Evolution Of Surface Pressure Research Articles

Critical indicators of dynamic stall vortex

During a dynamic stall process, various flow structures leave their pressure footprints on a wing surface, through which it is possible to understand the development of different flow stages and predict the critical flow events. Based on a classical airfoil ramp-up pitching motion, proper orthogonal decomposition analysis of pressure on the suction surface is carried out in this study. Accordingly, the surface pressure evolution during dynamic stall is summarized into three basic physical schemas, based on which several real-time critical indicators for predicting the flow events related to the dynamic stall vortex (DSV) are constructed. These critical indicators include the spatial distribution coefficient of pressure (SDCP), the high-order central moment of pressure (HCMP), the location of peak pressure (LPP) and the modulated location of peak pressure (MLPP). These indicators can predict the formation of laminar separation bubbles, DSV initiation, DSV centre position and the detachment of DSV. Therefore, the real-time whole-life monitoring of DSV has been realized. Moreover, the effectiveness of these indicators has also been confirmed under different parameters, and testing using wind tunnel experimental data proves their noise robustness. Studies show that the SDCP and HCMP may also be effective even if only two transducers are used. Finally, a modification method of SDCP based on Z-score standardized pressure is proposed. It is found that the modified SDCP can effectively reduce sensitivity to kinematic parameters and the Reynolds number. The critical indicators in this study can be used as a reference for the standardized mathematical and physical description of DSV evolution, thus laying a foundation for constructing a universal theoretical framework of dynamic stall.

Volatile transport modeling on Triton with new observational constraints

Neptune's moon Triton shares many similarities with Pluto, including volatile cycles of N2, CH4 and CO, and represents a benchmark case for the study of surface-atmosphere interactions on volatile-rich Kuiper Belt objects. The observations of Pluto by New Horizons acquired during the 2015 flyby and their analysis with volatile transport models (VTMs) shed light on how volatile sublimation-condensation cycles control the climate and shape the surface of such objects. Within the context of New Horizons observations as well as recent Earth-based observations of Triton, we adapt a Plutonian VTM to Triton, and test its ability to simulate its volatile cycles, thereby aiding our understanding of its climate.Here we present numerical VTM simulations exploring the volatile cycles of N2, CH4 and CO on Triton over long-term and seasonal timescales (cap extent, surface temperatures, surface pressure, sublimation rates) for varying model parameters (including the surface ice reservoir, albedo, thermal inertia, and the internal heat flux). We explore what scenarios and model parameters allow for a best match of the available observations. In particular, our set of observational constraints include Voyager 2 observations (surface pressure and cap extent), ground-based near-infrared (0.8–2.4 μm) disk-integrated spectra (the relative surface area of volatile vs. non-volatile ice) and the evolution of surface pressure as retrieved from stellar occultations.Our results show that Triton's poles act as cold traps for volatile ices and favor the formation of polar caps extending to lower latitudes through glacial flow or through the formation of thinner seasonal deposits. As previously evidenced by other VTMs, North-South asymmetries in surface properties can favor the development of one cap over the other. Our best-case simulations are obtained for a bedrock surface albedo of 0.6–0.7, a global reservoir of N2 ice thicker than 200 m, and a bedrock thermal inertia larger than 500 SI (or smaller but with a large internal heat flux). The large N2 ice reservoir implies a permanent N2 southern cap (several 100 m thick) extending to the equatorial regions with higher amounts of volatile ice at the south pole, which is not inconsistent with Voyager 2 images but does not fit well with observed full-disk near-infrared spectra. Our results also suggest that a small permanent polar cap exists in the northern (currently winter) hemisphere if the internal heat flux remains relatively low (e.g. radiogenic, < 3 mW m−2). A non-permanent northern polar cap was only obtained in some of our simulations with high internal heat flux (30 mW m−2). The northern cap will possibly extend to 30°N in the next decade, thus becoming visible by Earth-based telescopes. On the basis of our model results, we also discuss the composition of several surface units seen by Voyager 2 in 1989, including the bright equatorial fringe and dark surface patches.Finally, we provide predictions for the evolution of ice distribution, surface pressure and CO and CH4 atmospheric mixing ratios in the next decades. According to our model, the surface pressure should slowly decrease but remain larger than 0.5 Pa by 2060. We also model the thermal lightcurves of Triton for different climate scenarios in 2022, which serve as predictions for future James Webb Space Telescope observations.

