Choked Flow in a Converging/Diverging Rotating Detonation Engine Exit
Presentation presenting results of the NETL water-cooled RDE.
Weber, Justin↗
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Reinforcing the exit hole from friction stir welding and processing
After friction stir welding/processing (FSW/P), an exit hole remains at the end of the run, which can be the weakest region of the welded/processed workpiece. In addition, tensile residual stress around the exit hole resulting from heating during FSW/P facilitates incipient crack initiating from the exit hole under external loading. Current solutions include removing or repairing the exit hole, which are time-consuming and costly. Here, we propose a novel method to reinforce the exit hole by applying an additional FSW/P pass around it, in a way that replaces preexisting tensile residual stress with compressive residual stress. Under external loading, there is no evident strain accumulation around the exit hole, and the workpiece ultimately fails along the FSW/P heat affected zone. This method provides a more convenient way to reinforce the exit hole than the current exit-hole repair or removal methods for industrial applications.
36 MATERIALS SCIENCE↗
Reconstructing the exit wave of 2D materials in high-resolution transmission electron microscopy using machine learning
Reconstruction of the exit wave function is an important route to interpreting high-resolution transmission electron microscopy (HRTEM) images. Here we demonstrate that convolutional neural networks can be used to reconstruct the exit wave from a short focal series of HRTEM images, with a fidelity comparable to conventional exit wave reconstruction. We use a fully convolutional neural network based on the U-Net architecture, and demonstrate that we can train it on simulated exit waves and simulated HRTEM images of graphene-supported molybdenum disulphide (an industrial desulfurization catalyst). We then apply the trained network to analyse experimentally obtained images from similar samples, and obtain exit waves that clearly show the atomically resolved structure of both the MoS 2 nanoparticles and the graphene support. We also show that it is possible to successfully train the neural networks to reconstruct exit waves for 3400 different two-dimensional materials taken from the Computational 2D Materials Database of known and proposed two-dimensional materials.
2D materials↗
Long-term patterns of cave-exiting activity of hibernating bats in western North America
Understanding frequency and variation of cave-exiting activity after arousal from torpor of hibernating bats is important for bat ecology and conservation, especially considering white-nose syndrome. In winter from 2011 to 2018, we acoustically monitored, and counted in hibernacula, two species of conservation concern—western small-footed myotis ( Myotis ciliolabrum ) and Townsend’s big-eared bats ( Corynorhinus townsendii )—in 9 caves located in important habitat for these species in western North America. We investigated if cave-exiting activity differed by species, cave, number of hibernating bats, moon phase, and weather variables. Both species exited hibernacula during all winter months, but most activity occurred in March followed by November. Although we counted almost 15 times more Townsend’s big-eared bats during hibernacula surveys, we documented western small-footed myotis exiting caves 3 times more than Townsend’s big-eared bats. Cave-exiting activity increased with increasing number of hibernating bats, but more so for western small-footed myotis. Both species of bats were active during warm weather and low wind speeds. Western small-footed myotis were more active during colder temperatures, higher wind speeds, and greater change in barometric pressure than Townsend’s big-eared bats. Our results provide a long-term dataset of cave-exiting activity after arousal from torpor during hibernation for these species before the arrival of white-nose syndrome.
54 ENVIRONMENTAL SCIENCES↗
Recipes for a Successful Exit for Clean- and Hard-tech Startups
This study demonstrates the combinations of multiple causal factors that formulate a startup’s strategy to successfully “exit”, namely “recipes for a successful exit,” in the clean- and hard-tech sector. We identify seven key causal factors (i.e., causal conditions) that impact startup success, including commercial readiness, investor interactions, favorable industry, non-financial support, straightforward development path, experienced team, and visibility to investors. We also investigate the combinations of selective causal conditions that can provide further synergetic impact. We conduct the fuzzy-set qualitative comparative analysis (fsQCA) on seven US clean and hard-tech startups that exited between 2005 and 2016. The successful companies all demonstrate distinctive characteristics based on three general categories (1) robust ecosystem; (2) heavy-lifting team; or (3) external opportunity. Across these three categories, commercial readiness and strong investor interactions are necessary conditions for all exit cases. But there are important differences that drive success in each category, such as the interaction with non-financial support (in the robust ecosystem case), experienced team (in the heavy-lifting team case), and favorable industry (in the external opportunity case). Furthermore, our findings are meant to support entrepreneurs in reaching an exit by optimizing the given internal and external circumstances, and policymakers to build a robust ecosystem that can increase the success rate of the clean- and hardtech development.
