonstrates that the interplay between radial inertial, pressure, and viscous forces gives an elliptic character to these concentrated swirling flows. Analytical, asymptotic, and numerical solutions of a simplified non-linear equation are presented; these qualitatively exhibit the features of vortex onset and location noted above.

Berger, Stanley A.↗

NASA NTRS2008

Intelligent Engine Systems: Thermal Management and Advanced Cooling

The objective of the Advanced Turbine Cooling and Thermal Management program is to develop intelligent control and distribution methods for turbine cooling, while achieving a reduction in total cooling flow and assuring acceptable turbine component safety and reliability. The program also will develop embedded sensor technologies and cooling system models for real-time engine diagnostics and health management. Both active and passive control strategies will be investigated that include the capability of intelligent modulation of flow quantities, pressures, and temperatures both within the supply system and at the turbine component level. Thermal management system concepts were studied, with a goal of reducing HPT blade cooling air supply temperature. An assessment will be made of the use of this air by the active clearance control system as well. Turbine component cooling designs incorporating advanced, high-effectiveness cooling features, will be evaluated. Turbine cooling flow control concepts will be studied at the cooling system level and the component level. Specific cooling features or sub-elements of an advanced HPT blade cooling design will be downselected for core fabrication and casting demonstrations.

Bergholz, Robert↗

NASA NTRS1976

Experimental evaluation of outer planets probe thermal insulation concepts

An experimental program was conducted to evaluate various thermal insulation concepts for use in the Outer Planets Probe (OPP) during entry and descent into the atmospheres of Jupiter, Saturn, and Uranus. Phenolic fiberglass honeycomb specimens representative of the OPP structure were packed and tested with various fillers: Thermal conductivity measurements were made over a temperature range of 300 K to 483 K and pressures from vacuum up to 10 atmospheres in helium and nitrogen gas environments. The conductivity results could not be fully explained so new test specimens were designed with improved venting characteristics, and tested to determine the validity of the original data. All of the conductivity data showed results that were substantially higher than expected. The original test data in helium were lower than the data from the redesigned specimens, probably due to inadequate venting of nitrogen gas from the original specimens. The thermal conductivity test results show only a marginal improvement in probe thermal protection performance for a filled honeycomb core compared to an unfilled core. In addition, flatwise tension tests showed a severe bond strength degradation due to the inclusion of either the powder or foam fillers. In view of these results, it is recommended that the baseline OPP design utilize an unfilled core.

Grote, M. G.↗

NASA NTRS1980

Flow field and acoustic properties of a Mach number 0.9 jet at a low Reynolds number

An experimental study of the flow field and acoustic properties of a low Reynolds number M = 0.9 jet has been performed in a low pressure anechoic test chamber. The mean flow field was surveyed with a conventional pitot pressure probe and flow fluctuations were detected with a normal hot wire probe. Also, condenser microphone measurements were made in the acoustic field. The flow fluctuations within the jet were found to be dominated initially by a relatively discrete, large-scale, wave-like instability centered around a Strouhal number of 0.44. The axial wavelength of this instability was determined to be 1.45 jet diameters and its azimuthal character includes the n = 0 and n = plus or minus 1 modes. The growth of this instability coupled with its nonlinear breakdown are major contributors to the termination of the potential core region of the jet. The acoustic field of the jet, in contrast to the flow field, has a broad frequency spectrum with a peak amplitude near a Strouhal number of St = 0.2. The results indicate that a nonlinear mechanism involving the large-scale flow instability is responsible for a dominant portion of the noise generated from this jet.

Stromberg, J. L.↗