Lower atmosphere and pressure evolution on Pluto from ground-based stellar occultations, 1988–2016

Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. Aims. The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. Methods. Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 μbar to 10 nbar). Results. (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4–7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.

Multiscale approach to characterize bulk, surface and foaming behavior of casein micelles as a function of alkalinisation

Caseins display the major protein fraction in milk, and thus, significantly impact on milk's techno-functional properties such as foaming. As the micellar structure is mainly stabilized by hydrophobic as well as electrostatic forces, a gradual increase in pH value from 6.0 to 11.0 induced pronounced structural modifications. In consequence of alkalinisation, micelle size and composition changed. This had an impact on the solution properties such as turbidity. Furthermore, interfacial characteristics, e.g. surface pressure evolution and surface dilatational properties were affected. Different situations occurred regarding interfacial covering, which was also reflected in the resulting foam structures. The highest foam stability was obtained for pH 9.0. At this pH, highly voluminous casein micelles combined with a considerable amount of serum casein formed maximal viscoelastic surface layers. Micelle dissociation reduced viscoelasticity as well as foam stability, whilst drainage increased.

Temporal and spatial evolution of an on‐land hurricane observed by seismic data

AbstractA dense seismic array can provide new perspectives for a decaying hurricane after its landfall. The case of Hurricane Isaac in 2012 is presented using a seismic array from EarthScope (USArray). The amplitude‐distance plots from the center of the hurricane showed a sharp peak at a distance of 75 km at the time of landfall. This peak decayed and moved outward from the center over the next 1.5 days. The sharp peak can be explained by strong surface pressure fluctuations under the eyewall in which a focused ascending flow is known to exist. We reconstructed the time evolution of surface pressure that explains seismic data. Pressure solutions indicate that the eyewall stayed at 75 km in the first 10 h after the landfall, while the ascending flow weakened significantly. In the following 24 h, the eyewall diffused and moved to distances about 200–300 km, suggesting its collapse during this period.

Convective activity over heat-low region and Indian summer monsoon rainfall during contrasting phases of ESI tendency

In this paper, the changes in convective activity over heat-low region over northwest India during contrasting phases of effective strength index (ESI) tendency have been examined. During contrasting phases of ESI tendency, evolution of surface pressure and temperature field over India from winter to spring is exactly opposite, and hence, the heat-low over northwest India depicts temporal and spatial variations in magnitude and location. During positive ESI tendency, the evolution of surface cooling and high surface pressure from winter to spring suggests reduced convective activity over heat-low region, while during the negative phase of ESI tendency, anomalously warm surface temperatures and low surface pressure evolve from winter to spring suggesting enhanced convective activity over the heat low region. The temporal variability in the relationship between surface temperature/pressure over heat-low region and Indian summer monsoon rainfall (ISMR) is also examined in this paper. During positive ESI tendency, heat-low temperature anomaly in February is significantly associated with ISMR, whereas during negative ESI tendency, both temperature/pressure over heat-low region in May are significantly associated with ISMR. These parameters may help in long range forecasting of ISMR.

Surface States of Microdroplet of Suspension

Surface thermodynamic states of single evaporating microdroplets of aqueous suspension of nanospheres were studied by analyzing the surface pressure (surface activity) isotherm. Surface pressure evolution was found from the temporal evolution of the droplet radius. The droplet radius was inferred from the azimuthal angular distribution of the irradiance of s-polarized scattered light. Several thermodynamic states of the surface layer formed of nanospheres were identified: surface gas, surface gas−liquid coexistence, two states of surface liquid, and surface solid. The collapse of the surface monolayer was detected.

