Surface Pressure Difference Research Articles

Are brain displacements and pressures within the parenchyma induced by surface pressure differences? A computational modelling study.

The intracranial pressure is implicated in many homeostatic processes in the brain and is a fundamental parameter in several diseases such as e.g. idiopathic normal pressure hydrocephalus. The presence of a small but persistent pulsatile intracranial pulsatile transmantle pressure gradient (on the order of a few mmHg/m at peak) has recently been demonstrated in hydrocephalus subjects. A key question is whether pulsatile intracranial pressure and displacements can be induced by a small pressure gradient originating from the brain surface alone. In this study, we model the brain parenchyma as either a linearly elastic or a poroelastic medium, and impose a pulsatile pressure gradient acting between the ventricular and the pial surfaces but no additional external forces. Using this high-resolution physics-based model, we use in vivo pulsatile pressure gradients from subjects with idiopathic normal pressure hydrocephalus to compute parenchyma displacement, volume change, fluid pressure, and fluid flux. The resulting displacement field is pulsatile and in qualitatively and quantitatively good agreement with the literature, both with elastic and poroelastic models. However, the pulsatile forces on the boundaries are not sufficient for pressure pulse propagation through the brain parenchyma. Our results suggest that pressure differences at the brain surface, originating e.g. from pulsating arteries surrounding the brain, are not alone sufficient to drive interstitial fluid flow within the brain parenchyma and that potential pressure gradients found within the parenchyma rather arise from a large portion of the blood vessel network, including smaller blood vessels within the brain parenchyma itself.

Numerical simulation of lateral jet interaction with rarefied hypersonic flow over a two-dimensional blunt body

Reaction Control System (RCS) is a direct force control system that successfully adjusts a craft's attitude or orbit using the reaction force created by jet flow. RCS is frequently employed in the management of near-space vehicles due to its properties of fast response time and effective control efficiency. When the near-space vehicle is navigating at high altitude in a low density atmosphere, the Navier–Stokes equation is no longer applicable. The numerical approach utilized in this study is known as the Conserved Discrete Unified Gas Kinetic Scheme, and the governing equation is the Boltzmann equation, which is not constrained by the continuum hypothesis. In velocity space, an unstructured mesh is utilized, which minimizes the amount of discrete velocity points and considerably increases computation efficiency. The numerical results are in good agreement with the direct simulation Monte Carlo code DS2V when modeling large Knudsen number lateral jet flow. The interaction flow field between hypersonic free stream and lateral jet is then simulated at altitudes of 60–90 km using argon as the working gas and a two-dimensional blunt cone with lateral jet as the study object. Under a fixed jet pressure ratio, preliminary research was conducted on the variation of the lateral jet interference flow field characteristics with the freestream Knudsen number and angle of attack. The differences in surface pressure and heat flux caused by jet opening and shutting are compared. Under rarefied atmospheric conditions, the variation of the force/moment amplification coefficient is given. The numerical results show that when the angle of attack is 0°, the separation area in front of the nozzle and a pair of opposite vortices, which are common in the jet interference flow field, gradually disappear with increasing altitude, but the separation vortex reappears when the angle of attack of the freestream is increased. The high-pressure region generated upstream of the nozzle is the primary cause of the extra force/moment. The density of the main flow decreases as altitude increases, various shock wave patterns of the interference flow field gradually dissipate and the force/moment amplification factor changes considerably. The rarefied gas effect has a significant effect on the lateral jet interference flow.

Investigation on aerodynamic noise for leading edge erosion of wind turbine blade

Wind turbine blade is extremely prone to leading edge erosion under complicated operation conditions. This decreases the aerodynamic performance and power generation efficiency of wind turbine. Currently acoustic-based erosion detection of the blade still faces a significant challenge. Consequently, this paper presents aerodynamic noise mechanism of the eroded blade using the computational fluid dynamics method. The Zonal Detached Delay Eddy Simulation turbulence model is applied to obtain the three-dimensional instantaneous turbulent flow field. Then the far-field aerodynamic noise is carried out using the Ffowcs Williams and Hawkings approach. Simulations are performed for the erosion condition that determined by the length and depth at leading edge of 5-MW National Renewable Laboratory wind turbine. Results indicate that erosion leads to unsteady pressure pulsation near the leading edge, decrease of surface pressure difference in tip area, increase of airflow separation region and forward movement of separation point. Furthermore, the eroded blade achieves higher acoustic level than that of the normal one. From the noise directivity of wind turbine blade, erosion causes obvious asymmetry of noise pattern in the upwind and downwind directions.

