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At least 289 records · Page 16

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NASA NTRS2014

Noise from Aft Deck Exhaust Nozzles: Differences in Experimental Embodiments

Two embodiments of a rectangular nozzle on an aft deck are compared. In one embodiment the lower lip of the nozzle was extended with the sidewalls becoming triangles. In a second embodiment a rectangular nozzle was fitted with a surface that fit flush to the lower lip and extended outward from the sides of the nozzle, approximating a semi-infinite plane. For the purpose of scale-model testing, making the aft deck an integral part of the nozzle is possible for relatively short deck lengths, but a separate plate model is more flexible, accounts for the expanse of deck to the sides of the nozzle, and allows the nozzle to stand off from the deck. Both embodiments were tested and acoustic far-field results were compared. In both embodiments the extended deck introduces a new noise source, but the amplitude of the new source was dependent upon the span (cross-stream dimension) of the aft deck. The noise increased with deck length (streamwise dimension), and in the case of the beveled nozzle it increased with increasing aspect ratio. In previous studies of slot jets in wings it was noted that the increased noise from the extended aft deck appears as a dipole at the aft deck trailing edge, an acoustic source type with different dependence on velocity than jet mixing noise. The extraneous noise produced by the aft deck in the present studies also shows this behavior both in directivity and in velocity scaling.

Bridges, James E.↗

NASA NTRS2014

Noise from Aft Deck Exhaust Nozzles: Differences in Experimental Embodiments

Bridges, James↗

NASA NTRS2015

Inward-Turning Streamline-Traced Inlet Design Method for Low-Boom, Low-Drag Applications

A new design method for inward-turning, streamline-traced inlets is presented. Resulting designs are intended for moderate supersonic, low-drag, low-boom applications such as that required for NASA's proposed low-boom flight demonstration aircraft. A critical feature of these designs is the internal cowl lip angle that allows for little or no flow turning on the outer nacelle. Present methods using conical-flow Busemann parent flowfields have simply truncated, or otherwise modified the stream-traced contours to include this internal cowl angle. Such modifications disrupt the parent flowfield, reducing inlet performance and flow uniformity. The method presented herein merges a conical flowfield that includes a leading shock with a truncated Busemann flowfield in a manner that minimizes unwanted interactions. A leading internal cowl angle is now inherent in the parent flowfield, and inlet contours traced from this flowfield retain its high performance and good flow uniformity. CFD analysis of a candidate inlet design is presented that verifies the design technique, and reveals a starting issue with the basic geometry. A minor modification to the cowl lip region is shown to eliminate this phenomenon, thereby allowing starting and smooth transition to sub-critical operation as back-pressure is increased. An inlet critical-point total pressure recovery of 96 is achieved based on CFD results for a Mach 1.7 freestream design. Correction for boundary-layer displacement thickness, and sizing for a given engine airflow requirement are also discussed.

low sonic boom↗

NASA NTRS2015

Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly proposed for embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side ('bevel') did produce up to 3dB more noise in all directions, while extending the lip on the narrow side ('slant') produced up to 2dB more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron ('notch') produced up to 2dB increase in the noise. Having internal walls ('septae') within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

Noise↗

NASA NTRS2015

Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly found in embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side (bevel) did produce up to 3 decibels more noise in all directions, while extending the lip on the narrow side (slant) produced up to 2 decibels more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron (notch) produced up to 2decibels increase in the noise. Having internal walls (septae) within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed electric propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

Noise↗

NASA NTRS2017

Off-Design Performance of a Streamline-Traced, External-Compression Supersonic Inlet

A computational study was performed to explore the aerodynamic performance of a streamline-traced, external-compression inlet designed for Mach 1.664 at off-design conditions of freestream Mach number, angle-of-attack, and angle-of-sideslip. Serious degradation of the inlet performance occurred for negative angles-of-attack and angles-of-sideslip greater than 3 degrees. At low subsonic speeds, the swept leading edges of the inlet created a pair of vortices that propagated to the engine face. Increasing the bluntness of the cowl lip showed no real improvement in the inlet performance at the low speeds, but did improve the inlet performance at the design conditions. Reducing the inlet flow rate improved the inlet performance, but at the likely expense of reduced thrust of the propulsion system. Deforming the cowl lip for low-speed operation of the inlet increased the inlet capture area and improved the inlet performance.

