Showing papers on "Pressure gradient published in 2020"

Effects of different shapes of nanoparticles on peristaltic flow of MHD nanofluids filled in an asymmetric channel

Abstract: An innovative approach to escalate the heat generation in peristalsis flow of MHD nanofluids filled in an asymmetric channel is proposed. Three different shapes of nanoparticles, namely (1) spherical, (2) disc and (3) cylindrical are utilized. Results for temperature, velocity and concentrations have been obtained analytically. The physical features for heat generation, concentration, pressure gradient, pressure rise and magnetic parameter have been elaborated graphically, whereas effects of Nusselt number and skin friction have been numerically computed by using the MATLAB software. For bolus features, trapping phenomena are also inspected by dint of stream lines. It is found that cylindrical shapes of nanoparticles have very low thermal conductivity as compared to spherical and disc shapes. Moreover, it is seen that the heat generation parameter always increases the temperature of nanofluid, and consequently, the trapping phenomena produce more boluses for larger values of heat source parameter.

Effect of adverse pressure gradients on turbulent wing boundary layers

Abstract: The characteristics of turbulent boundary layers (TBLs) subjected to adverse pressure gradients are analysed through well-resolved large-eddy simulations. The geometries under study are the NAC ...

Comparative study of hybrid nanofluids in microchannel slip flow induced by electroosmosis and peristalsis

Abstract: In this paper, a mathematical model is developed to investigate the electroosmotic flow of hybrid nanoliquids (containing dissimilar nanoparticles) through an asymmetric microchannel which moves sinusoidally with constant wave velocity under an axial electrical field. The effects of Joule heating are included. Maxwell and Brinkmann correlations are employed for nanoliquid thermal conductivity and viscosity. To study the performance of hybrid nanofluids, a selection of nanofluids is examined with water as the base fluid which is doped with titania, alumina or copper metallic nanoparticles. The boundary conditions include velocity slip and thermal slip at the microchannel walls. The Debye–Huckel linearization is employed. Numerical computations for velocity, pressure gradient and temperature fields are executed in the MATLAB bvp4c routine. The influence of selected physical parameters on the flow characteristics, pumping characteristics, and temperature distribution are computed. Pressure gradient is elevated with stronger buoyancy, i.e., higher thermal Grashof number and also electroosmosis parameter, whereas it is suppressed with greater velocity slip and thermal slip parameters. Axial flow is strongly accelerated with increasing Joule heating parameter and velocity slip. Periodic behavior is observed for axial pressure gradient for all three metallic nanoparticles due to the sinusoidal nature of the pumping. With increasing Brinkman number (dissipation parameter), the axial pressure gradient is decreased for alumina (Al2O3). The temperature is strongly increased with greater Joule heating parameter across the microchannel width for Cu–water nanoliquid. The temperature is increased for (Al2O3)–water nanofluid in the left microchannel half space with increasing thermal Grashof number, whereas it is decreased in the right half space. The temperatures are enhanced for titania (TiO2)–water nanoliquid in the left half space with greater velocity slip parameter, whereas they are diminished in the right half space. The present analysis is relevant to bio-inspired electrokinetic nanofluid micropump designs and emerging nanomedicine technologies.

Pore-scale dynamics and the multiphase Darcy law

Abstract: Time-resolved synchrotron x-ray microtomography combined with pressure measurements during two-phase displacement in porous media identifies three flow regimes. Intermittent occupancy creates temporary high-conductivity connections, leading to a power-law trend of pressure gradient with flow rate.

Heat transfer flow of Maxwell hybrid nanofluids due to pressure gradient into rectangular region.