Interdecadal variations and causes of the relationship between the winter East Asian monsoon and interhemispheric atmospheric mass oscillation

The East Asian winter monsoon (EAWM) intensifies in the early twenty-first century and links with frequent impacts of large-scale persistent extreme cold events in winter in East Asia in recent years. We found that there has been a significant positive correlation between the EAWM and Interhemispheric Oscillation (IHO). However, conspicuous interdecadal variations have occurred in the relationship between the EAWM and IHO. The relationship between the IHO and EAWM was most significant during 1979–2020, but this relationship was weak and insignificant during 1962–1978. During 1979–2020, the atmospheric mass (surface pressure) difference between the Northern Hemisphere (NH) and Southern Hemisphere (SH) during 1979–2020 was significantly reduced by 7.85% (0.75 × 1015 kg) compared with that during 1962–1978. Such interhemispheric redistribution of atmospheric mass (AM) has had a distinct impact on the land-sea pressure contrast in East Asia and has intensified the connection between the EAWM and IHO. A strengthened EAWM has resulted in notable cooling and more severe winters in China. The apparent exportation of AM in the Antarctic region is an important driving factor for this interhemispheric change. The accompanying anomalous accumulation of AM in the NH is linked with an increase in the pressure difference between land and sea in East Asia, resulting in intensifying correlation between IHO and the EAWM. The decadal enhancement of the IHO during 1979–2020 was closely connected with conspicuous warming in the tropical troposphere/lower stratosphere (UTLS). A seesaw pattern of anomalous air temperature and ozone between tropical and Antarctic UTLS has induced a decrease in Antarctic ozone masses and air temperature and has strengthened the polar vortex, corresponding to a decadal enhancement of interhemispheric AM imbalance.

A Simulation Study of the Outdoor Wind Environment of Low Carbon Buildings in Cold Regions Based on PHOENICS Software

Based on PHOENICS software, the suitability of the outdoor wind environment at pedestrian heights of a low-carbon building under different operating conditions was quantitatively analysed using a κ-ε numerical model of low-speed turbulence. Three simulated conditions for the outdoor wind environment of low carbon buildings were determined by typical annual meteorological parameters for Shijiazhuang in cold regions. Combining the information on the full domain flow field obtained from the numerical simulations, the appropriate wind environment parameters were determined. The analysis of the wind environment indicators revealed that the low carbon buildings studied had clear year-round wind flow lines, with no dead zones and no obvious vortex areas. The wind speed at the pedestrian height of the low carbon building under different working conditions was less than 5 m/s (Wind speed in winter, summer and transitional season were 2.95 m/s, 2.54 m/s, and 3.3 m/s respectively), which meets the requirements of human comfort and standard regulations. The surface pressure difference between the different operating conditions (winter, summer and transitional seasons) of the low carbon building is not higher than 5 Pa, which meets the requirements for wind protection in winter in the area and contributes to the comfort level required for ventilation in summer. The study of the building wind environment can effectively identify the gap between the design and the actual use process, providing effective reference and guidance for the actual construction.

Study on treatment of wastewater with low concentration of ammonia-nitrogen by vacuum plate membrane distillation technology.

