Surface Quantities Research Articles

The impact of the length-to-depth ratio on aerodynamic surface quantities of a rarefied hypersonic cavity flow

A computational investigation has been carried out to examine a non-reacting rarefied hypersonic flow over cavities by employing the Direct Simulation Monte Carlo (DSMC) method. The work focuses on the effects on the aerodynamic surface quantities due to variations in the cavity length-to-depth (L/H) ratio. The results highlight the sensitivity of the heat transfer, pressure and skin friction coefficients due to changes to the cavity L/H ratio. The L/H ratio ranged from 1 to 4, which corresponds to the transition flow regime based on an overall Knudsen number KnL. The analysis showed that the aerodynamic quantities acting on the cavity surface rely on the L/H ratio. It was found that pressure load and heating load to the cavity surfaces presented peak values along the forward face, more precisely in the vicinity of the cavity shoulder. Moreover, these loads are much higher than those found in a smooth surface, for the conditions investigated.

Prediction of groundwater levels from lake levels and climate data using ann approach

There are many environmental concerns relating to the quality and quantity of surface and groundwater. It is very important to estimate the quantity of water by using readily available climate data for managing water resources of the natural environment. As a case study an artificial neural network (ANN) methodology is developed for estimating the groundwater levels (upper Floridan aquifer levels) as a function of monthly averaged precipitation, evaporation, and measured levels of Magnolia and Brooklyn Lakes in north-central Florida. Groundwater and surface water are highly interactive in the region due to the characteristics of the geological structure, which consists of a sandy surficial aquifer, and a highly transmissive limestone confined aquifer known as the Floridan aquifer system (FAS), which are separated by a leaky clayey confining unit. In a lake groundwater system that is typical of many karst lakes in Florida, a large part of the groundwater outflow occurs by means of vertical leakage through the underlying confining unit to a deeper highly transmissive upper Floridan aquifer. This provides a direct hydraulic connection between the lakes and the aquifer, which creates fast and dynamic surface water / groundwater interaction. Relationships among lake levels, groundwater levels, rainfall, and evapotranspiration were determined using ANN-based models and multiple-linear regression (MLR) and multiple-nonlinear regression (MNLR) models. All the models were fitted to the monthly data series and their performances were compared. ANN-based models performed better than MLR and MNLR models in predicting groundwater levels.

Computational Analysis of a Rarefied Hypersonic Flow over Backward-Facing Steps

This work deals with a numerical study on backward-facing steps situated in a nonreacting low-density hypersonic flow. The work is motivated by the interest in investigating the impact on the aerodynamic surface quantities of surface discontinuities on hypersonic vehicles. Discontinuities are represented by backward-facing steps with boundary-layer thickness larger than the step height at the step position. The primary emphasis is to assess the sensitivity of the heat transfer, pressure, and skin friction coefficients. In doing so, these effects have been investigated by employing the direct simulation Monte Carlo (DSMC) method. The analysis showed that the flow past a backward-facing step in hypersonic flow is characterized by a strong expansion on the corner of the step, which influences the downstream separation region and the aerodynamics surface properties downstream of the back face. It was found that the recirculation region behind of the steps is a function of the back-face height, for the conditions investigated. In addition, the heat flux to the surface and the wall pressure increased in the reattachment zone downstream of the back face and reached the flat plate values in a smooth fashion. A comparison of the present simulation results with experimental data showed close agreement concerning the heat flux to step surface.

Electrodeposition of CeO2 and Pd-CeO2 on small pore size metallic foams: Selection of deposition parameters