Dynamics of penetration of dipalmitoyl-phosphatidyl-choline (DPPC) monolayers by β-casein

In this work we have analyzed the dynamics of the penetration of β-casein into dipalmitoyl-phosphatidyl-choline (DPPC) monolayers and the surface rheological characteristics (under dilatation and shear conditions) of mixed films formed by DPPC penetrated by β-casein. The penetration of β-casein into a DPPC monolayer was followed by measurements of the surface pressure ( π) increase at a constant surface area ( A) after the injection of β-casein into the aqueous phase, underneath the DPPC monolayer previously spread at the air–water interface, at different initial surface pressures ( π i) and at pH 5, 7, and 9. The evolution of surface pressure with time corresponds to an adsorption mechanism with three kinetic steps: (i) penetration of β-casein from underneath the DPPC monolayer, (ii) accumulation of the protein at the interface, and (iii) progressive penetration of β-casein into the DPPC monolayer. The results reflect the fact that β-casein–DPPC electrostatic interactions and the DPPC monolayer structure have an effect on the incorporation of β-casein into DPPC monolayers at the air–water interface. The penetration of β-casein is facilitated at acidic or neutral pH, but is hindered at basic pH. The surface viscoelastic properties under dilatational (using a ring trough with an isotropic area deformation) and shear (using an automatic Du Noüy ring oscillatory apparatus) conditions of a DPPC monolayer penetrated by β-casein are complementary and also demonstrated the complexity of the penetration mechanisms, due to the effect of electrostatic interactions between DPPC and β-casein as a function of the aqueous phase pH.

Objective synoptic classification combined with high resolution meteorological models for wind mesoscale studies

A methodology developed for automatic classification of Objective Synoptic Processes (OSP) and its application to the study of the mesoscale atmospheric circulatory patterns associated with them is described. The classification was based on the analysis of the evolution of surface pressure and geopotencial height at 500 hPa during three days. An iterative procedure results in an objective grouping of the main configurations describing different large-scale situations. This routine has been applied over an appropriate domain covering the Iberian Peninsula to obtain OSPs in the region for the two month period July–August, using daily synoptic maps for years 1990 to 1999 (a total of 7304 surface and 500 hPa synoptic maps have been used in the analysis). Finally, for a characteristic day for two of the OSPs obtained, a mesoscale meteorological model (TAPM) has been run at high resolution for the region of Catalonia, Northeastern Spain, in order to describe the local atmospheric circulatory patterns associated with a given large-scale situation. Results show that the complex orography modifies the large-scale forcings resulting in wind fields with a very important horizontal variability, significant daily cycle, and specific local features related to orographic elements, which the model was able to incorporate due to the highly-resolved orography used.

Equilibrium and dynamics of PEO/PPO/PEO penetration into DPPC monolayers

The interaction of synthetic polymers with living tissue is of interest in a wide range of biochemical and biomedical applications ranging from cell culture in large-scale bioreactors to pharmaceutic and cosmetic products. To gain insight into the physico-chemical interactions between polymeric material and cell membranes, we study the equilibrium and dynamic penetration of a symmetric triblock copolymer (PEO/PPO/PEO) into DPPC monolayers using a novel coaxial capillary pendant drop technique. A well-defined initial condition of the insoluble monolayer was established by first spreading the lipid onto a water drop formed at the tip of two (concentric) capillaries. The lipid was subsequently compressed to a specified surface state. Afterwards, the droplet subphase was exchanged by injecting a polymer solution from one of the capillaries and withdrawing liquid from the other under a constant total (drop) volume. The effects of polymer concentration and fractional coverage of the lipid monolayer on the surface pressure evolution were investigated. The data suggests that the adsorption of polymer into the lipid monolayer is reversible and that upon compression of the surface, the lipid can eject the macromolecule from the surface. A comparison of the equilibrium surface pressure of the penetrated monolayer with the surface pressure of the polymer alone shows that interactions in the adsorbed layer are non-ideal and consistent with polymer–lipid repulsion. Both desorption of the polymer from a suddenly compressed interface and response to oscillatory perturbation of the interface show that a characteristic timescale in the kinetics of monolayer relaxation is in the order of 100 s. Because of the elevated concentration of polymer in the bulk phase, this suggests a kinetic barrier to macromolecule adsorption/desorption.