The removal of low concentration ammonia-nitrogen in industrial wastewater is necessary before discharged into the environment. In this study, vacuum plate membrane distillation (VPMD) technology was utilized and operating parameters such as pH, feed temperature, vacuum degree, feed flow and time were investigated. Based on the experimental data, the heat and mass transfer mechanism and mathematic model were studied. The experimental results show that low solution pH was significantly beneficial to ammonia-nitrogen removal but permeate flux was nearly changeless. At pH = 4, a removal rate up to 93.33% was achieved. Ammonia-nitrogen mainly exists with NH4+ ions in acidic solution, so only water molecules pass through the membrane to acquire the water product in the permeate side. Increasing the temperature of the solution was disadvantageous to the ammonia-nitrogen removal due to membrane pores expanding and the mass transfer coefficient of NH3 molecules increasing; therefore a low temperature was chosen if possible. Because vapor pressure of the feed solution increases exponentially with temperature and results in membrane surface pressure difference increases, therefore increasing the temperature enhances the permeate flux. Raising the vacuum degree enhanced ammonia removal rate and permeate flux obviously, a vacuum degree of 0.09 MPa was chosen for the experiment. The effect of feed flow rate on ammonia-nitrogen removal instead of permeate flux is weak, the reason is that the boundary layer wears thin when the feed flow rate is increased, which is conducive to permeate flux increasing. In a two-parameter model of Knudsen diffusion, Poiseuille flow was chosen to demonstrate the heat and mass transfers in the process of VPMD in the study. Based on the experimental values of permeate flux, two parameters CK and CP in the model were calculated using a nonlinear fitting method software, which indicated that the Knudsen diffusion model more than the Poiseuille flow model was suitable. The maximum values of the relative average deviation (RAD) and root mean square difference (RMSD) of experimental and calculated values with model equations of the permeate flux at the different temperature, vacuum degree and feed flow rate were no more than 8.7% and 3.20 kg · (m2 · h)-1, respectively.

A Fresh Look at the Young-Laplace Equation and Its Many Applications in Hydrostatics

The Young-Laplace (Y-L) equation relates the pressure difference across the interface of two fluids (such as air and water) to the curvature of the interface. The pressure rises on crossing a convex interface such as a rain drop and falls on crossing a concave interface such as the meniscus of water in a glass capillary. The relation between surface geometry and pressure difference across the interface provides the key concept in understanding a large collection of phenomena in hydrostatics. Of the many phenomena in hydrostatics that can be explained readily by the application of the Y-L equation, we consider the ones that are of particular interest in the introductory physics courses. These include the differential pressure within soap bubbles and liquid droplets, the rise and fall of liquids in capillaries, and the depth of liquid spills.

Extension of Spectral/hp Element Methods towards Robust Large-Eddy Simulation of Industrial Automotive Geometries

A spectral/hp element methodology is utilised to investigate the SAE Notchback geometry with 20∘ backlight and 3∘ diffuser at Re=2.3×106. The study presented here considered two different mesh approaches: one focusing on classical h-type refinement with standard solution polynomial order (HFP3) and a second case considering relatively coarse mesh combined with high solution polynomial order (HCP5). For the same targeted number of degrees of freedom in both meshes, the results show significant differences in vorticity, flow structures and surface pressure. The first guidelines for hp refinement strategy are deduced for complex industrial cases. Further work on investigating the requirements for these hybrid techniques is required in order to maximize the benefits of the solution and mesh refinements in spectral/hp element method simulations.

Analytic approximation for the collapse of viscous tubes driven by surface tension and pressure difference

In this work, an approximate analytic formula is developed which accurately models the one-dimensional collapse kinetics of viscous glass tubes, driven by surface tension and low-to-moderate pressure differences. This is in contrast to existing analytic approaches from the literature where either surface tension is the only driving force, or extremely high pressure differences are assumed. Extensive model validation is provided against numerical computation of the exact one-dimensional and two-dimensional models for cross-sectional collapse, as well as with experimental data from the literature. Practical utility of this formula is demonstrated for effortlessly solving the inverse problem for determining the viscosity and surface tension of glass tubes.