Abstract: In this work, influence of hybrid nanofluids (Cu and $$\mathrm{Al}_{2}\mathrm{O}_{3}$$ ) on MHD Maxwell fluid due to pressure gradient are discussed. By introducing dimensionless variables the governing equations with all levied initial and boundary conditions are converted into dimensionless form. Fractional model for Maxwell fluid is established by Caputo time fractional differential operator. The dimensionless expression for concentration, temperature and velocity are found using Laplace transform. As a result, it is found that fluid properties show dual behavior for small and large time and by increasing volumetric fraction temperature increases and velocity decreases respectively. Further, we compared the Maxwell, Casson and Newtonian fluids and found that Newtonian fluid has greater velocity due to less viscosity. Draw the graphs of temperature and velocity by Mathcad software and discuss the behavior of flow parameters and the effect of fractional parameters.

Theoretical analysis of two-layered electro-osmotic peristaltic flow of FENE-P fluid in an axisymmetric tube

Abstract: This article presents the theoretical analysis of two-dimensional peristaltic transport of two-fluids in a flexible tube under the influence of electro-osmotic force. The flow domain is composed of two regions, namely, the core region and the peripheral region. The Newtonian and the FENE-P models are used to describe the rheology of fluids in the peripheral and the core regions, respectively. Governing flow equations corresponding to each region are developed under the assumption of long wavelength and low-Reynolds number. The interface between the two regions is computed numerically by employing a system of non-linear algebraic equations. The influence of relevant controlling parameters on pressure gradient, interface, trapping, and reflux is highlighted graphically and explained in detail. Special attention is given to estimate the effects of viscoelastic parameter of the core region fluid in the presence of electro-osmotic environment. Our investigation indicates an augmentation in the pressure loss at a zero volumetric flow rate with growing the viscoelastic and occlusion parameters. Moreover, trapping, reflux, and pumping efficiency are found to increase by increasing the electro-osmotic and viscoelastic parameters. The analysis presented here may be helpful in controlling the micro-vascular flow during the fractionation of blood into plasma (in the peripheral layer) and erythrocytes (core layer). This study may also have potential applications in areas such as electrophoresis, hematology, design, and improvement of bio-mimetic electro-osmotic pumps.

Fluid flow analysis of cilia beating in a curved channel in the presence of magnetic field and heat transfer

Abstract: This paper investigates fluid motion generated by cilia and a pressure gradient in a curved channel. The flow analysis is carried out in the presence of heat transfer and radial magnetic field. The...

Non-equilibrium three-dimensional boundary layers at moderate Reynolds numbers

Abstract: Non-equilibrium wall turbulence with mean-flow three-dimensionality is ubiquitous in geophysical and engineering flows. Under these conditions, turbulence may experience a counter-intuitive depletion of the turbulent stresses, which has important implications for modelling and control. Yet, current turbulence theories have been established mainly for statistically two-dimensional equilibrium flows and are unable to predict the reduction in the Reynolds stress magnitude. In the present work, we propose a multiscale model that captures the response of non-equilibrium wall-bounded turbulence under the imposition of three-dimensional strain. The analysis is performed via direct numerical simulation of transient three-dimensional turbulent channels subjected to a sudden lateral pressure gradient at friction Reynolds numbers up to 1000. We show that the flow regimes and scaling properties of the Reynolds stress are consistent with a model comprising momentum-carrying eddies with sizes and time scales proportional to their distance to the wall. We further demonstrate that the reduction in Reynolds stress follows a spatially and temporally self-similar evolution caused by the relative horizontal displacement between the core of the momentum-carrying eddies and the flow layer underneath. Inspection of the flow energetics reveals that this mechanism is associated with lower levels of pressure–strain correlation, which ultimately inhibits the generation of Reynolds stress, consistent with previous works. Finally, we assess the ability of the state-of-the-art wall-modelled large-eddy simulation to predict non-equilibrium three-dimensional flows.

