Air Density Research Articles

Experimental and Numerical Study of Air Flow Reversal Induced by Fire in an Inclined Mine Working

Effective fire prevention in mine workings and tunnels requires a thorough theoretical analysis of the heat and mass transfer processes within these structures. This involves using established models to calculate non-isothermal air flow dynamics in long tunnels and mine workings. While the ventilation of tunnels has been extensively studied, significant challenges persist regarding mine ventilation systems, particularly due to their complex and branched topology. This study aimed to address these challenges and gaps in mine ventilation. We designed a laboratory bench to simulate an inclined mine working with a heat source (fire) and validated a mathematical model of heat and mass transfer in such settings. Using experimental measurements, we verified the model’s accuracy. It is important to note that our experimental and theoretical analyses focused solely on the thermal effects of a fire, without considering the release of harmful impurities. Using the validated model, we conducted multiparameter simulations to identify the conditions leading to the formation of a thermal slug in an inclined mine working and the subsequent reversal of air flow. The simulation data enabled us to determine the dependency of the critical heat release rate on the aerodynamic parameters of the mine working. Additionally, we evaluated the changes in average air density within a mine working at the critical heat release rate. These findings are crucial for the further development of a network-based method to analyze air flow stability in mine ventilation networks during fires.

Turkey vultures tune their airspeed to changing air density.

Animals must tune their physical performance to changing environmental conditions, and the breadth of environmental tolerance may contribute to delineating the geographic range of a species. A common environmental challenge that flying animals face is the reduction of air density at high elevation and the reduction in the effectiveness of lift production that accompanies it. As a species, turkey vultures (Cathartes aura) inhabit a >3000 m elevation range, and fly considerably higher, necessitating that they accommodate for a 27% change in air density (0.890 to 1.227 kg m-3) through behavior, physiology or biomechanics. We predicted that birds flying at high elevation would maintain aerodynamic lift performance behaviorally via higher flight speeds, rather than increases in power output or local phenotypic adaptation. We used three-dimensional videography to track turkey vultures flying at three elevations, and data supported the hypothesized negative relationship between median airspeed and air density. Additionally, neither the ratio of horizontal speed to sinking speed nor flapping behavior varied with air density.

On the application of buoyancy correction in the cup test measurement

The water vapour permeability of building materials is often measured using the cup method. One of usual corrections applied to the measured data is correction for the ambient air buoyant force acting on the cup assembly during weighing, the so-called ‘buoyancy correction’. Although the mathematical formula for the correction is well known, there are two distinct ways for its application to the cup test, which depend on the air permeability and flexibility of the tested sample. The magnitude of the correction can be twice different for the two approaches. This study, at first theoretically describes the use of buoyancy correction for cups with different samples. Then, presents results of the measurement of the air pressure inside cups with different samples which support the theoretical assumptions. Finally, based on numerical simulation, were established limits of use of the calculated buoyancy correction. Many samples of building materials are enough air permeable (air permeance higher than 1 × 10−10 kg/(m2sPa)) or flexible to maintain the air pressure and density in the cup close to ambient conditions. Cups with these samples can be corrected by applying the buoyancy correction to the volume of the air-impermeable parts of the cup assembly. If the air permeance of the sample is lower, the possible residual error after the application of correction can be ±3–7 mg/dm2 of the cup mouth area. The application of buoyancy correction can reduce the measurement time, especially for samples with a higher vapour resistance.

Atmospheric density estimation in very low Earth orbit based on nanosatellite measurement data using machine learning

The atmospheric density in the very low Earth orbit (VLEO), the lower region of the thermosphere is a critical factor for satellite missions on prediction of orbit and lifetime. However, accurately determining atmospheric density remains challenging owing to difficulties in acquiring data within the VLEO. The re-Entry satellite with Gossamer aeroshell and GPS/Iridium (EGG) nanosatellite mission, conducted in 2017, obtained sparse coordinate data through the iridium network and Global Navigation Satellite System (GNSS). Using these data, we developed a methodology based on machine learning and special perturbations to estimate atmospheric density. The originally obtained atmospheric density predicted by NRLMSISE-00 was corrected during trajectory reproduction from GNSS data by special perturbation. The prediction performance of the method was validated using the generated trajectory data. Subsequently, we estimated the density at altitudes of approximately 200 km, particularly in the lower region of the VLEO. Density values that accurately reproduced trajectories of the EGG were 0.5 to 0.64 times greater than that predicted by the NRLMSISE-00 model. This methodology is effective for measuring atmospheric density in the lower VLEO region using GNSS data from low-cost and high-frequency nanosatellite missions. By increasing the availability of accurate atmospheric density data, this methodology enhances our understanding of the atmosphere in the VLEO.