Noise reduction of bionic coupling blades of horizontal axis wind turbine

Many bio-inspired researches for aerodynamic noise control of wind turbine have been carried out and obtained effective results. Inspired by the silent flight of owl, in this paper, the airfoil of owl's wing and the asymmetric sawtooth structure of the feather have been extracted and reconstructed on the prototype wind turbine blades. The bionic airfoil blade and bionic coupling blade have been designed separately and compared with prototype blade. To obtain the asymmetric sawtooth structure with better acoustic performance, the sawtooth parameters are selected by orthogonal test. The influence of airfoil and asymmetric sawtooth for acoustic performance of blade has been investigated with large eddy simulation method and Ffowcs Williams-Hawkings analogy method. The results show that the bionic coupling blade has a larger surface pressure difference compared with the prototype blade and thus has better aerodynamic performance. The airfoil-structure coupling method can effectively reduce the aerodynamic noise of the blade without affecting the directivity of the acoustic, and optimized blade can reduce the noise by up to 8.42 dB. The blade coupling airfoil has an inhibitory effect on intermediate and high frequency noise. After adding asymmetric sawtooth trailing edge, the noise in the low frequency and intermediate frequency range is further reduced.

Influence of suction flow control on energy extraction characteristics of flapping foil

ABSTRACT Flapping foil (FF) is a relatively new renewable energy extraction device, which has the advantages of simple structure, strong environmental adaptability and little impact on the environment. This study proposed a new FF energy extraction equipment with suction control added to the surface. Based on the moving grid technology, the effect of different suction control methods on energy extraction characteristics of FF was numerically investigated. In this paper, taking NACA0012 as the reference airfoil, the influence laws of key parameters, such as suction velocity, suction port position and suction mode on the energy extraction efficiency of FF were studied respectively. The results show that, compared with the original FF, the addition of suction control can effectively control the size of the leading edge negative effect vortex, increase the force consistent with the motion direction of the FF and its surface pressure difference, thus improving the energy extraction efficiency. In addition, the innovative change of suction mode to sinusoidal suction mode in this paper can not only enhance the stability and safety of FF operation structure, but also its energy extraction efficiency is not much different from that of FF with sudden suction control.

Ensemble Kalman filter for vortex models of disturbed aerodynamic flows

The task of dynamic flow estimation is to construct an approximation of an evolving flow---and particularly, its response to disturbances---using measurements from available sensors. Building from previous work by Darakananda et al.~(Phys Rev Fluids 2018), we further develop an ensemble Kalman filter (EnKF) framework for aerodynamic flows based on an ensemble of randomly-perturbed inviscid vortex models of flow about an infinitely-thin plate. In the forecast step, vortex elements in each ensemble member are advected by the flow and new elements are released from each edge of the plate; the elements are aggregated to maintain an efficient representation. The vortex elements and leading edge constraint are corrected in the analysis step by assimilating the surface pressure differences across the plate measured from the truth system. We show that the overall framework can be physically interpreted as a series of adjustments to the position and shape of an elliptical region of uncertainty associated with each vortex element. In this work, we compare the previously-used stochastic EnKF with the ensemble transform Kalman filter (ETKF), which uses a deterministic analysis step. We examine the response of the flat plate at $20^\circ$ in two perturbed flows, with truth data obtained from high-fidelity simulation at Reynolds number 500. In the first case, we apply a sequence of large-amplitude pulses near the leading edge of the plate to mimic flow actuation. In the second, we place the plate in a vortex street wake behind a cylinder. In both cases, we show that the vortex-based framework accurately estimates the pressure distribution and normal force, with no {\em a priori} knowledge of the perturbations. We show that the ETKF is consistently more robust than the stochastic EnKF. Finally, we examine the mapping from measurements to state update in the analysis step through SVD of the Kalman gain.

On the noise reduction of a porous trailing edge applied to an airfoil at lifting condition