Non-equilibrium development in turbulent boundary layers with changing pressure gradients

Abstract: Turbulence measurements were made in smooth-wall boundary layers subject to changing pressure gradients. Cases were documented over a range of Reynolds numbers and acceleration parameters. In all cases the boundary layer was subject to an initial zero pressure gradient (ZPG) development, followed by a favourable pressure gradient (FPG), a ZPG recovery and an adverse pressure gradient (APG). In the non-ZPG regions, the acceleration parameter, , was held constant. Two component velocity profiles were acquired at multiple streamwise locations to document the response to the changing pressure gradient of the mean velocity, Reynolds stresses and triple products of the fluctuating velocity components. Velocity field measurements were made to document the turbulence structure using two point correlations. In general, turbulence was suppressed by the FPG while structures became larger in streamwise and spanwise extent relative to the boundary layer thickness, particularly near the wall. In the recovery region, the return to canonical ZPG conditions was rapid. Changes in the structure in the APG region were less pronounced. The changes in the turbulence statistics and correlations relative to the ZPG baseline were quantified and presented as functions of streamwise location. When the streamwise location is scaled using the acceleration parameter, the results from all cases (including all statistical moments, and the size and inclination angles of turbulence structures), collapse in each region of the flow, showing a common non-equilibrium response to changes in the pressure gradient. These are new results which apply to the present flows and those with similar types of pressure gradients, but are not necessarily applicable to all flows with arbitrary pressure gradients.

Heat transfer analysis of peristaltic flow of a Phan-Thien–Tanner fluid model due to metachronal wave of cilia

Abstract: In the present investigation, we have studied the effects of heat transfer on the peristaltic flow considering the Phan-Thien-Tanner fluid model. The fluid is flowing in a uniform circular tube in the form of wave motion. The inner walls of the tube are considered to be ciliated with small hair-like structures. Exact solutions have been derived for velocity, temperature and pressure gradient. Mechanical properties of the fluid, such as velocity, temperature, pressure rise and pressure gradient, have been discussed graphically. Trapping phenomena due to the variation of physical parameters have been deliberated. It has been observed that when the viscous forces are greater than the elastic forces, the velocity of the fluid flow significantly decreases, thermal conductivity of the fluid improves and the pressure gradient along the tube increases.

Scrape-off layer (SOL) power width scaling and correlation between SOL and pedestal gradients across L, I and H-mode plasmas at ASDEX Upgrade

Abstract: A cross-regime (L-mode, I-mode and H-mode) database combining scrape-off layer (SOL) power decay length λq divertor measurements and upstream SOL electron pressure, temperature and density decay lengths has been assembled at ASDEX Upgrade. It is found that a cross-regime λq scaling is best described by a local edge quantity, such as the edge electron pressure evaluated at ρpol = 0.95. Furthermore, λq exhibits a clear correlation with edge electron pressure gradient lengths, no matter if taken inside or outside the separatrix. In addition, the database reveals that SOL and pedestal electron pressure gradients are remarkably well correlated across all confinement regimes. The physical interpretation of this observation is discussed with regard to an edge pressure critical gradient paradigm governing the edge physics and to a turbulence spreading in the SOL. Moreover, it is shown that the Spitzer–Harm electron conduction regime is a reasonable approximation to estimate λq across different confinement regimes. The main implication of these findings is that a widening of λq is linked to a reduction of edge electron pressure gradients.

Solving the Nonlinear Boundary Layer Flow Equations with Pressure Gradient and Radiation

Abstract: The physical problem under consideration is the boundary layer problem of an incompressible, laminar flow, taking place over a flat plate in the presence of a pressure gradient and radiation. For the mathematical formulation of the problem, the partial differential equations of continuity, energy, and momentum are taken into consideration with the boundary layer simplifications. Using the dimensionless Falkner–Skan transformation, a nonlinear, nonhomogeneous, coupled system of partial differential equations (PDEs) is obtained, which is solved via the homotopy analysis method. The obtained analytical solution describes radiation and pressure gradient effects on the boundary layer flow. These analytical results reveal that the adverse or favorable pressure gradient influences the dimensionless velocity and the dimensionless temperature of the boundary layer. An adverse pressure gradient causes significant changes on the dimensionless wall shear parameter and the dimensionless wall heat-transfer parameter. Thermal radiation influences the thermal boundary layer. The analytical results are in very good agreement with the corresponding numerical ones obtained using a modification of the Keller’s-box method.