99 GENERAL AND MISCELLANEOUS↗
Increased spatial coherence length from an asymmetric crystal reflection at grazing exit
Coherent X-ray imaging is an active field at synchrotron sources. The images rely on the available coherent flux over a limited field of view. At many synchrotron beamlines a double-crystal monochromator (DCM) is employed in a standard nondispersive arrangement. For coherent diffraction imaging it is advantageous to increase the available field of view by increasing the spatial coherence length (SCL) of a beam exiting such a DCM. Here, Talbot interferometry data together with ray-tracing simulations for a (+ − − +) four-reflection experimental arrangement are presented, wherein the first two reflections are in the DCM and the final fourth reflection is asymmetric at grazing exit. Analyses of the interferometry data combined with the simulations show that compared with the beam exiting the DCM a gain of 76% in the SCL was achieved, albeit with a factor of 20 reduction in flux density, which may not be a severe penalty at a synchrotron beamline. Previous efforts reported in the literature to increase the SCL that employed asymmetric crystal diffraction at grazing incidence are also discussed. A much reduced SCL is found presently in simulations wherein the same asymmetric crystal is set for grazing incidence instead of grazing exit. In addition, the present study is compared and contrasted with two other means of increasing the SCL. These are (i) focusing the beam onto an aperture to act as a secondary source, and (ii) allowing the beam to propagate in vacuum an additional distance along the beamline.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Printability and Overall Cooling Performance of Additively Manufactured Holes With Inlet and Exit Rounding
Abstract To improve cooling effectiveness of gas turbine hardware, various film cooling hole shapes have previously been researched. Unique design modifications have recently been made possible through the design freedom allotted by additive manufacturing (AM). As one example, creating a rounded inlet for a film-cooling hole can mitigate separation at the inlet. This study explores various geometric features by exploiting the uses of additive manufacturing for shaped film cooling holes at engine scale. Both printability and cooling performance were evaluated. Resulting from this study, additively manufactured holes with hole inlet and exit rounding were printed with some variations from the design intent (DI). The largest deviations from the design intent occurred from dross roughness features located on the leeward side of the hole inlet. The measured overall effectiveness indicated that an as-built inlet fillet decreased in-hole convection as well as decreased jet mixing compared to the as-built sharp inlet. Including an exit fillet, which prevented an overbuilt diffuser exit, was also found to decrease jet mixing. A particular insight gained from this study is the importance of the convective cooling within the hole to the overall cooling performance. In-hole roughness, which is a result of additive manufacturing, increased convective cooling within the holes but also increased jet mixing as the coolant exited the hole. The increased jet mixing caused low overall effectiveness downstream of injection.
Engineering↗
Plume-exit modeling to determine cloud condensation nuclei activity of aerosols from residential biofuel combustion
Abstract. Residential biofuel combustion is an important source of aerosols and gases in the atmosphere. The change in cloud characteristics due to biofuel burning aerosols is uncertain, in part, due to the uncertainty in the added number of cloud condensation nuclei (CCN) from biofuel burning. We provide estimates of the CCN activity of biofuel burning aerosols by explicitly modeling plume dynamics (coagulation, condensation, chemical reactions, and dilution) in a young biofuel burning plume from emission until plume exit, defined here as the condition when the plume reaches ambient temperature and specific humidity through entrainment. We found that aerosol-scale dynamics affect CCN activity only during the first few seconds of evolution, after which the CCN efficiency reaches a constant value. Homogenizing factors in a plume are co-emission of semi-volatile organic compounds (SVOCs) or emission at small particle sizes; SVOC co-emission can be the main factor determining plume-exit CCN for hydrophobic or small particles. Coagulation limits emission of CCN to about 1016 per kilogram of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low supersaturation (ssat). Hygroscopic Aitken-mode particles can contribute to CCN through self-coagulation but have a small effect on the CCN activity of accumulation-mode particles, regardless of composition differences. Simple models (monodisperse coagulation and average hygroscopicity) can be used to estimate plume-exit CCN within about 20 % if particles are unimodal and have homogeneous composition, or when particles are emitted in the Aitken mode even if they are not homogeneous. On the other hand, if externally mixed particles are emitted in the accumulation mode without SVOCs, an average hygroscopicity overestimates emitted CCN by up to a factor of 2. This work has identified conditions under which particle populations become more homogeneous during plume processes. This homogenizing effect requires the components to be truly co-emitted, rather than sequentially emitted.
