Decoding the mechanophysiology for inhaled onset of smallpox with model-based implications for mpox spread.

In this study, high-Fidelity Large eddy simulation (LES) data was used to create a surrogate turbulence model to enhance the estimation of turbulent heat flux in a Reynolds averaged Navier Stokes (RANS) solver for film cooling applications. The LES simulation (A flat plate film cooling application with a Reynolds number of 17,382, a blowing ratio of 1 and a density ratio of 2) was validated by comparison with experimental data. A correlation analysis was performed to identify the most influential parameters, and temperature gradient, velocity gradient, turbulent dissipation rate, shear strain rate, and turbulent viscosity ratio were selected as the most effective parameters. A second model was developed to create a Galilean-invariant model that remains unaffected by changes in the coordinate system. Neural network was applied to the LES training data to propose a modified surrogate dynamic turbulent Prandtl number to be applied to the k − ε realizable RANS simulation. The first surrogate model was implemented to two different geometries, one geometry was a flat plate film cooling similar to the training data but with different flow conditions, and another one was a more complex geometry with pressure gradient. The second model was only implemented on the second geometry and produced similar results. The surrogate models predicted a more accurate thermal field near the cooling wall (up-to 58 % error reduction) with a computational time complexity similar to the base RANS solver.

In response to the recent COVID-19 pandemic, Ultraviolet (UV) air purifiers have emerged as a recommended mitigation strategy to deactivate airborne viruses and reduce infection spread within enclosed spaces. This paper focuses on developing a high fidelity computational methodology to investigate the efficacy of such devices. Large Eddy Simulations are used to resolve the turbulent flow inside the purifier with 2 UV lamps activated for specified operating conditions. A fully coupled, or two-way coupling approach, is compared with a computationally efficient one-way coupling method. Once the Eulerian flow reaches statistical convergence, time-averaged velocity and temperature distributions are extracted and provided to an Eulerian-Lagrangian framework to examine the turbulent dispersion of virus-laden droplets based on a frozen flow approach. These simulations incorporate an evaporation model for virus-laden droplets, highlighting the importance of accounting for this physical phenomenon. The majority of droplets exiting the purifier are identified as droplet nuclei containing non-volatile matter and virus copies. The survival rate of these expelled virus-laden droplets is determined using a UV radiation disinfection solver, developed and validated based on existing experimental studies. The resulting inactivation rate of the UV air purifier reaches 99%, highlighting its potential as an effective mitigation strategy. • A solver coupling Large Eddy Simulation, Lagrangian dispersion, UV radiation and virus disinfection has been set up. • Simulation of a UV purifier with high-fidelity Large Eddy Simulation has been performed. • Performances of a UV purifier have been investigated for different UV lamp radiation.

This paper demonstrates the development of a simple chemical kinetics model designed for autoignition of n-dodecane in air using Bayesian inference with a model-error representation. The model error, i.e. intrinsic discrepancy from a high-fidelity benchmark model, is represented by allowing additional variability in selected parameters. Subsequently, we quantify predictive uncertainties in the results of autoignition simulations of homogeneous reactors at realistic diesel engine conditions. We demonstrate that these predictive error bars capture model error as well. The uncertainty propagation is performed using non-intrusive spectral projection that can also be used in principle with larger scale computations, such as large eddy simulation. While the present calibration is performed to match a skeletal mechanism, it can be done with equal success using experimental data only (e.g. shock-tube measurements). Since our method captures the error associated with structural model simplifications, we believe that the optimised model could then lead to better qualified predictions of autoignition delay time in high-fidelity large eddy simulations than the existing detailed mechanisms. This methodology provides a way to reduce the cost of reaction kinetics in simulations systematically, while quantifying the accuracy of predictions of important target quantities.