distortion↗

NASA NTRS2018

Experimental and Computational Study of Tones Occurring with a Coaxial Nozzle

The source of audible tones occurring with a coaxial nozzle in a range of low Mach numbers is explored experimentally as well as computationally. The hardware is comprised of an inner and an outer nozzle, without a center-body, that are held together by a set of four struts. With increasing jet Mach number (M(sub j)), first a tone occurred at about 2550 Hz around M(sub j)=0.06. At higher values of M(sub j) a tone at 5200 Hz dominated the noise spectra. The corresponding nondimensional frequency, based on effective thickness of the inner nozzle lip and jet exit velocity, turned out to be about 0.2, a value characteristic of Karmann vortex shedding. Thus, vortex shedding from the inner nozzle lip could be linked to the tones. From a comparison of the acoustic wavelengths and the nozzle dimensions, it was inferred that the vortex shedding excited a one-quarter-wave resonance within the divergent section of either the inner nozzle or the outer nozzle. This led to the generation of the sharp tones.

nozzle↗

NASA NTRS2017

Jet Noise Prediction Using Hybrid RANS/LES with Structured Overset Grids

Hybrid RANS/LES simulations using the structured overset grid approach and a low dissipation finite-difference method within the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are presented for jet noise prediction. The simulations are part of a validation effort to demonstrate jet noise prediction capability, to assess noise characteristics of next generation quiet supersonic commercial jets. Results are compared with experimental data acquired in the Small Hot Jet Acoustic Rig in the Aeroacoustic Propulsion Laboratory at NASA Glenn Research Center. Details of the structured overset grids, numerical discretization, and turbulence model are provided. Near-field comparisons to PIV data and far-field comparisons to microphone data are discussed. Excellent agreement of time-averaged mean quantities along the jet center-line and lip-line are obtained. Good agreement with root-mean-squared (RMS) quantities along the jet center-line are also obtained. An over prediction of lip-line RMS at the nozzle exit is observed leading to a small over-prediction of side-line far-field noise (less than 2 dB). Good agreement with far-field noise in the Mach wave radiation directions is achieved.

Housman, Jeffrey A.↗

NASA NTRS2019

Scaling Evaluation of Ice-Crystal Icing on a Modern Turbofan Engine in PSL Using the COMDES-MELT Code

This paper presents preliminary ice-crystal icing (ICI) altitude scaling evaluation results of a Honeywell Uncertified Research Engine (HURE) that was tested in the NASA Glenn Research Center Propulsion Systems Laboratory (PSL) during January of 2018. This engine geometry features a hidden core design to keep the core less exposed. The engine was fitted with internal video cameras to observe various ice buildup processes at multiple selected locations within the engine core flow path covering the fan stator, the splitter-lip/shroud/strut, and the high pressure compressor (HPC) variable inlet guide vane (IGV) regions. The potential ice accretion risk was pre-determined to occur by using NASA’s in-house 1D Engine Icing Risk assessment code, COMDES-MELT. The code was successful in predicting the risk of ice accretion in adiabatic regions like the fan-stator of the HURE at specific engine operating points. However at several operating points during the test, liquid water was observed running along the shroud toward the variable IGV of the HPC regions with an air temperature well below freezing, thus no particle melting could have occurred due to heating from the air alone. It was reasoned that other sources of heat were present in that region. To account for these heat sources the inlet total temperature was adjusted to give a wet bulb temperature of 24 F below the standard minimum wet bulb temperature of 492 R to allow ice to accrete in the splitter-lip/shroud/strut region, which was determined from a reference case where hard ice was observed in that region. With that adjustment the COMDES-MELT code was successful in providing operating points where there was a risk of ice accretion during the test campaign. In addition to calculating possible conditions at different selected lower altitudes, simulations were run to determine potential inlet conditions that could lead to ice-crystal accretion along the prescribed stations where the cameras were available. From there, scaled test conditions were determined by best matching the following three icing related parameters of the reference condition: (1) the local air total wet bulb temperature, (2) the local ice crystal cloud melt ratio and (3) the engine fan face ice/water to air mass flux ratio of the ice crystal cloud. Instantaneous images taken from the time-lapsed movies of ice buildup were used along with the relevant thermodynamic data of air, water vapor and local icing condition to help evaluate how closely the proposed altitude scaling method could be used in ground based test facility to duplicate selected reference ICI features observed at specific location inside this engine at different scale altitudes. Discussions on observed limitation for engine icing scaling application from this test campaign and needed improvement are provided. A scaling test procedure to help identify potential ICI risk conditions and possible ice accretion locations of a new turbofan engine is evaluated in PSL.