The electrodeposition, in particular the electro-base generation method, is an alternative to conventional washcoating to coat open-cell metallic foams, especially small pore size ones. In this work, the method was applied for the in-situ synthesis of cerium-based coatings, CeO2 and Pd-CeO2, on 100 pores per inch (ppi) FeCrAl foams. The range of parameters suitable for the electrodeposition of CeO2 films of different thickness and morphology was firstly investigated, i.e. Ce(NO3)3 concentration, potential applied, and deposition time. Then the most challenging one step Pd-CeO2 electrodeposition was studied; the Pd content and distribution were optimized considering also the electrochemistry and chemistry of Pd2+ species, i.e. by selection of a suitable Pd2+ complex precursor (Pd(NH3)4(NO3)2 or PdCl2 in HCl). Coated foams were calcined at 550 °C to obtain the structured catalysts. The CO oxidation was used as a model reaction to test the activity of Pd-CeO2 catalysts.The electrodeposition of cubic fluorite CeO2 coatings on the surface of the foam ranging from few to 18 μm and made by compact and/or platelet particles was easily achieved and with a high reproducibility. The Pd-CeO2 samples prepared from the ammine-containing electrolyte, though generated a well-adhered coating, resulted in a lower Pd content than the nominal value of the electrolyte. A high electrolyte concentration containing PdCl2 combined with a short time allowed to deposit a rather thick Pd-containing CeO2 coating avoiding the massive Pd° deposition. CO oxidation tests, especially at high flow rates, confirmed the key role of the coating and Pd distribution on the activity of the structured catalysts. A comparison of the conversion in mass transfer regime and estimates with literature correlations was presented, showing that, despite the very complex geometry of the support, a remarkably high quantity of the available surface is effectively exploited, paving the way for compact catalytic converters.

Investigation on wall shear stress measurement in supersonic flows with shock waves using shear-sensitive liquid crystal coating

Wall shear stress (skin friction) is one of the fundamental surface quantities in aerodynamics but its measurement remains challenging. This paper studies the measurement of wall shear stress vector fields in supersonic flows with shock waves using the shear-sensitive liquid crystal coating (SSLCC) technique. A previously developed SSLCC technique was improved and used for the measurement of wall shear stresses in a supersonic jet flow. Experimental results show that the flow structures including shock waves in the supersonic jet flow were visualized by the SSLCC technique; furthermore, the shear stress vector field over a planar surface induced by the supersonic jet flow was measured by the SSLCC technique. The shock waves and the compression-expansion repetitions in the supersonic jet flow were captured, respectively, by analysing the shear direction field and the skin friction line pattern. This work demonstrates the capabilities of the SSLCC technique to visualize and measure wall shear stresses in supersonic flows with complex shock waves.

Application of Natural Water Retention Measures in Flood Management

Due to climate change, increasingly extreme weather conditions and runoff parameters are leading to the enhancement of flood risk. The increasing probability of fast flowing, high intensity flash floods jeopardize both the residents of small municipalities and the fields of farmers, especially in the downstream areas of mountainous and hilly regions. In many cases the protection of settlements cannot be solved through conventional flood management approaches due to high investment costs and built-in floodplains. The main goal of this article is to analyse the potential of flood risk mitigation with applying natural water retention measures. These additional measures could have a positive effect on the quality and quantity of surface and groundwater. Research results facilitate an even more effective preparation in a way of applying nature based solutions to supplement traditional flood management.

Satellite and In Situ Observations for Advancing Global Earth Surface Modelling: A Review

In this paper, we review the use of satellite-based remote sensing in combination with in situ data to inform Earth surface modelling. This involves verification and optimization methods that can handle both random and systematic errors and result in effective model improvement for both surface monitoring and prediction applications. The reasons for diverse remote sensing data and products include (i) their complementary areal and temporal coverage, (ii) their diverse and covariant information content, and (iii) their ability to complement in situ observations, which are often sparse and only locally representative. To improve our understanding of the complex behavior of the Earth system at the surface and sub-surface, we need large volumes of data from high-resolution modelling and remote sensing, since the Earth surface exhibits a high degree of heterogeneity and discontinuities in space and time. The spatial and temporal variability of the biosphere, hydrosphere, cryosphere and anthroposphere calls for an increased use of Earth observation (EO) data attaining volumes previously considered prohibitive. We review data availability and discuss recent examples where satellite remote sensing is used to infer observable surface quantities directly or indirectly, with particular emphasis on key parameters necessary for weather and climate prediction. Coordinated high-resolution remote-sensing and modelling/assimilation capabilities for the Earth surface are required to support an international application-focused effort.