Mitigation of flow-induced pressure fluctuations in a Francis turbine operating at the design and partial load regimes—LES simulations

The axial flow in rod bundles has been the object of several investigations, since they are relevant for various industrial applications (e.g., heat exchangers, nuclear reactor cores). For tight configurations (pitch-to-diameter ratio smaller than 1.1) the large difference in velocity within the cross section creates the possibility of a Kelvin-Helmholtz instability and the generation of a vortex street in the gap (“gap instability”). While the presence of spacing devices may perturb the flow, simple grid spacers — grids of the type usually encountered in sodium fast reactors — do not prevent this instability. This work seeks to improve our understanding of the gap instability in large rod bundles by using high-fidelity large-eddy simulation (LES). The application of LES methods has been historically limited to single-pin calculations because of the large cost of full-bundle calculations. However, using Nek5000, a massively parallel spectral-element computational fluid dynamics code, we are able to carry out well-resolved LES simulations for this class of geometries. Results are compared with experimental data. For the largest bundle case, over 8 billion collocation points at a polynomial order of 20 are judged necessary to achieve overall excellent accuracy. More than 500,000 processors are used to carry out the simulations (costing approximately 50,000,000 CPU-hours), and 3,000 snapshots of the flow field have been collected to apply several coherent structure recognition techniques, including one of the largest proper orthogonal decompositions carried out to date. Also investigated here is the effect of geometry, including the (presence of spacers, changing pitch-to-diameter ratio, and canister wall. In particular, global linear stability analysis is applied to a series of simplified geometries in order to gain insight into the physics of the gap instability.

Toward prediction of turbulent atmospheric flows over propagating oceanic waves via machine-learning augmented large-eddy simulation

High-fidelity large-eddy simulations (LESs) are performed to investigate aeroacoustic characteristics of jets issuing from twin rectangular nozzles with an aspect ratio of 2:1 at two overexpanded conditions and the design condition. For all three jet conditions simulated, LES predicts qualitatively similar near-field flow statistics to those measured at the University of Cincinnati. Using the Ffowcs Williams-Hawkings method, LES captures the fundamental screech tone and its harmonics fairly well at multiple observer locations in the far-field. Intense jet flapping motions in the near field along the minor axis, which are influenced by jet-to-jet interactions, are found to correspond to those frequencies. Moreover, the predicted overall sound pressure levels are within 1–2 dB of the experimental measurements. However, the screech tones appear to be intermittent, as the twin-jet interaction pattern varies irregularly. To extract dominant flow structures at the screech frequencies and identify the twin-jet coupling modes, spectral proper orthogonal decomposition (SPOD) analysis is used. SPOD analysis recovers energetic peaks at the screech frequencies, and the corresponding leading modes indicate strong upstream radiation originating from the fifth/sixth shock cells. For the two overexpanded conditions, the leading modes show antisymmetric coupling in the minor axis at the fundamental screech frequencies. In contrast, the two jets behave symmetrically with respect to each other in the major axis, in line with the absence of jet flapping in this direction. Furthermore, the leading SPOD eigenvalues turn out to be, at least, two orders of magnitude larger than higher-order eigenvalues, suggesting potential of reduced-order models for the twin-jet screech.

Aerodynamic performance improvements for a Savonius turbine above a forward-facing step via inclined solar panel: A computational study

FAST.Farm is a newly developed multiphysics, midfidelity engineering tool that can be used to predict turbine power and structural loads of wind turbines in a wind farm with minimal computational expense. Previous studies have shown similarities and differences in wind turbine performance between FAST.Farm and high-fidelity large-eddy simulations (LES) using both LES precursor-generated inflow and TurbSim-generated synthetic inflow. While conservative resolutions have been used to date, no formal spatial or temporal discretization study has been performed for the FAST.Farm model wind domains. This work aims to study the effects of varying the spatial and temporal discretization of the wind domains on wake meandering (low-resolution domain) and turbine structural response (high-resolution domains) and resulting wake and load calculations. The purpose of this study is to establish convergence criteria and recommendations for discretization values in terms of rotor diameter (D, expressed in meters) that will maximize computational efficiency. To ensure a percent error of ≤ 1% in standard deviation of wake center position relative to the finest included resolution, a low-resolution time step of 0.024D s, 0.016D s, and 0.0079D s and a low-resolution spatial discretization of 0.079D m, 0.16D m, and 0.24D m is recommended for 8 m/s, 12 m/s, and 18 m/s mean ambient wind speed at hub height, respectively. These guidelines are likely applicable to other implementations of the dynamic wake meandering model. To ensure a percent error of ≤ 1% in standard deviation of all considered structural response outputs, a high-resolution time step that captures the highest influential excitation and natural frequencies in the system and a high-resolution spatial discretization comparable to the maximum airfoil cord length is recommended. These guidelines are likely applicable to any aeroelastic analysis.