The mechanisms behind perivascular fluid flow

Abstract: Flow of cerebrospinal fluid (CSF) in perivascular spaces (PVS) is one of the key concepts involved in theories concerning clearance from the brain Experimental studies have demonstrated both net and oscillatory movement of microspheres in PVS (Mestre et al (2018), Bedussi et al (2018)) The oscillatory particle movement has a clear cardiac component, while the mechanisms involved in net movement remain disputed Using computational fluid dynamics, we computed the CSF velocity and pressure in a PVS surrounding a cerebral artery subject to different forces, representing arterial wall expansion, systemic CSF pressure changes and rigid motions of the artery The arterial wall expansion generated velocity amplitudes of 60-260 {micro}m/s, which is in the upper range of previously observed values In the absence of a static pressure gradient, predicted net flow velocities were small (<05 {micro}m/s), though reaching up to 7 {micro}m/s for non-physiological PVS lengths In realistic geometries, a static systemic pressure increase of physiologically plausible magnitude was sufficient to induce net flow velocities of 20-30 {micro}m/s Moreover, rigid motions of the artery added to the complexity of flow patterns in the PVS Our study demonstrates that the combination of arterial wall expansion, rigid motions and a static CSF pressure gradient generates net and oscillatory PVS flow, quantitatively comparable with experimental findings The static CSF pressure gradient required for net flow is small, suggesting that its origin is yet to be determined Significance StatementCerebrospinal fluid flow along perivascular spaces is hypothesized to be instrumental for clearance of metabolic waste from the brain, such as eg clearance of amyloid-beta, a protein known to accumulate as plaque within the brain in Alzheimers patients Arterial pulsations have been proposed as the main driving mechanism for perivascular fluid flow, but it is unclear whether this mechanism alone is sufficient Our results show that arterial pulsations drive oscillatory movement in perivascular spaces, but also indicate that a pressure gradient is required for net flow However, the required pressure gradient is relatively small, thus suggesting that its origins can be associated with physiological processes within the brain and/or experimental procedures

Modeling Pore Pressure, Fracture Pressure and Collapse Pressure Gradients in Offshore Panna, Western India: Implications for Drilling and Wellbore Stability

Abstract: Pore pressure modeling has proven and direct implications in oil and gas exploration and development. Abnormal pore pressure leads to drilling complexity and well control issues because of reduced mud window, contributing to major non-productive times and steep drilling cost. A comprehensive pore pressure–fracture pressure model plays a critical role in successful well drilling. This work caters to the pressure modeling of Panna area in Mumbai offshore basin, western India. Two offshore wells, drilled through 4 km of Tertiary sedimentary succession down to Cretaceous basaltic basement, were analyzed to interpret the vertical stress, pore pressure, fracture gradient and collapse pressure. Vertical stress profile was generated from density logs; pore pressure was estimated using Eaton’s method by employing resistivity and sonic logs. Calculated pore pressure was calibrated with various direct downhole measurements and various well events. Compaction disequilibrium was inferred as key mechanism for generating mild overpressure in Oligocene to early Miocene shales (14–15 MPa/km), while it increases sharply against early Eocene sediments, and hard overpressure with near-lithostatic gradient (22 MPa/km) was detected in the underlying Paleocene shales. The mid-Eocene Bassein formation, the primary hydrocarbon reservoir, reveals sub-hydrostatic condition (7.5 MPa/km) resulting from production-related depletion. Estimated fracture pressure was calibrated with available leak-off test data. Mohr–Coulomb rock failure criterion was employed to estimate collapse pressure and validated with the observations from caliper log to address the wellbore stability issues. This study provides insights on downhole pressure behavior across stratigraphy, to achieve optimum drilling mud designing as well as safe and successful operational planning.