Variability in obsidian structural water content and its importance in the hydration dating of cultural artifacts

The process of dating ancient obsidian artifacts converts the quantity of surface diffused molecular water to a calendar age using an experimentally derived diffusion coefficient predicted from glass composition. The internal structural water content of rhyolitic obsidian has been identified as a highly influential variable that controls the rate of water diffusion at ambient temperature. We demonstrate through the use of infrared spectroscopy and specific gravity (density) measurements on samples from 34 obsidian sources that total structural water (H2Ot) concentrations between sources can range from 0.07% to 1.66%. Structural water concentration within individual sources may also vary significantly and impact the accuracy of estimated ages for artifact manufacture if not properly monitored. A calibration for the water determination on individual samples by density measurement is developed here and the impact of structural water variation on obsidian chronometric dates is discussed.

NTBC and MTT Reduction Electrochemistry: Impact on Cu Superconformal Plating for Fabrication of Glass Interposers

Nitro blue tetrazolium chloride (NTBC) and thiazolyl blue tetrazolium bromide (MTT) are the organic additives applied successfully in Cu superconformal filling of through glass vias (TGVs) with aspect ratios 6:1 and 10:1. However, traces of purple inclusion were observed through the cross-sectioning of electroplated samples indicating that a reduction could likely be occurring during the plating process. In this work, the reduction propensity of NTBC and MTT in the course of Cu superconformal plating was assessed in the absence of Cu(II) ions by cyclic voltammetry, controlled-potential electrolysis (CPE), and UV-Vis spectroscopy. A CPE potential of −0.25 V vs Ag/AgCl reference electrode was selected aiming at studying the reduction process as close as possible to the actual potential range of Cu deposition. The CPE and UV-Vis results suggest that both additives reduce steadily with time generating different (by)products. Also, it is shown that the MTT reduces itself at a rate that is substantial at lower pH, producing both surface precipitates and soluble reduction products. Unlike that, the NTBC reduction exhibits weaker pH dependence and generates lower quantity of surface precipitates only. Thus, the reduction of MTT is expected to impact considerably stronger than NTBC the Cu superconformal plating process in TGVs.

A new hypothesis on the role of vessel topology in cerebral aneurysm initiation

Aneurysm pathogenesis is thought to be strongly linked with hemodynamical effects. According to our current knowledge, the formation process is initiated by locally disturbed flow conditions. The aim of the current work is to provide a numerical investigation on the role of the flow field at the stage of the initiation, before the aneurysm formation. Digitally reconstructed pre-aneurysmal geometries are used to examine correlations of the flow patterns to the location and direction of the aneurysms formed later. We argue that a very specific rotational flow pattern is present in all the investigated cases marking the location of the later aneurysm and that these flow patterns provide the mechanical load on the wall that can lead to a destructive remodelling in the vessel wall. Furthermore, these patterns induce elevated vessel surface related variables (e.g. wall shear stress (WSS), wall shear stress gradient (WSSG) and oscillatory shear index (OSI)), in agreement with the previous findings. We emphasise that the analysis of the flow patterns provides a deeper insight and a more robust numerical methodology compared to the sole examination of the aforementioned surface quantities.

Active lens for thermal aberration compensation in lithography lens.

High laser absorption and strong resolution enhancement technology make thermal aberration control of lithography lenses more challenging. We present an active lens that uses four bellows actuators to generate astigmatism (Z5) on the lens surface. The apparatus utilizes optical path difference to compensate the system wavefront. In order to assess the specifications of the compensator, the finite element method and experimental analyses are carried out to obtain and validate the general properties of the apparatus. The results show that the Z5 deformation quantity of lens's upper surface exceeds 600nm; further, Z5 coefficient accuracy is better than ±1 nm. The apparatus can be an efficient compensator for thermal aberration compensation, especially aberration caused by the dipole illumination.

Amorphous Phosphorus-Doped Cobalt Sulfide Modified on Silicon Pyramids for Efficient Solar Water Reduction.