Engine Testing in PSL↗

NASA NTRS2021

Ice-Crystal Icing Investigation on a Honeywell Uncertified Research Engine in an Altitude Simulation Icing Facility

A Honeywell Uncertified Research Engine was exposed to various ice-crystal conditions in the NASA Propulsion Systems Laboratory (PSL). Simulations using NASA's one-dimensional (1D) Icing Risk Analysis tool were used to determine potential inlet conditions that could lead to ice-crystal accretion along the inlet of the core flowpath and into the high-pressure compressor. Baseline conditions were established, and parameters were varied to observe accretion characteristics. Data were acquired at altitudes varying from 5 kft to 45 kft, at nominal ice particle median volumetric diameters from 20 µm to 100 µm, and total water contents of 1 g/m3 to 12 g/m3. Metal temperatures were acquired for the inlet guide vane and vane stators 1–2. In situ measurements of the particle size distribution were acquired upstream and downstream of the engine fan face in order to study particle breakup behavior. Cameras were installed in the engine to capture ice accretions at the leading edge of the fan stator, splitter lip, and inlet guide vane. The goal of this study was to understand the key parameters of accretion, acquire particle breakup data aft of the fan, and generate a unique icing dataset for model development. Significant particle breakup downstream of the fan in the bypass was observed. The metal temperatures on the inlet guide vanes (IGVs) and stators show a temperature increase with increasing particle size. Accretion behavior at the fan stator and splitter lip across was very similar. However, accretion decreased with increasing particle size at the IGVs.

Ashlie B. Flegel↗

NASA NTRS2021

Time Resolved Particle Image Velocimetry in Nozzle Flow

Temporally resolved particle image velocimetry (TR-PIV) is the newest and most exciting tool recently developed to support our continuing efforts to characterize and improve our understanding of the decay of turbulence in jet flows—a critical element for understanding the acoustic properties of the flow. A new TR-PIV system has been developed at the NASA Glenn Research Center which is capable of acquiring planar PIV image frame pairs at up to 25 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered six nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centred along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space–time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.

Temporally Resolved Particle Image Velocimetry↗

NASA NTRSDate not supplied

Heat-death by volcano - how Venus went rogue?

The idea of a habitable Venus epoch has gained traction in recent years via 1-D and 3-D General Circulation Modeling (GCM) efforts [1,2,3]. Although recent work has supported an alternative permanent hot and dry scenario [4]. However, the habitable scenario presents us with a conundrum - how does a terrestrial planet transform from temperate to hot-house? For decades it was proposed that the gradual brightening of the sun was the probable cause [5]. Yet 4 billion years ago Venus was receiving nearly 1.4 times the insolation that Earth receives today, and many studies have put Earth at the inner boundary of the habitable zone today [6]. The newer 3-D GCM efforts have demonstrated that if Venus had an early habitable period, that the cloud-albedo feedback responsible for maintaining temperate surface conditions [7] could still be in operation today. From this perspective increasing insolation through time cannot be an answer to the transition from habitable to hot-house. We propose that the 'Great Climate Transition' (GCT) was trigged by simultaneous large igneous provinces (LIPs) akin to those like the Siberian Traps responsible for the End Permian [8]. We have taken the most up to date LIP database for Earth [9] and characterized their distribution through time as random or nearly random. Next we initiate a large suite of Monte Carlo simulations based on this record and generate the likelihood for simultaneous, or environmentally overlapping events in this hypothetical setup. We find the probability of such events to be quite high, a probable cause for Venus' GCT, and a possible harbinger of things to come for Earth.