Polyenergetic reconstruction mitigates streak artifacts by dual source imaging in chest photon counting detector computed tomography

ObjectiveThis study aims to assess the efficacy of polyenergetic reconstruction methods in reducing streak artifacts caused by dual source imaging in Photon Counting Detector Computed Tomography (PCD-CT) imaging, thereby improving image quality and diagnostic accuracy. MethodsA retrospective cohort study was conducted, involving 50 patients who underwent chest Computed Tomography Angiography with PCD-CT, focusing on those with streak artifacts. Quantitative and qualitative analyses were performed on images reconstructed using monoenergetic and polyenergetic techniques. Quantitative evaluations measured the attenuation of tracheal air density in regions affected by streak artifacts, while qualitative assessments employed a modified Likert scale to rate image quality. Statistical analyses included Wilcoxon's signed-rank tests and Spearman's correlation, alongside assessments of inter-rater reliability. ResultsThere was significantly lower attenuation of tracheal air density on the polyenergetic reconstructions (Median − 1010 ± 62 HU vs −930 ± 110 HU; P < 0.001), and significantly decreased variation on the polyenergetic reconstructions (Median 65.2 ± 79.5 HU vs 38.8 ± 33.9 HU; P < 0.001). The median modified-Likert scale were significantly better for the polyenergetic reconstructions (median modified-Likert 4 ± 0.5 vs 2.5 ± 1; P < 0.001). The inter-rater agreement was substantial and not significantly different between reconstructions (Gwet's ACPolyenergetic = 0.78 vs Gwet's ACVMI = 0.775). ConclusionPolyenergetic reconstruction significantly mitigates streak artifacts in PCD-CT imaging, enhancing quantitative and qualitative image quality. This advancement addresses a known limitation of current PCD-CT reconstruction techniques, offering a promising approach to improving diagnostic reliability and accuracy in clinical practice. We demonstrate that future software implementations can resolve this artifact.

3- and 6-degree-of-freedom analysis of the Magellan aerobraking experiment and planar aerobraking at Venus

The first non-Earth aerobraking experiment occurred in 1993 as part of the Magellan satellite's mission to Venus. Magellan reduced its orbit from elliptical to nearly circular over a span of 70 Earth days by leveraging the non-conservative force of aerodynamic drag to reduce its orbital energy via transiting the upper region of Venus' sensible atmosphere. First tested with the Hiten probe in the Earth-Moon system in 1991, the subsequent Magellan experiment helped prove the viability of aerobraking for planetary missions and paved the way for its implementation in Mars missions starting in the late 1990s and the 2014 Venus Express mission. This paper, for the first time in literature, investigates the Magellan aerobraking experiment from the perspective of both 3- and 6-degree-of-freedom analysis. Multiple atmospheric density models are considered, as well as J4 gravitational perturbations in order to understand the complexity and sensitivity of numerous aerobraking maneuvers in the thick Venusian atmosphere. Alternative satellites are also studied to ascertain their capability of maintaining the Magellan aerobraking flight profile. So as to examine a wide range of vehicle mass and drag reference area, the Hubble Space Telescope (HST) and Hiten satellites are modeled and their aerobraking performance analyzed for the hypothetical case of Venus orbital operations. When reconstructing the historical Magellan aerobraking maneuvers, 3DOF and 6DOF analysis yielded minimal trajectory deviation with the Magellan and Hiten models, while more significant deviation was experienced with the larger HST model. Both 3DOF and 6DOF analyses also reveal the sensitivity of the atmospheric density model and indicate a higher fidelity gravity model is necessary for Venusian aerobraking modeling, planning, and analysis.

Convection Cooling of Power Electronics Operating in Deep-Space

Abstract Since most traditional spacecraft are designed to operate in a vacuum environment, forced convection cooling has seen limited use in space-applications. This paper considers an ideal candidate–the Dragonfly Lander, a rotorcraft being sent into Deep-space to conduct experiments on Saturn's largest moon, Titan. A forced convection based thermal management solution is presented for the Rotor Drive Electronics (RDE) unit, a high-power electronics box responsible for controlling the rotors that allow the Lander to fly on Titan. A thermal flow model was built in Solidworks Flow Simulation to evaluate the effectiveness of a fan system integrated into the packaging design and used as the primary method for cooling the RDE. The model was validated with temperature data collected from custom designed ground support equipment. It was found that utilizing forced convection allows temperatures of the electronics within the tightly packaged RDE to remain within operational limits when conductive and radiative heat transfer alone are insufficient. Titan's dense atmosphere results in greater mass flow rates through fans compared to on Earth, making forced convection a particularly efficient method of heat transfer. This research may guide the use of forced convection in future space missions, or non-traditional environments.