Cobalt sulfide (CoS x) functioned as a co-catalyst to accelerate the kinetics of photogenerated electrons on Si photocathode, leading to the enhancement of solar hydrogen evolution efficiency. By doping phosphorus heteroatoms, CoS x materials showed an improved catalytic activity because of superior surface area and quantity of active sites. Furthermore, increased vacancies in unoccupied electronic states were observed, as more phosphorus atoms doped into CoS x co-catalysts. Although these vacant sites improved the capability to accept photoinduced electrons from Si photoabsorber, chemisorption energy of atomic hydrogen on catalysts was the dominant factor affecting in photoelectrochemical performance. We suggested that P-doped CoS x with appropriate doping quantities showed thermoneutral hydrogen adsorption. Excess phosphorus dopants in CoS x contributed to excessively strong adsorption with H atoms, causing the poor consecutive desorption ability of photocatalytic reaction. The optimal P-doped CoS x-decorated Si photocathode showed a photocurrent of -20.6 mA cm-2 at 0 V. Moreover, a TiO2 thin film was deposited on the Si photocathode as a passivation layer for improving the durability. The current density of 10 nm TiO2-modified photocathode remained at approximately -13.3 mA cm-2 after 1 h of chronoamperometry.

Assessment of film cooling’s surface quantities using pressure- and temperature-sensitive paint: Comparisons between shaped and sand-dune inspired holes

Following the previous work (Zhou and Hu, 2017), a comprehensive assessment was performed to further evaluate the film cooling’s surface quantities behind shaped and sand dune-inspired holes. Adiabatic film cooling effectiveness, heat transfer coefficient, and net heat flux reduction (NHFR) were measured at four blowing ratios (M = 0.40, 0.90, 1.40, and 2.00). The measured quantities were compared side-by-side between the shaped and sand dune-inspired holes. The pressure-sensitive paint (PSP) technique was used to acquire high-resolution adiabatic effectiveness and the temperature-sensitive paint (TSP) technique was used to map the corresponding heat transfer coefficient over the surface. Nitrogen and air, with a density ratio of about one, were used as the coolant for the PSP and TSP tests respectively. The measured results showed that the adiabatic effectiveness of the Barchan dune-shaped injection compound (BDSIC) was significantly higher than that of the shaped hole. Improvements of 20–150% in the centerline and 30–400% in the laterally averaged effectiveness were observed behind the BDSIC compared to the shaped hole. As for the heat transfer performance, although the BDSIC showed 10–20% higher heat transfer coefficient, hf/h0, the measured spatially averaged NHFR still demonstrated an augmentation of 50–150% in heat flux reduction in comparison to the shaped hole. This paper represents the first effort to comprehensively evaluate the surface quantities behind BDSIC film cooling concept using both PSP and TSP techniques.

Modeling the Atomic-to-molecular Transition in Cosmological Simulations of Galaxy Formation

Abstract Large-scale cosmological simulations of galaxy formation currently do not resolve the densities at which molecular hydrogen forms, implying that the atomic-to-molecular transition must be modeled either on the fly or in postprocessing. We present an improved postprocessing framework to estimate the abundance of atomic and molecular hydrogen and apply it to the IllustrisTNG simulations. We compare five different models for the atomic-to-molecular transition, including empirical, simulation-based, and theoretical prescriptions. Most of these models rely on the surface density of neutral hydrogen and the ultraviolet (UV) flux in the Lyman–Werner band as input parameters. Computing these quantities on the kiloparsec scale resolved by the simulations emerges as the main challenge. We show that the commonly used Jeans length approximation to the column density of a system can be biased and exhibits large cell-to-cell scatter. Instead, we propose to compute all surface quantities in face-on projections and perform the modeling in two dimensions. In general, the two methods agree on average, but their predictions diverge for individual galaxies and for models based on the observed midplane pressure of galaxies. We model the UV radiation from young stars by assuming a constant escape fraction and optically thin propagation throughout the galaxy. With these improvements, we find that the five models for the atomic-to-molecular transition roughly agree on average but that the details of the modeling matter for individual galaxies and the spatial distribution of molecular hydrogen. We emphasize that the estimated molecular fractions are approximate due to the significant systematic uncertainties.