A flow control strategy for the delay of unsteady separation and dynamic stall on a pitching NACA 0012 airfoil is explored by means of high-fidelity large-eddy simulations. The flow fields are computed employing a high-fidelity large-eddy simulation (LES) approach. The flow parameters are freestream Mach number M∞ = 0.1 and chord Reynolds numbers Rec = 5× 10. Both constant-rate and oscillatory pitching motions are considered. For the baseline cases, dynamic stall is initiated with the bursting of a contracted laminar separation bubble (LSB) present in the leading-edge region. This observation motivated a flow control approach employing high-frequency pulsed actuation imparted through a zero-net mass flow blowing/suction slot located on the airfoil lower surface just downstream of the leading edge. For the constant-rate pitching case, both pulsed and harmonic spanwise-nonuniform forcing are considered with a maximum non-dimensional frequency Stf = fc/U = 50.0 which corresponds to a sub-harmonic of the dominant natural LSB fluctuations for a baseline static case used for reference purposes. A significant delay in the onset of dynamic stall is demonstrated with pulsed forcing at high frequencies (Stf = 25.0, 50.0), however, control effectiveness diminishes with decreasing frequency. At Stf = 12.5, pulsed actuation is shown to be superior to harmonic forcing suggesting that the higher harmonic content present in the pulsed mode is still capable of energizing the LSB. For the oscillatory pitching motion, pulsed high-frequency flow control with Stf = 50.0) is considered for two cases exhibiting light and deep dynamic stall respectively. For light dynamic stall, flow actuation is capable of maintaining an effectively attached flow during the entire pitching cycle thereby inhibiting the formation of large-scale leading-edge and shear-layer vortical structures. For deep dynamic stall, control is found to also be very effective in eliminating leading-edge separation and the formation of a dynamic stall vortex. Nonetheless, trailing-edge separation eventually occurs at high incidence. For both cases, actuation provided a significant reduction in the cycle-averaged drag and in the force and moment fluctuations. In addition, the negative (unstable) net-cycle pitch damping found in the baseline cases was eliminated.

To predict harmful acoustic loading observed at lift-off of the launch vehicle, aero-vibro acoustic simulation technique is developed. High-fidelity large-eddy simulation with computational aeroacoustics based on the full Euler equations in time domain are employed to predict generation of the acoustic waves and their propagation to the fairing. Coupled vibro-acoustic analysis based on finite element method are applied to compute the transmitted acoustic wave into the fairing both in the time and frequency domains. Acoustic measurement of a simplified fairing model with a subscale liquid rocket engine is conducted, and validation study of the present technique is performed. Reasonable agreement is obtained for peaks of the acoustic spectrum taken inside the fairing model. Such peaks are found to be related to the internal acoustic modes and ring modes of the faring structure. However, further study is required to obtain quantitative agreement.

A high-fidelity large-eddy simulation and unsteady flamelet combustion model construct is deployed to numerically investigate the effects of crosswind magnitude and pool fire shape on large-scale pool fire attributes. These include general flame dynamics, flame shape and radiative flux magnitude in and around the fire. Three pool fire shapes at a nominal length scale of 10 m are subjected to four crosswind magnitudes between 0 and 20 m s $^{-1}$ . The pool shapes studied are circular, square and rectangular. The study includes the sensitivity of parameters to mesh and time step refinement. Results demonstrate that the rectangular shape, under crosswind, has low-levels of vertical velocity induction, resulting in a plume that is closer to the ground. In the quiescent regime, under-resolved meshes provide a higher radiative heat flux prediction compared with the most refined mesh. However, as crosswind increases, low mesh resolutions underpredicted radiative flux. This is due to the coarse mesh resolution not capturing small-scale vortical features that increased mixing and combustion efficiency. A transition of peak radiative flux with respect to crosswind occurs from the leeward- to windward-side of the pool, while sharp pool features result in larger radiative heat fluxes concentrated in regions of high scalar dissipation rate.