Interfacial Behavior of Wheat Puroindolines: Study of Adsorption at the Air–Water Interface from Surface Tension Measurement Using Wilhelmy Plate Method

Adsorption of puroindolines (PIN-a and PIN-b), lipid binding proteins isolated from wheat endosperm at the air–water interface, was studied from the measurement of surface pressure using the Wilhelmy plate method under different physicochemical conditions like pH, ionic strength, and concentration of protein in the bulk medium. The adsorption process was highly cooperative and the initial step of adsorption was diffusion controlled. At relatively low concentrations, an induction time (ti) was observed in the time evolution of surface pressure for adsorption of PIN-a and PIN-b at the air–water interface. The induction time disappeared upon increasing the concentration of protein in the bulk medium. From the variation in surface pressure with time, the diffusion coefficients for the transfer of puroindolines from the bulk aqueous phase to the air–water interface were calculated from a modified form of the Ward and Tordai equation. The values of diffusion coefficients for PIN-a and PIN-b were found to be of the order of 10−6 cm2/s. Beyond diffusion, the adsorption was found to be nonlinear in nature indicating the existence of energy barriers in the adsorption process. The experimental data were analyzed using a first-order rate equation and it was observed that the adsorption took place involving a two-step process with which two distinct first-order rate constants (k1 and k2) were associated. In most cases, the values of k1 were higher than the values of k2. The adsorption process is dependent on the initial bulk concentration of the protein, the pH, and the ionic strength of the bulk medium. The presence of inorganic salts in the bulk medium had significant effects on the adsorption of PIN-a and PIN-b at the air–water interface. The experimental results obtained for PIN-a and PIN-b have been critically compared with each other and with previously obtained data for other globular proteins.

Flow Visualizations and Measurements of a Three-Dimensional Supersonic Separated Flow

The flow along the afterbody and in the base region of a circular cylinder with a length-to-radius ratio of 3.0 aligned at a 10-deg angle of attack to a nominal Mach 2.5 freestream has been investigated experimentally. The objective is to better understand the mechanisms that control base flow for supersonic bodies with a nonzero-angle-of-attack orientation. Laser Doppler velocimetry measurements were conducted in the incoming boundary layer to quantify the initial conditions at the onset of three-dimensional behavior. Schlieren and Mie scattering visualizations were obtained to discern governing flow features and to image the large-scale turbulent structures of this separated flow. Surface oil-streak visualizations were obtained to determine the three dimensionality of the afterbody surface flow and to deduce the base surface flowfield. Pressure-sensitive paint measurements were completed to determine the spatial evolution of surface pressure along the cylindrical body at angle of attack and to determine the change in base pressure caused by inclination of the body

Evidence that the Induction Time in the Surface Pressure Evolution of Lysozyme Solutions Is Caused by a Surface Phase Transition

Induction periods have been reported in the surface pressure evolution of a wide variety of proteins. In this work, this induction period is shown to be caused by a first-order phase change from a surface gaseous to a liquid-expanded state as the protein lysozyme adsorbs and decreases the mean area per molecule. The evolution of this transition is studied using concomitant fluorescence microscopy and surface pressure measurements. The fluorescent images are obtained by using spread films of the dye NBD-HDA at the air−liquid interface. This dye fluoresces when in contact with hydrophobic moieties and is quenched when in contact with water. The hydrophobic liquid-expanded domains therefore appear bright on a dark background. Lysozyme initially adsorbs to establish a surface gaseous phase, and the interface appears dark. The surface tension is fairly insensitive to changes in area per molecule in this state. Once the adsorbed concentration of lysozyme reaches the surface gaseous binodal, protein interactions drive a first-order phase change. Domains of liquid expanded phase grow at the interface at the expense of the surface gaseous phase. During this phase change, the surface tension remains constant. Only after the interface is covered in the bright, liquid-expanded phase does the surface tension decrease from the clean interface value. These results are discussed in terms of the surface coverage and orientation of lysozyme.