54 ENVIRONMENTAL SCIENCES↗
Internal cooling system with converging-diverging exit slots in trailing edge cooling channel for an airfoil in a turbine engine
An airfoil (10) is disclosed for a gas turbine engine in which the airfoil (10) includes an internal cooling system (14) with one or more converging-diverging exit slots (20) configured to increase the effectiveness of the cooling system (14) at the trailing edge (34) of the airfoil (10) by increasing the contact of cooling fluids with internal surfaces (24, 30) of the pressure and suction sides (36, 38) of the airfoil (10). In at least one embodiment, the trailing edge cooling channel (18) may include one or more converging-diverging exit slots (20) to further pressurize the trailing edge cooling channel (18) and may be formed by a first and second ribs (80, 82) extending between an outer walls (13, 12) forming the pressure and suction sides (36, 38). The converging-diverging exit slot (20) may be formed from a first converging section (84) having an inlet (86) with a larger cross-sectional area than an outlet (88) and is formed from a second diverging section (90) having an inlet (92) with a smaller cross-sectional area than an outlet (94).
42 ENGINEERING↗
Effect of a Diffuser on Conditioning Flow Field Fluctuations at the Exit of a Rotating Detonation Combustor
Pressure gain combustion (PGC) seeks to convert fuel’s chemical energy simultaneously into thermal energy and mechanical energy, thereby reducing the entropy production in the process. Recent research has shown that the rotating detonation combustion or combustor (RDC) can provide excellent specific thrust, specific impulse, and large pressure gain through rapid energy release by continuous detonation in the circumferential direction. In this study, we present experimental results from RDC operated on methane and oxygen-enriched air to represent reactants used in gas turbines for land-based power generation. A thorough understanding of the velocity flow field exiting the combustor is important to develop future rotating detonation engine (RDE) designs, as well as to successfully implement the flow conditioning devices to power generating turbine hardware located downstream. The RDC is operated at high pressures in two ways through this study: 1) placing a back-pressure plate (BPP) downstream of the annular combustor, and 2) placing a diffuser downstream of the annular combustor. Time-resolved particle image velocimetry (TR-PIV) is applied at a frame rate of 50 kHz to quantify the RDC exit flow. A qualitative analysis is presented with vector data obtain from experimental testing. Results show that for the BPP configuration the highly periodic exit flow tilts in the azimuthal direction, indicating a significant circumferential velocity component. For the diffuser configuration the flow is dominantly axial, with an insignificant circumferential velocity component. The flow field undergoes cyclic fluctuations with the BPP, but not so with the diffuser. Results also show the challenges associated with achieving uniform seed distribution in this highly transient and rapidly changing flow field.
03 NATURAL GAS↗
Exit Flow Field of Methane-Fueld Rotating Detonation Engine Measured by Time Resolved Particle Image Velocimetry
Pressure gain combustion (PGC) seeks to convert fuel’s chemical energy simultaneously into thermal energy and mechanical energy, thereby reducing the entropy production in the process. Recent research has shown that the rotating detonation combustion or combustor (RDC) can provide excellent specific thrust, specific impulse, and large pressure gain through rapid energy release by continuous detonation in the circumferential direction. However, few past studies have employed fuels relevant to power generation gas turbines, since RDC research has focused mainly on aerospace applications. In this study, we present experimental results from RDC operated on methane and oxygen-enriched air to represent reactants used in gas turbines for land-based power generation. The RDC is operated at high pressures by placing a back-pressure plate downstream of the annular combustor. We apply time-resolved particle image velocimetry (PIV) technique, for the first time, to quantify the RDC exit flow at framing rate of 30 kHz. Results show that even though the exit flow is dominantly axial, a significant circumferential velocity component is also present, highlighting the need to condition the flow between RDE exit and turbine inlet. The flow field undergoes cyclic fluctuations, and the key features of the flow field repeat during each cycle. Interestingly, the circumferential velocity shows a reversal in the direction during the cyclic process. Results also show noticeable cycle-to-cycle variations, related to changes in the detonation wave speed, ultimately caused by the rapid fuel-air mixing process at the RDC inlet prior to detonation.