Venus↗

NASA NTRS1945

Comparison of Pitching Moments Produced by Plain Flaps and by Spoilers and Some Aerodynamic Characteristics of an NACA 23012 Airfoil with Various Types of Aileron

Sectional characteristics of airfoil having retractable slotted flap with plain, slot-lip, or retractable ailerons are presented for a large range of aileron deflections. The analysis indicated that pitching moments produced by spoilers were less positive than those produced by plain flaps of equal effectiveness, also that pitching moments created by the spoiler increased less with the Mach number than similar moments produced by plain flaps. Positive values of pitching moment decreased as devices were located nearer airfoil leading edge.

PITCHING MOMENTS - AIRFOILS↗

DOE OSTI2025

Multiple Twinning in Nacre and Aragonite

Twinning occurs when two crystals share a coherent interface along which their lattices are mirror symmetric. Here, twinning is investigated in biogenic and geologic aragonite (CaCO 3 ) in columnar nacre from the red abalone Haliotis rufescens, sheet nacre from the black-lip pearl oyster Pinctada margaritifera, and geologic aragonite. All samples exhibit the expected single (110) twins, characterized by a 116.2° rotation of the aragonite a-axis. Surprisingly, multiple twins—double, triple, quadruple—are also observed, each involving successive 116.2° rotations of the a-axis around the c-axis. Multiple twinning is concomitant but distinct from the well-known cyclic twinning of aragonite. Multiple twinning is most prevalent in columnar nacre, reaching up to quadruple twins, most frequently occurring between nacre tablets in the same column, whereas sheet nacre and geologic aragonite exhibit up to triple twins. The frequency of twins decreases with increasing twin multiple, consistent with a physical rather than biological origin. This interpretation is supported by observations in geologic aragonite and by simulations of columnar nacre growth, which incorporate only nucleation rate, growth rate, and basic geometric constraints, yet they reproduce the observed twinning behavior in columnar nacre, reinforcing the conclusion that multiple twinning arises from physical growth mechanisms.

Schmidt, Connor A. [Univ. of Wisconsin, Madison, W↗

DOE OSTI2021

New Insights into the High‐Performance Black Phosphorus Anode for Lithium‐Ion Batteries

Abstract Black phosphorus (BP) is a promising anode material in lithium‐ion batteries (LIBs) owing to its high electrical conductivity and capacity. However, the huge volume change of BP during cycling induces rapid capacity fading. In addition, the unclear electrochemical mechanism of BP hinders the development of rational designs and preparation of high‐performance BP‐based anodes. Here, a high‐performance nanostructured BP–graphite–carbon nanotubes composite (BP/G/CNTs) synthesized using ball‐milling method is reported. The BP/G/CNTs anode delivers a high initial capacity of 1375 mA h g −1 at 0.15 A g −1 and maintains 1031.7 mA h g −1 after 450 cycles. Excellent high‐rate performance is demonstrated with a capacity of 508.1 mA h g −1 after 3000 cycles at 2 A g −1 . Moreover, for the first time, direct evidence is provided experimentally to present the electrochemical mechanism of BP anodes with three‐step lithiation and delithiation using ex situ X‐ray diffraction (XRD), ex situ X‐ray absorption spectroscopy (XAS), ex situ X‐ray emission spectroscopy, operando XRD, and operando XAS, which reveal the formation of Li 3 P 7 , LiP, and Li 3 P. Furthermore, the study indicates an open‐circuit relaxation effect of the electrode with ex situ and operando XAS analyses.

Li, Minsi↗

DOE OSTI2025

Revisiting the Impact of Anion Selection on Sulfur Redox Reaction Kinetics for High Sulfur Loading Lithium–Sulfur Batteries

Lithium bis(trifluoromethane)sulfonimide (LiTFSI) is widely used in lithium–sulfur (Li–S) battery electrolytes due to its stability with lithium polysulfides (LiPSs) and moderate compatibility with lithium metal anodes. However, LiTFSI presents environmental concerns due to its association with per- and polyfluoroalkyl substances (PFAS), which are environmentally persistent and potentially toxic, raises sustainability concerns. This research also reveals that LiTFSI limits sulfur redox reactions (SRRs), making it less effective than other lithium salts. Additionally, some salts previously considered incompatible with Li-S systems due to their reactivity with LiPSs are demonstrated to perform effectively. For the first time, a protective, porous cathode electrolyte interphase (CEI) formed in situ through reactions between salt anions and LiPS is reported. The cells delivered a high specific capacity of 1230.8 mAh g −1 at 0.05 C with a sulfur loading of ≈6 mg cm −2 , limited lithium anode, maintaining a capacity retention of 76.2% after 100 cycles at 0.1 C. Under harsh conditions, such as high sulfur loading, lean electrolyte conditions (3 µL mg −1 ), and in anode-free cells, the cells continued to deliver outstanding capacity. This work provides valuable guidelines for understanding and selecting lithium salts to advance electrolyte design for Li–S batteries.