Ce and Zr Modified WO3-TiO2 Catalysts for Selective Catalytic Reduction of NOx by NH3

A series of Ce and/or Zr modified WO3-TiO2 catalysts were synthesized by the impregnation method, which were employed for NH3-SCR reaction. The T50 contour lines of NOx were used to quickly optimize catalyst composition, the Ce20Zr12.5WTi catalyst was considered to be the optimization result, and also exhibited excellent NH3-SCR activity and thermal stability with broad operation temperature window, which is a very promising catalyst for NOx abatement from diesel engine exhaust. The excellent catalytic performance is associated with the formation of Ce-Zr solid solution. The introduction of Zr to CeWTi catalyst facilitated the redox of Ce4+/Ce3+ and the formation of more acid sites, more Ce3+ ions, more oxygen vacancies, larger quantities of surface adsorbed oxygen species and NH3, which were beneficial for the excellent selective catalytic reduction (SCR) performance.

Quantity and Quality of Surface and Subsurface Runoff from an Eroded Loess Slope Used for Agricultural Purposes

The purpose of the work was to determine the surface and subsurface water runoff and selected constituents of the matter contained and carried out from the eroded loess slope used as arable land. The research was carried out in 2008–2011 on the Lublin Upland. The quantity of water flowing out of the slope was measured and samples were collected in order to determine the concentration of the soil suspension of nitrogen and its forms as well as phosphorus and potassium. Soil tests were also carried out and the rainfall amount and intensity was monitored. The research results show that the amount of precipitation was significantly statistically correlated with the quantity of surface and subsurface water runoff and with the precipitation and surface runoff erosion indicator EI30 (correlations at the level of r = 0.75–0.78). In addition, the mass of eroded soil was strongly correlated with the erosion indicator of rain and surface runoff EI30 (r = 0.86). The annual soil losses were from 21.1 to 173.1 Mg ha−1. The concentration of chemical components dissolved in the surface and subsurface runoff water in most cases proved to be negatively statistically correlated with the amount of precipitation and indicator EI30. The correlation coefficients (r) were at levels from −0.32 to −0.52. The annual loss of nutrients caused by chemical erosion was: nitrogen 7.210–29.949 kg ha−1, phosphorus 0.846–5.279 kg ha−1 and potassium 7.065–21.660 kg ha−1. The highest intensity of water erosion was recorded in 2010, when root crops were grown in the field.

Conservation of Ground Water at Maheshtala Bleaching and Dyeing Cluster, a Populated Area in West Bengal, India by Implementing Ultra filtration and Reverse Osmosis Based Effluent Treatment Plant—A Case Study

The present study endeavors to assess the quantity and nature of effluents generated from textile bleaching and dyeing units in Maheshtala cluster, West Bengal, India and to provide a treatment process to conserve groundwater resources. Installation of decentralized common effluent treatment plants (CETP) with advanced membrane based treatment system will save ground water which can be reused. Effluent discharged from medium, small and tiny units of this cluster estimated at 20,000 KLD lifted through pumps from groundwater aquifer. Studies in Kalikapur area under Maheshtala cluster during 2012–2016 showed following mean concentrations of various physico-chemical variables: pH (7.29), BOD (150 mg/l), COD (457 mg/l), TDS (3534 mg/l), TSS (108 mg/l)) and metals such as Cd (0.02 mg/l), Pb (0.20 mg/l), Cr (0.21 mg/l), Fe (1.69 mg/l) and Na (2367 mg/l). These values exceeded the standard permissible limits stipulated by IS: 10500 (2012) and WHO (2003). Due to absence of CETPs in the cluster wastewater laden with toxic trace metals affects the environment and human health, degrades the quantity and quality of both surface and groundwater, contaminates agricultural land, crops, fruits and vegetables, and causes harm to aquatic life forms. Four to five decentralized CETPs are required to install at different locations of the Mahestala region with a capacity of 5000 KLD each, at least one in Kalikapur area, to purify large volume of wastewater (20,000 KLD) and to produce reusable groundwater to an extent of 11,000 KLD (55%) in a populated urban area at Maheshtala near Calcutta, a leading city of India. Further, population and textile bleaching and dyeing industries in last 10 years are increasing. The reuse of wastewater is inevitable as rainfall is decreasing in last 10 years and a result the groundwater recharge is also decreasing as per West Bengal Statistical Handbook 2014.