Analysis of hovering flight stability of an insect-like flapping-wing robot in Martian condition

In efforts to search for life-form on a planet other than Earth, many projects have been launched to measure and analyze the surface and atmospheric conditions on Mars. To extend the exploration of Mars, scientists have attempted to perform flight in the extremely thin air environment of Mars. Inspired by the successful controlled flight of NASA's Helicopter on Mars, in this work, we investigate the six-degrees-of-freedom hovering flight dynamics of an insect-like flapping-wing robot, called KUBeetle. To hover the KUBeetle on Mars, using the scaling ratios of air density and gravity on Earth and Mars, we have found that the flapping frequency should be about 113.48 Hz, which is 4.93 times faster than that on Earth, and the required lift on Mars is about 38% of that on Earth. The computational fluid dynamics (CFD) analysis suggests that the lift produced by the flapping wings at the frequency on Mars is close to that predicted by the scaling ratios. A series of simulations are used to compute the stability derivatives to complete the equations of motion. The eigenvalue and eigenvector analyses have identified one fast subsidence mode, one slow subsidence mode, and one divergence oscillation mode in the longitudinal and lateral motions on Mars, which are identical to those on Earth. The dynamic responses of the robot under three initial disturbances in the translational speeds indicate that due to the 94% smaller real part of the complex roots in the divergence oscillation modes of the longitudinal and lateral motions on Mars, the growth of flight disturbances is much slower than on Earth. Therefore, the KUBeetle is capable of hovering flight on Mars, since it has enough time to use the feedback controls to stabilize the system. This work can be used to support the studies of the flight control of flapping wing robots in the Martian atmospheric condition, and to generalize such flight control for other non-terrestrial applications in the atmospheres of other planets and/or their moons.

Precision Mars Entry Navigation with Atmospheric Density Adaptation via Neural Networks

Spacecraft entering Mars require precise navigation algorithms capable of accurately estimating the vehicle’s position and velocity in dynamic and uncertain atmospheric environments. Discrepancies between the true Martian atmospheric density and the onboard density model can significantly impair the navigation performance. This work introduces a new approach to online filtering for Martian entry using a neural network to estimate atmospheric density and employing a “consider” analysis to account for the uncertainty in the estimate. The network is trained on an exponential atmospheric density model, and its parameters are dynamically adapted in real time to account for any mismatch between the true and estimated densities. The adaptation of the network is formulated as a maximum likelihood problem by leveraging the measurement innovations of the filter to identify optimal network parameters. Within the context of the maximum likelihood approach, incorporating a neural network enables the use of stochastic optimizers known for their efficiency in the machine learning domain. Performance comparisons are conducted against two online adaptive approaches, covariance matching and state augmentation and correction, in various realistic Martian entry navigation scenarios. The results show superior estimation accuracy compared to other approaches and precise alignment of the estimated density with a broad selection of realistic Martian atmospheres sampled from perturbed Mars Global Reference Atmospheric Model data.