Study on the self-packing of SnO 2 nanoparticles at the air–hydrosol interface and its composite LB films with arachidic acid

SnO 2 nanoparticles were found to self-pack at the air–hydrosol interface and form a nanoparticulate film. The self-packed films were observed under a Brewster angle microscope, and investigated by recording the time evolution of surface pressure and π– A isotherms. The results show that SnO 2 nanoparticles take 3 h to form a complete film at the air–hydrosol interface. Composite monolayers of SnO 2 and arachidic acid were obtained by spreading arachidic acid onto a fresh hydrosol surface. Composite Y-type LB films were transferred from the air–hydrosol interface onto substrates, and characterized by FTIR, UV-vis, X-ray diffraction spectroscopy and TEM techniques. The results show that the composite films have good structure, with SnO 2 nanoparticles uniformly and compactly distributed in the arachidate matrix.

Enhanced Reactivity of the Epoxy Oligomers in Organized Monolayers at the Air-Water Interface

The behaviors of monolayers of novolac and diglycidyl ether of bisphenol A type epoxy oligomers on the surface of water were studied. Using a surface balance technique and FT-IR spectroscopy, it was found that the time evolution of surface pressure and surface area of the monolayers is controlled by the chemcial reactions of these oligomers with water and carbon dioxide. The specific reactivity of epoxy oligomers in a one-layer organized system at the air-water interface (in bulk similar reactions may proceed only under severe conditions) is enabled by the increased concentration and the mobility of protons in a thin layer of water adjacent to the monolayer and by the basicity of the epoxy groups of the oligomers. Surface reactions of epoxy oligomers are shown to be topochemical in nature ; the kinetics of these reactions may be described by the Avrami-Erofeev equation. The magnitudes of the parameters of this equation which were determined for the monolayers of each of the oligomers lead to the conclusion that, generally, the dynamics of epoxy oligomer monolayers is controlled by chemical transformations in and rearrangement of the surface layer.

Time-resolved observation of gas-dynamic discontinuities arising during excimer laser ablation and their interpretation

Ablation of materials (Cu is presented in this report) in air at an ambient gas pressure of 1 bar with a KrF excimer laser (3-47 J cm-2) leads to gasdynamic processes above the target surface which affect the processing result, the efficiency of the treatment and the debris in the environment of the irradiated area. These laser-induced processes have been diagnosed using fast schlieren photography and shadowgraphy. Five discontinuities have been discerned and their propagation mechanisms have been detected. A physical interpretation of the discontinuities is given along the lines of existing theories and plausible reasoning. The locally most advanced discontinuity can be explained by the classical Sedov-Taylor blast wave theory, and conclusions on the energy content in the shock wave, the pressure distribution and the surface pressure evolution will be presented. The results show that, at high energy densities (3-47 J cm-2), about 80% of the available laser pulse energy is deposited in the shock wave. A reduction in the energy density leads to a decrease in the fraction of the energy that is deposited in the shock wave. Close behind the first discontinuity follows a second one that is interpreted as the ionization front. The contact front, which separates shocked air and ablated material vapour, has been observed within the laser pulse duration. The complex structure of the contact front is interpreted in terms of gas flow phenomena inside the two outer discontinuities.

The Evolution of Surface Pressure and Temperature Measurement Techniques for Use in the Study of Lubrication in Metal Rolling

The paper describes the evolution of surface pressure and temperature transducers to a level of sophistication and reliability such that they can be used in the investigation of lubrication in sheet-rolling processes. The paper cites the development of these techniques from their inception (where they were used solely in the elastohydrodynamic regime) to their current application in the plastohydrodynamic and boundary lubrication regimes characteristic of sheet-rolling operations. The pressure and temperature data determined, using the transducers in experiments involving the rolling of steel sheet, show significant variation throughout the contact zone and these data are particularly influenced by changes in the lubricant and the deformation-process conditions.