03 NATURAL GAS↗
A Feynman-Kac based numerical method for the exit time probability of a class of transport problems
The exit time probability, which gives the likelihood that an initial condition leaves a prescribed region of the phase space of a dynamical system at, or before, a given time, is arguably one of the most natural and important transport problems. In this work, we present an accurate and efficient numerical method for computing this probability for systems described by non-autonomous (time-dependent) stochastic differential equations (SDEs) or their equivalent Fokker-Planck partial differential equations. The method is based on the direct approximation of the Feynman-Kac formula that establishes a link between the adjoint Fokker-Planck equation and the forward SDE. The Feynman-Kac formula is approximated using the Gauss-Hermite quadrature rules and piecewise cubic Hermite interpolating polynomials, and a GPU accelerated matrix representation is used to compute the entire time evolution of the exit time probability using a single pass of the algorithm. The method is unconditionally stable, exhibits second order convergence in space, first order convergence in time, and it is straightforward to parallelize. Applications are presented to the advection diffusion of a passive tracer in a fluid flow exhibiting chaotic advection, and to the runaway acceleration of electrons in a plasma in the presence of an electric field, collisions, and radiation damping. Benchmarks against analytical solutions as well as comparisons with explicit and implicit finite difference standard methods for the adjoint Fokker-Planck equation are presented.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Highly resolved Eulerian simulations of fuel spray transients in single and multi-hole injectors: Nozzle flow and near-exit dynamics
In high pressure fuel injectors, needle opening and closing transients cause complex off-design fluid dynamics behaviors that profoundly impact the spray and mixture formation processes. These dynamics are completely different from what is known to occur in steady state conditions. In this study, diesel spray transients have been investigated in single-hole and 3-hole nozzles, encompassing internal and external nozzle flow and including needle motion, performing highly resolved (2.5 μm) computational fluid dynamics (CFD) simulations. We focused on end-of-injection (EOI) and start-of-injection (SOI) processes, in order to provide insights in to the physics. The liquid fuel, vapor and gas species are modeled with a single-fluid multiphase mixture approach, with diffuse interface, and with large eddy simulations (LES) of the turbulence. Occurrence of phase change due to cavitation is accounted for, and the spray dispersion is described with a turbulent dispersion model. Detailed needle motion data and orifice internal surface are available from xray synchrotron source measurements carried out at Argonne National Laboratory, and shared through the Engine Combustion Network (ECN) community. Simulations are compared against x-ray phase contrast imaging and radiography of the internal and near-exit flow, in addition to optical microscopy data of the near-exit sprays. Simulation results are found to agree well with available experimental data, and are able to realistically capture local and global features. The simulations allow to gain insight into the physics of gas ingestion and dribbles at EOI, for different hole diameters, operating conditions and number of holes. At SOI, timing of liquid appearance out of the injector and spray tip penetration are adequately predicted, by using the EOI flow field as in-nozzle initialization, and by prescribing the measured tip needle displacement with an informed effective valve opening point inferred from the x-ray observations. Lastly, the variation of spreading angle over time is also discussed in detail for the multi-hole case, including hole-to-hole variations. Due to real geometry features and asymmetric needle motion with eccentric components, it is found that the three holes exhibit swirling flows of increasing intensity as the lift decreases, causing the near cone angle to open and spread, in a quasi-hollow cone structure. These features are not observed in axial single-hole injectors because of their relative simplicity and intrinsic symmetry.
42 ENGINEERING↗
Investigation of CrMnV and CrMnTiV multi principal element alloys thin films for use as exit windows of electron beam accelerators
Here, this study explores CrMnV and CrMnTiV multi principal element alloy (MPEA) films as candidates for electron beam exit windows in industrial, high-power accelerators. Films were deposited via magnetron sputtering on various substrates and exposed to 66 kGy of 10 MeV e-beam irradiation. Structural and mechanical properties were analyzed using FESEM, XRD, and nanoindentation. CrMnTiV films exhibited superior grain uniformity and hardness, regardless of the substrate type. Compared to bulk materials, both MPEA films demonstrated higher hardness and excellent radiation resistance. These results highlight the potential of MPEA films as durable, radiation-tolerant materials for high-performance accelerator exit window applications.