The Feature Analysis and Modeling of Upper Atmospheric Midnight Density Maximum

The features of upper atmospheric midnight density maximum (MDM) around low geographic latitudes are studied based on neutral mass densities data at altitudes 360–480 km, derived from the accelerometer measurements aboard on the three polar orbiting satellites CHAMP (CHAllenging Minisatellite Payload), GRACE-A (Gravity Recovery and Climate Experiment-A), and SWARM-C (The Earth's Magnetic Field and Environment Explorers-C). The MDM appears during the local times from 23:00 to 02:00 LT (Local Time), whose peak locates at the low latitudes within 15∘ and two valleys locate at the middle latitudes between 35∘ and 45∘ on both hemispheres separately. The structure of MDM drifts toward the southern hemisphere overall. The MDM's amplitude decreases with increases in altitude and solar radiation level. The seasonal effect weakens the MDM's amplitudes around the summer and winter solstices, while the amplitudes around the spring and autumn equinoxes are extremely significant due to the slight seasonal difference between both hemispheres. Three atmospheric density models DTM2000 (Drag Temperature Model 2000), NRLMSISE00 (US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended atmosphere model), and JB2008 (Jacchia-Bowman 2008 model) are used to simulate the MDM along these three satellites' orbits, and compared with the observations. It is found that the JB2008 model is failed to describe the MDM, and the other two models underestimate the MDM's amplitudes at altitudes 360 km and 480 km: the simulated amplitudes by the DTM2000 model are 46% and 53% of the observed amplitudes, respectively, and only 33% and 26% for the NRLMSISE00 model. These three models are also failed to depict the MDM's variation with altitude, solar radiation level, and seasonal effects. In order to correct the model prediction, a 6th-order Legendre polynomial of geographic latitude, coupled with arguments of local time and altitude, is designed to fit the MDM signals from the three satellites' observations. In terms of amplitude and phase of the MDM, the fitting results agree with the observations very well, and the correlation coefficient is 0.923. It indicates that this empirical polynomial could be helpful to the density model correction and high accuracy prediction of spacecrafts in low Earth orbits.

Erythemal weighting function adjustment for a correct calculation of UV index in high-altitude cities

Abstract Andean cities are mostly characterized, and appreciated, by their high elevation. Commonly above 2500m above the sea level. However, a more subtle feature is their proximity to the Equator. These two characteristics provide these cities with unique climatological conditions. Complementary to this, the main autoethnography of the zone is “mestizo”, which is characterized by its type of skin (namely types III and IV). These kind of skins are highly adapted to radiation intensity (and atmosphere density) of the equatorial zone. We use measurements of radiation from sensors located at Quito in order to provide a novel method to computing the local ultraviolet-index range risk, taking into account an action spectrum of skin types III and IV, and the recommendations of the World Health Organization. The results of this study could be applied directly to cities with climatological conditions, and with population with skin types, similar to those from the Andean region.

First Observation of Harmonics of Magnetosonic Waves in Martian Magnetosheath Region

AbstractThe present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (fci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of fci. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left‐hand (LH), and higher frequency harmonics are associated with the right‐hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi‐perpendicular directions to the ambient magnetic field. The results of linear theory and Particle‐In‐Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.

Short-timescale Spatial Variability of Ganymede’s Optical Aurora

Ganymede’s auroras are the product of complex interactions between its intrinsic magnetosphere and the surrounding Jovian plasma environment and can be used to derive both atmospheric composition and density. In this study, we analyzed a time series of Ganymede’s optical auroras taken with Keck I/HIRES during eclipse by Jupiter on 2021 June 8 UTC, one day after the Juno flyby of Ganymede. The data had sufficient signal-to-noise in individual 5 minute observations to allow for the first high-cadence analysis of the spatial distribution of the optical aurora brightness and the ratio between the [O i] 630.0 and 557.7 nm disk-integrated auroral brightnesses—a quantity diagnostic of the relative abundances of O, O2, and H2O in Ganymede’s atmosphere. We found that the hemisphere closer to the centrifugal equator of Jupiter’s magnetosphere (where electron number density is highest) was up to twice as bright as the opposing hemisphere. The dusk (trailing) hemisphere, subjected to the highest flux of charged particles from Jupiter’s magnetosphere, was also consistently almost twice as bright as the dawn (leading) hemisphere. We modeled emission from simulated O2 and H2O atmospheres during eclipse and found that if Ganymede hosts an H2O sublimation atmosphere in sunlight, it must collapse on a faster timescale than expected to explain its absence in our data given our current understanding of Ganymede’s surface properties.

The Effectiveness of Sensor Visualizations and Graphic Augmentations for Detecting Vertical Obstacles

Slow or failed detection of low‐salience vertical obstacles and associated wires is one of today’s leading causes of fatal helicopter accidents. The risk of collisions with such obstacles is likely to increase as advanced aerial mobility and broadening drone activity promises to increase the density of air traffic at low altitudes, while growing demand for electricity and communication will expand the number of vertical structures. The current see‐and‐avoid detection paradigm relies on pilots to spend much of their visual attention looking outside for obstacles. This method is inadequate in low‐visibility conditions, cluttered environments, and given the need for pilots to engage in multiple competing visual tasks. With the expected growing number of hazards and an increased traffic volume, the current approach to collision avoidance will become even less tenable. A human‐in‐the‐loop helicopter simulator study was conducted to assess the effectiveness of sensor visualizations (image intensification or thermal imaging) and graphic augmentations (a bounding box around a tower and a circle surrounding the base of the tower) for supporting fast and reliable detection of vertical structures. Graphic augmentations resulted in faster tower detection time when ambient visibility and illumination were reduced close to the limit for visual flight. Bounding boxes around towers were detected first in all conditions but tended to mask the obstacle they were meant to highlight. Sensor visualization affected tower detection time only at night, where night vision goggles were more effective than the infrared thermal sensor.