high loading batteries↗

DOE OSTI2020

Associations between cumulative environmental quality and ten selected birth defects in Texas

Abstract Background Causes of most birth defects are largely unknown. Genetics, maternal factors (e.g., age, smoking) and environmental exposures have all been linked to some birth defects, including neural tube, oral cleft, limb reduction, and gastroschisis; however, the contribution of cumulative exposures across several environmental domains in association with these defects is not well understood. Methods The Environmental Quality Index (EQI) and its domains (air, water, land, sociodemographic, built) were used to estimate county‐level cumulative environmental exposures from 2006–2010 and matched to birth defects identified from Texas Birth Defects Registry and live birth records from births in years 2007–2010 ( N = 1,610,709). Poisson regression models estimated prevalence ratios (PR) and 95% confidence intervals (CI) for associations between 10 birth defects and the EQI. Results We observed some positive associations between worst environmental quality and neural tube, anencephaly, spina bifida, oral cleft, cleft palate, cleft lip with and without cleft palate, and gastroschisis [PR range: 1.12–1.55], but near null associations with limb reduction defects. Among domain specific results, we observed the strongest positive associations with the sociodemographic domain across birth defects but varied positive associations among the air and water domains, and negative or null associations with the land and built domains. Overall, few exposure‐response patterns were evident. Conclusions Our results highlight the complexities of cumulative, simultaneous environmental exposures in the prevalence rates of 10 selected birth defects. We were able to explore the impact of overall and domain specific environmental quality on birth defects and identify potential domain specific drivers of these associations.

Krajewski, Alison K.↗

DOE OSTI2020

Mercury linked to Deccan Traps volcanism, climate change and the end-Cretaceous mass extinction

Mercury (Hg) anomalies linked to Large Igneous Provinces (LIP) volcanism have been identified in sediments across all five major mass extinctions in Earth's history. This study tests whether Hg in marine sediments is a reliable proxy linking Deccan Traps volcanic eruptions to late Maastrichtian global climate warming and the mass extinction at the Cretaceous-Paleogene boundary (KPB). Our primary test site is the Elles section in Tunisia, the auxiliary Global Stratotype Section and Point (GSSP) to El Kef. Elles has the most complete marine sedimentary record and a high average sedimentation rate of ~4.7 cm/ky. Here, we chose the Hor Hahar section in Israel to corroborate the geographic distribution of Hg fallout from Deccan volcanism. Reliability of the Hg proxy over the last 550 ky of the Maastrichtian to early Danian was evaluated based on high-resolution age control (orbital cyclostratigraphy), stable isotope climate record, Hg concentrations, biotic turnover and mass extinction. These results were correlated with the pulsed Deccan eruptive history constrained previously by U-Pb zircon geochronology. Our results support Hg as robust proxy for Deccan volcanism with large Hg spikes marking “extreme event” (EE) pulsed eruptions correlative with climate warming peaks separated by steady, less intense eruptions. Long-term global climate warming began near ~350 ky pre-KPB, reached maximum warming (3–4 °C) between 285 and 200 ky pre-KPB, followed by gradual cooling and rapid temperature drop between 45 and 25 ky pre-KPB. During the last 25 ky before the KPB, multiple Hg EE eruptions correlate with hyperthermal warming that culminated in the rapid mass extinction at Elles during ≤1000 years of the Cretaceous. These latest Cretaceous Hg peaks may correlate with massive, distal, Deccan-sourced lava flows (>1000 km long) that traversed the Indian subcontinent and flowed into the Bay of Bengal, bracketing the mass extinction. These results support Deccan volcanism as a primary driver of the end-Cretaceous mass extinction.

54 ENVIRONMENTAL SCIENCES↗