Electron Beam Irradiation↗
Swift and extensive Omicron outbreak in China after sudden exit from ‘zero-COVID’ policy
In late 2022, China transitioned from a strict ‘zero-COVID’ policy to rapidly abandoning nearly all interventions and data reporting. This raised great concern about the presumably-rapid but unreported spread of the SARS-CoV-2 Omicron variant in a very large population of very low pre-existing immunity. By modeling a combination of case count and survey data, we show that Omicron spread extremely rapidly, at a rate of 0.42/day (95% credibility interval: [0.35, 0.51]/day), translating to an epidemic doubling time of 1.6 days ([1.6, 2.0] days) after the full exit from zero-COVID on Dec. 7, 2022. Consequently, we estimate that the vast majority of the population (97% [95%, 99%], sensitivity analysis lower limit of 90%) was infected during December, with the nation-wide epidemic peaking on Dec. 23. Overall, our results highlight the extremely high transmissibility of the variant and the importance of proper design of intervention exit strategies to avoid large infection waves.
60 APPLIED LIFE SCIENCES↗
Differences in the path to exit the ribosome across the three domains of life
The ribosome exit tunnel is an important structure involved in the regulation of translation and other essential functions such as protein folding. By comparing 20 recently obtained cryo-EM and X-ray crystallography structures of the ribosome from all three domains of life, we here characterize the key similarities and differences of the tunnel across species. We first show that a hierarchical clustering of tunnel shapes closely reflects the species phylogeny. Then, by analyzing the ribosomal RNAs and proteins, we explain the observed geometric variations and show direct association between the conservations of the geometry, structure and sequence. We find that the tunnel is more conserved in the upper part close to the polypeptide transferase center, while in the lower part, it is substantially narrower in eukaryotes than in bacteria. Furthermore, we provide evidence for the existence of a second constriction site in eukaryotic exit tunnels. Overall, these results have several evolutionary and functional implications, which explain certain differences between eukaryotes and prokaryotes in their translation mechanisms. In particular, they suggest that major co-translational functions of bacterial tunnels were externalized in eukaryotes, while reducing the tunnel size provided some other advantages, such as facilitating the nascent chain elongation and enabling antibiotic resistance.
Biochemistry & Molecular Biology↗
Performance Characteristics of a Rotating Detonation Combustor Exiting Into a Pressurized Plenum to Simulate Gas Turbine Inlet
Abstract The present study aims to experimentally characterize the performance of a rotating detonation combustion (RDC) system integrated with a pressurized downstream plenum to simulate the high-pressure inlet conditions of power-generating gas turbines. A thorough understanding of the operational behavior including wave mode behavior, static pressure profile along the combustor length, and dynamic features of pressure fluctuations is crucial for successful integration of RDC with the turbine. In this study, two RDC configurations are investigated, RDC with a constant area annulus and RDC with a converging nozzle. In both cases, the RDC flow exited into a plenum chamber kept at pressures varying from 155 kPa to 330 kPa. RDC was operated on methane and oxygen-enriched air to represent reactants used in land-based power generation. Experiments were conducted for the two RDCs configurations operated at three reactant mass flow rates (0.23, 0.32, and 0.46 kg/s). The RDC performance is characterized by time-averaged static pressure measurements, and wave velocity determined by ionization probes. In addition, dynamic pressure measurements were recorded both inside and near the exit of RDC channel to investigate wave interactions between RDC and downstream plenum. Results show that the RDC with the converging nozzle achieved superior performance while minimizing detrimental interactions with the reflected shock and/or acoustic waves from the downstream plenum.
Engineering↗
Time-Resolved PIV Measurements of Flow Field at the Exit of a Diffuser Mounted on a Rotating Detonation Combustor
Time-resolved particle image velocimetry at 30 kHz is applied to the exhaust flow field of a RDC system configured with a diffuser geometry and a converging-diverging (CD) nozzle. The RDC is operated with methane fuel and oxygen-enriched air, motivated by power generation applications. The measured flow-field is discretized into axial and non-axial velocity components. Results are shown to characterize the flow-field across a cord length at the exit plane. Instantaneous contours of the two velocity components, and 1D histograms of velocity components, and 2D histograms of total velocity and tilt angle are shown at multiple locations in the flow. Repeatability of the data is evaluated by comparing tests conducted at similar flow rates. Results are presented for a baseline test case, and test cases showing the effect of reactant higher flow rate and CD nozzle geometry. Finally, the results are compared to a previous RDC study without the diffuser to compare the effectiveness of the diffuser and CD nozzle designs in mitigating the flow periodicity at the combustor exit.
particle image velocimetry, pressure gain combusti↗