Similarity solution for the magnetogasdynamic shock wave in a self-gravitating and rotating ideal gas under the influence of radiation heat flux

The Lie invariance method is used to analyze the one-dimensional, unsteady flow of a cylindrical shock wave in a rotating, self-gravitating, radiating ideal gas under the influence of an axial or azimuthal magnetic field, with an emphasis on adiabatic conditions. The analysis assumes a stationary environment just ahead of the shock wave and considers variations in fluid velocity, magnetic field, and density within the perturbed medium just behind the shock front. In the governing equations, the impact of thermal radiation under an optically thin limit is integrated into the energy equation. Utilizing the Lie invariance method, the set of partial differential equations governing the flow in this medium is transformed into a system of nonlinear ordinary differential equations (ODEs) using similarity variables. Two distinct cases of similarity solutions are obtained by selecting different values for the arbitrary constants associated with the generators. Among these cases, one yields similarity solutions assuming a power-law shock path and the other an exponential-law shock path. For both cases, the resulting set of nonlinear ODEs are numerically solved using the 4th-order Runge–Kutta method in MATLAB software. The article thoroughly explores the influence of various parameters, including γ (adiabatic index of the gas), Ma−2 (Alfvén–Mach number), σ (ambient density exponent), l1 (rotational parameter), and G0 (gravitational parameter) on the flow properties. The findings are visually presented to offer a comprehensive insight into the effects of these parameters.

Clinically-relevant reductions in oxygen partial pressure as possible contributor to cardiovascular benefits of sauna practice

The practice of sauna has been found to have both acute and long-term cardiovascular benefits, which are generally postulated to be a result of thermoregulatory physiological adaptations. Another element of sauna conditions which has been overlooked is that the extremely high absolute water content of air at sauna temperature, even at low relative humidity, results in significantly decreased partial pressure of oxygen. Using the Arden-Buck equation for water-carrying capacity of air along with the barometric formula, it is shown in this hypothesis that typical sauna conditions have an oxygen partial pressure reduction that may be equivalent to significant elevations above sea level. This effect may also be enhanced by lower air density further reducing available oxygen relative to respiratory volume.This paper presents the hypothesis that altitude adaptation may be a contributing factor in the cardiovascular benefits of sauna treatments, suggesting that sauna should be considered as an alternative in instances where intermittent hypoxic training is indicated but not available, and that clinical research into sauna treatment is merited for conditions in which intermittent hypoxic training is known to have applications. The hypothesis could be investigated through pulse oximetry of subjects under sauna conditions and by tracking blood markers of altitude adaptation compared to a control group using steam rooms.

DETERMINING THE DENSITY AND MOLAR MASS OF AIR IN A HOME EXPERIMENT

Formulation of the problem. Experimental research is an integral part of physics education. During distance learning, students can carry out hands-on experiments only at home. Modern smartphones, equipped with various sensors, offer significant capabilities for this purpose. The literature offers quite extensive descriptions of experiments aimed at determining mechanical, acoustic, and optical quantities using smartphones. At the same time, insufficient attention has been paid to determining gas parameters that can be measured using the pressure sensor embedded in smartphones. Therefore, the relevant task is to develop a methodology for experimenting to determine the density of air and its molar mass at home using a pressure sensor. Materials and methods. To achieve the objective of the study, we used the analysis of the curriculum of the course "General Physics for Bachelor of Engineering", a review of the methodological instructions for performing laboratory work in the section "Molecular Physics and Thermodynamics" of the physics course of technical universities, a review of the literature on the topic of the study, and an analysis of the results of student research on the dependence of air pressure on altitude. We also surveyed students about the possibility of conducting the research at home and their interest in conducting other experiments using a smartphone. Results. The methodology for determining the density and molar mass of air was developed based on the results of a study of the pressure-height dependence. It is shown that it is necessary to perform statistical processing of experimental data to estimate the sought quantities. The experimental results allowed us to obtain values of density and molar mass of air that show a good correlation with the tabulated values. Conclusions. Studying the pressure-altitude relationship using a smartphone and the PhyPhox application allows for fairly accurate calculations of air density and molar mass. According to the survey results, students responded positively to conducting home experiments using smartphones.