The design of fuel injection schemes is crucial for improving the combustion performance of high-Mach number scramjet. To clarify the feasibility of the coaxial jet injection scheme, high fidelity Large Eddy Simulation of the supersonic coaxial jet flame is conducted. The simulations are in good agreement with the experimental results in terms of time-averaged velocity, temperature, and species distribution. Auto-ignition phenomenon and the characteristics of partially premixed flame are well captured. The introduction of co-flow air increases the vorticity magnitude close to the injection port and downstream near-wall region, which results in a 400 K rise in the time-averaged temperature on the downstream near-wall region and a 4% increase in the proportion of premixed combustion near the injection port. Moreover, the instantaneous distribution of hydroxy radical indicates that the spanwise width of the windward reaction shear layer is reduced utilizing the coaxial jet scheme. Chemical kinetic analysis is applied to reveal the propagation mechanism of partially premixed flames. Thermal explosion is the chemical explosion mode for all coaxial jet flame front, which are dominated by a high-temperature reaction path. The low-temperature reaction path mainly exists in the transverse jet injection port, downstream near-wall region of the single transverse jet and co-flow lifted flame base. These significant findings provide valuable insights for the potential engineering application of the coaxial jet injection scheme to a high Mach number scramjet.

Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback.The EU H2020 ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3.The micromix combustor comprises thousands of small diffusion flames where air and fuel are mixed in a crossflow pattern.This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity.The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and lowtemperature small diffusion flames in lean overall equivalence ratios.In order to mature the hydrogen micromix combustion technology, high quality numerical simulations of the resulting short, thin and highly dynamic hydrogen flames, as well as predictions of combustion species, are essential.In fact, one of the biggest challenges for current CFD has been to accurately model this combustion phenomenon.The Flamelet Generated Manifold (FGM) model is a combustion model that has been used in the past decades for its predicting capabilities and its low computational cost due to its reliance on pre-tabulated combustion chemistry, instead of directly integrating detailed chemistry mechanisms.However, this trade for a lower computational cost may have an impact on the solution, especially when considering a fuel such as Hydrogen.Therefore, it is necessary to compare the FGM model to another combustion modelling approach which uses more detailed complex chemistry.The main focus of this paper then, is to compare the flame characteristics in terms of position, thickness, length, temperature and emissions obtained from LES simulations done with the FGM model, to the results obtained with more complex chemistry models, for hydrogen micromix flames.This will be done using STAR-CCM+ to determine the most suitable numerical approach required for the design of injection systems for ultra-low NOx.

Critical exposure duration for the test targets in measurement of visual function is sometimes very important, because even though patients demonstrate relatively high levels of visual acuity using conventional methods, they may for example occasionally require longer stimulus duration for proper reading of the acuity targets. In our previous study1) we reported that the critical duration of Landolt 'C' visual acuity was significantly prolonged in eyes with central serous retinochoroidopathy and macular edema. But the critical duration for the increment threshold was not prolonged in these diseased eyes, although the mean relative threshold energy of the diseased groups was significantly higher than that of the control group. We then measured the critical duration of achromatic2) and chromatic) grating visual acuity in a normal eye, with the purpose of clarifying the mechanisms behind these phenomenon. The critical duration of achromatic grating visual acuity in the normal subject was 73.0 and 140 msec under two different brightness conditions (Fig. 1), and these were significantly shorter than the results of the Landolt ‘C’ visual acuity test (0.62 sec., n=17 as shown in Fig. 2). The critical duration of red-green grating acuity under the 4 different conditions in the same subject was 129, 134, 136 and 129 msec (ARVO 1997, Fig. 3). These were similar to one result in the achromatic grating study (140 ms, white background=23.2 cd/sqm, contrast=73.1%).