A Contribution for the Assessment of Discretization Error Estimators Based on Grid Refinement Studies

This paper presents grid refinement studies for statistically steady, two-dimensional (2D) flows of an incompressible fluid: a flat plate at Reynolds numbers equal to 107, 108, and 109 and the NACA 0012 airfoil at angles of attack of 0, 4, and 10 deg with Re = 6 × 106. Results are based on the numerical solution of the Reynolds-averaged Navier–Stokes (RANS) equations supplemented by one of three eddy-viscosity turbulence models of choice: the one-equation model of Spalart and Allmaras and the two-equation models k – ω SST and k−kL. Grid refinement studies are performed in sets of geometrically similar structured grids, permitting an unambiguous definition of the typical cell size, using double precision and an iterative convergence criterion that guarantees a numerical error dominated by the discretization error. For each case, different grid sets with the same number of cells but different near-wall spacings are used to generate a data set that allows more than one estimation of the numerical uncertainty for similar grid densities. The selected flow quantities include functional (integral), surface, and local flow quantities, namely, drag/resistance and lift coefficients; skin friction and pressure coefficients at the wall; and mean velocity components and eddy viscosity at specified locations in the boundary-layer region. An extra set of grids significantly more refined than those proposed for the estimation of the numerical uncertainty is generated for each test case. Using power law extrapolations, these extra solutions are used to obtain an approximation of the exact solution that allows the assessment of the performance of the numerical uncertainty estimations performed for the basis data set. However, it must be stated that with grids up to 2.5 (plate) and 8.46 (airfoil) million cells in two dimensions, the asymptotic range is not attained for many of the selected flow quantities. All this data is available online to the community.

Particle simulation of nonequilibrium gas flows based on ellipsoidal statistical Fokker–Planck model

In order to improve the efficiency of particle simulation method for gas flows spanning the rarefied and continuum regimes, one promising approach is to employ the Fokker–Planck-type gas kinetic model. The ellipsoidal statistical Fokker–Planck (ES-FP) model treats the evolution of individual molecular velocity as a continuous stochastic process, which can be equivalently described by the Langevin dynamics where the forces acting on each gas molecule are a linear drag force and an anisotropic fluctuating force. By utilizing the exact stochastic integral solution of the corresponding Langevin equation, the ES-FP model is numerically implemented in a particle Monte Carlo manner. In a validation of the particle scheme, excellent agreement is obtained between the simulation results and the analytical solution for the same initial-value problem of ES-FP equation. The ES-FP particle method is used to simulate the relaxation process in a nonequilibrium gas, and agrees well with the direct simulation Monte Carlo (DSMC) method in the predictions of viscous stress and heat flux. Furthermore, extensive ES-FP particle simulations are performed for Couette flows at different Knudsen numbers ranging from 0.001 to 10, as well as supersonic flat-plate flows at different Knudsen numbers ranging from 0.001 to 0.1. Both flow fields and surface quantities are investigated and compared with the DSMC or theoretical solutions. In the ES-FP simulations, the Prandtl number of gas can be corrected, and the physical behaviors in different flow regimes can be properly captured. With reasonable agreement between the ES-FP and DSMC results, the ES-FP simulation is found to be more efficient than DSMC and can significantly save memory cost and CPU time, especially for multi-dimensional flows in the low-Knudsen-number regime.

Polynomial conserved quantities of Lie applicable surfaces

Using the gauge theoretic approach for Lie applicable surfaces, we characterise certain subclasses of surfaces in terms of polynomial conserved quantities. These include isothermic and Guichard surfaces of conformal geometry and L-isothermic surfaces of Laguerre geometry. In this setting one can see that the well known transformations available for these surfaces are induced by the transformations of the underlying Lie applicable surfaces. We also consider linear Weingarten surfaces in this setting and develop a new Bäcklund-type transformation for these surfaces.