Assessing the possibility of using a variable-length launch vehicle with a polymer body for orbiting payload

The object of this study was the motion of an ultralight class variable-length launch vehicle made of a polymer body along the active phase of the trajectory. The work considers the solution to the problem of designing low-cost means of delivery to orbit, namely to the assessment of the possibility of removing the payload by a carrier rocket with a polymer body of variable length beyond the dense atmosphere of the Earth. For this purpose, ballistic projection of the trajectory of the launch vehicle was carried out taking into account overloading; its aerodynamic characteristics and peculiarities of aerothermodynamic processes occurring during flight in the atmospheric phase of the trajectory were determined. The closeness (up to 10 %) of the obtained results with known experimental data is shown. The influence of the aerodynamic force on the parameters of the launch vehicle motion was studied. A flight simulation was conducted, the results of which showed the fundamental possibility of launching a CubeSat 24U class payload using a launch vehicle with a polymer body of variable length to a suborbital trajectory with an altitude of about 300 km. At the same time, the effective longitudinal overload on the body of the launch vehicle does not exceed 4 units, and the temperature on the surface of the body does not exceed 300 K. A feature of the research is the use of a multidisciplinary approach, which implies taking into account the interrelationship of aerodynamic, thermodynamic, and ballistic processes. The established motion parameters, aerodynamic characteristics, and the surface heating temperature of the launch vehicle body are key values for further research on the design and analysis of a launch vehicle with a polymer body of variable length. These data could be used to calculate the mechanical and thermal loads acting on the structure of the launch vehicle during flight

Dust model sensitivity to dust source mask, sandblasting efficiency, air density, and land use: Implications for model improvement

This study compares dust storm simulations using two commonly adopted methods for representing four important dust emission parameters. Compared with a dynamic dust source mask based on land use and vegetation cover, a static mask based solely on land use overestimates dust concentration and optical depth by a factor of 2, besides generating spurious emissions. The results reinforce that seasonal variations in vegetation cover can significantly affect dust emissions. For sandblasting efficiency, a clay-dependent semiempirical expression produces 12 times more dust than does a physics-based expression. Simulations using model-predicted versus constant air density differ by only 8%. However, this difference (often overlooked) could range between 12% and 22% for annual simulations over global dust source regions. Simulations with updated versus old land use data, using the same dust source mask, differ twofold, indicating the significant impact of land use change on regional dust emission in central Arizona. The difference between simulations within each of the four pairs is generally larger than the uncertainty due to meteorology. The simulations align better with observation when using the dynamic dust source mask, the physics-based sandblasting efficiency, and the up-to-date land use data. Given the high sensitivity of dust to surface conditions, the results discussed have implications for improving the dust cycle in weather and climate models and for interpreting model intercomparisons.

Hyperbolic high-fidelity simulations of cratering on a particle bed induced by a turbulent supersonic plume

A recently proposed hyperbolic granular model (Balakrishnan and Bellan, 2024) has been used to investigate the problem of supersonic-jet induced cratering on a solid-particle bed. This model relies upon the concept of added mass and a fluid-mediated particle pressure to render the system of equations hyperbolic. The jet is modeled using Large Eddy Simulation (LES) and the solid phase is modeled in an Eulerian framework using a Kinetic-Theory-based model modified for dense particle collections. The formulation also incorporates pseudo-turbulent kinetic energy (PTKE) which has been shown to modify a flow field laden with particles. The results explore the influence of the jet-to-ambient fluid density ratio, of the ambient fluid density, and of PTKE. A detailed analysis of the local and time-wise evolution of the added mass is presented through quantification of convection, added mass source and velocity-difference contributions. A quantitative assessment of the PTKE equation shows that while production is mostly effective at the crater base and walls, the dissipation and source term, both of which are also effective in the ejecta, nearly balance each other. The influence of the PTKE is mostly observed in the dilute particle regions (soil/gas interface and ejecta), with no effect on the macroscopic length scales of the flow. Both the jet-to-ambient fluid density ratio and the ambient fluid density affect the macroscopic crater features through entertainment into the jet that is determined by the former, and through the density of the fluid entrained, determined by the latter. This complex interaction governs the evolution of the crater diameter, visible top-view depth, and lower depth of the compacted region.