Numerical simulations, using a lattice-Boltzmann technique, have been carried out to study the effect of aerodynamic loading and Reynolds number on the aeroacoustics of a porous trailing-edge insert. The airfoil is a National Advisory Committee for Aeronautics 0018 with the last 20% of its chord being replaceable with porous insert based on a Ni-Cr-Al metal foam with a mean pore diameter of 0.8 mm. The porous insert is modeled as an equivalent fluid region governed by the Darcy's law. The angle-of-attack is set to 7.8°, and the freestream Reynolds numbers based on the airfoil chord are 2.7 × 105 and 5.4 × 105. The amount of noise reduction produced by the porous insert generally decreases as the angle-of-attack or Reynolds number is increased, although the far-field noise directivity remains similar to that of the solid insert case. Unlike for a solid insert, in which noise sources are concentrated at the trailing edge, those on the porous insert are distributed across the porous medium surface, and they promote phase interference effect that causes noise attenuation. This mechanism is realized by the pressure release process, which refers to the interaction between surface pressure fluctuations on both sides of the trailing edge through the porous medium. It is found that the pressure release process is strongly present at the last 25% of the porous insert extent, and thus the upstream segment plays a relatively limited role in noise attenuation. The porous insert also causes velocity deficit, enhanced Reynolds shear stress, and lower convection velocity in the turbulent boundary layer. Nevertheless, since only the flow field surrounding the porous insert is affected, the overall aerodynamic penalty is relatively minor. It has also been found that the effect of mean cross-flow inside the porous medium is almost negligible in the present investigation due to the small surface pressure difference between the two sides of the porous insert.

Irreversibility analysis in Marangoni forced convection flow of second grade fluid

Marangoni forced convective MHD flow of second grade liquid is scrutinized. Heat source/sink, Joule heating and dissipation are addressed in energy equation. Physical aspects of entropy optimization with binary chemical reaction are addressed. Energy and entropy expressions are computed. Marangoni convection influenced on the surface pressure difference is calculated through temperature gradient, magnetic field and concentration gradient. Nonlinear PDE’s are reduced to ordinary one through suitable variables. Nonlinear system is computed for convergent solution by employing of OHAM. Characteristics of different influential parameters on entropy generation, concentration, temperature, Bejan number and velocity are graphically deliberated. Velocity enhances via Marangoni ratio parameter. Velocity and temperature have reverse effects for higher approximation of magnetic variable. For higher second grade fluid parameter the velocity is augmented. An increment occurs in temperature against higher values of Brinkman number and fluid parameter. Concentration decrease versus higher Marangoni ratio parameter. Entropy optimization upsurges for rising values of fluid parameters. Some relevant applications of Marangoni convection effect include atomic reactor, semiconductor processing, thin-film stretching, silicon wafers, soap films, material sciences, nanotechnology and applied physics etc. Entropy supports to progress the importance of numerous engineering and electronic devices development.

Characterization of Marangoni Forced Convection in Casson Nanoliquid Flow with Joule Heating and Irreversibility.

The Marangoni forced convective inclined magnetohydrodynamic flow is examined. Marangoni forced convection depends on the differences in surface pressure computed by magnetic field, temperature, and concentration gradient. Casson nanoliquid flow by an infinite disk is considered. Viscous dissipation, heat flux, and Joule heating are addressed in energy expressions. Thermophoresis and Brownian motion are also examined. Entropy generation is computed. The physical characteristics of entropy optimization with Arrhenius activation energy are discussed. Nonlinear PDE’s are reduced to highly nonlinear ordinary systems with appropriate transformations. A nonlinear system is numerically computed by the NDSolve technique. The salient characteristics of velocity, temperature, concentration, entropy generation, and Bejan number are explained. The computational results of the heat-transfer rate and concentration gradient are examined through tables. Velocity and temperature have reverse effects for the higher approximation of the Marangoni number. Velocity is a decreasing function of the Casson fluid parameter. Temperature is enhanced for higher radiation during reverse hold for concentration against the Marangoni number. The Bejan number and entropy generation have similar effects for Casson fluid and radiation parameters. For a higher estimation of the Brinkman number, the entropy optimization is augmented.

Numerical Analysis of Leading-Edge Vortex Effect on Tidal Current Energy Extraction Performance for Chord-Wise Deformable Oscillating Hydrofoil

To improve the energy extraction performance of the oscillating hydrofoil, the lift force that acts on the oscillating hydrofoil is analyzed. The pressure difference between the oscillating hydrofoil‘s opposing surfaces is dominant to generate the lift force. Forming and shedding of the leading-edge vortex from the hydrofoil surface determines the pressure difference between the opposing surfaces of the oscillating hydrofoil. In this paper, the hydrofoil with different chord flexibility coefficients and maximum offset at the trailing edge are analyzed to obtain the power coefficient, lift coefficient, and moment coefficient of the oscillating hydrofoil. The influence mechanism of chord-wise deformation of the oscillating hydrofoil on the energy extraction performance is explored. According to the Kutta–Joukowsky condition and the Stokes’ theorem, the relationship between the attached vortex on the hydrofoil and the surface pressure of the hydrofoil, the surface pressure difference of the hydrofoil, and the lift force that acts on the hydrofoil are investigated. By quantifying the vortex intensity, the ascending-shedding process of the attached vortex on the hydrofoil is characterized. Finally, the complete influence chain among the chord-wise flexure, the attached vortex on the hydrofoil, and the energy extraction performance of the oscillating hydrofoil is established.

Dynamics of bubble formation in highly viscous liquid in co-flowing microfluidic device

In this work, the dynamics of bubble formation in a highly viscous liquid in a co-flowing microfluidic device is experimentally investigated. The evolution of gaseous thread in the co-flowing device is recorded using a high-speed camera. The bubble formation process can be divided into three stages: retraction stage, expansion stage, and collapse stage. According to an analysis of the forces acting on the gaseous thread, the bubble formation in the co-flowing device is a competitive result of the surface tension, pressure difference and shearing effects. The surface tension effect plays an important role in the retraction stage. In the expansion stage, the pressure difference effect dominates the bubble’s growth. While in the collapse stage, the shearing effect leads to the interface breakup. Three empirical correlations are proposed according to the experimental data and can be used to predict bubble formation frequency, the diameter and length of the generated bubbles.

Growth rate and oscillation frequency of electrified jet and droplet: Effects of charge and electric field

AbstractElectrified jets are applied industrially in agriculture, automobiles, targeted drug delivery systems, spacecraft propulsion units, liquid metal sprayers, ion sources, emulsifiers, dust scavenging systems, and ink-jet printers. Electrified columnar jets experience instability caused by electrohydrodynamic interactions of the charged liquid surfaces with electric fields. Electrostatic and surface tension forces competing along the liquid surface create surface pressure differences. The temporal rise and fall of the surface pressure induce oscillations of jets and droplet. A linear theory was derived to yield a dispersion equation determining the most dominant wavelength of oscillation for a given charge level and electric field; this enabled the estimation of the diameter of an atomized droplet. In addition, the frequency of oscillation was derived for a cylindrical jet and spherical droplet. Parametric studies were performed for various charging levels and electric field strengths.© 2018 American ...

Effects of Tip Vanes on Aerodynamic Performance of H-Type VAWT

In order to investigate the effect of the tip vanes on the aerodynamic performance of H-type vertical axis wind turbines (H-VAWTs), adopting the method of the CFD numerical simulation to analysis blade surface pressure distribution, tip vortex and power coefficient of H-VAWTs that are installed two different kinds of tip vanes on both ends of the blade and not installed. The result showed that the tip vanes can weaken the tip vortex, increase the blade surface pressure difference and improve the power coefficient of the H-VAWT. In addition, the power coefficient of the rotor with V type tip vane was greater than that of the rotor with S type tip vane. The maximum improvement achieved was a 37.5 percent increase in power coefficient with V type tip vane and a 33 percent increase in power coefficient with S type tip vane, the tip vanes made the power augmentation of the H-VAWT.

Self-Growing and Serpentine Locomotion of Liquid Metal Induced by Copper Ions.

The realization of serpentine locomotion has been a core goal pursued. Here, a straightforward approach was discovered to generate the serpentine locomotion based on a brand-new phenomenon observed on liquid metal (Ga67In21Sn12). The dynamic process that liquid metal can automatically produce and move like tremendous slim snakes was revealed and the underlying mechanisms were clarified and interpreted. It was found that the self-growing serpentine locomotion of liquid metal is driven by the localized surface pressure difference related to the unbalanced surface tension. The present work offers new insight and forms in developing future autonomous soft systems and bionic multifunctional robots.