Flow Velocity Profiles Research Articles

Dynamics of coronary artery velocity flow during exercise echocardiography

Purpose The aim of our study was to acquire non-invasive data from coronary flow velocity profiles during exercise in groups of healthy subjects and of patients with arterial hypertension. Material and Methods We enrolled 83 patients into two groups: (1) 35 non-selected consecutive healthy subjects; (2) 25 consecutive patients with arterial hypertension. All the patients performed supine bicycle symptoms-limited tests. Throughout exercise the diastolic peaks of coronary flow velocity in LAD were recorded. Coronary flow velocity reserve (CFVR) was calculated off-line. Profiles of coronary artery velocity were acquired for all groups. The coronary artery flow parameters investigated were comparable in healthy and hypertensive patients at every stage. Results The average diastolic velocities were 54.8 ± 12.9 vs. 51.8 ± 12.2 cm/s, at 50 W; 69.2 ± 17.1 vs 64.4 ± 19.1 cm/s at 75 W; 70.7 ± 16.4 vs. 76.1 ± 19.0 cm/s at 100 W; 80.0 ± 16.0 vs. 72.9 ± 16.1 cm/s at 125 W; 83.7 ± 12.2 vs. 81.4 ± 17.0 at 150 W, p- non-significant, respectively. On average, the healthy group reached CFVR > 2.0 at a heart rate of 110–120 beats/min at 75 W. During supine bicycle exercise, healthy subjects and patients with arterial hypertension have a similar coronary artery flow velocity profile. Conclusion The routine exercise echocardiography test can feasibly be supplemented with the additional measurement of coronary flow velocity during routine supine exercise stress tests, as the normal range of CFVR is reached before submaximal heart rate.

Impact of off-bottom seaweed cultivation on turbulent variation in the hydrodynamic environment: A flume experiment study with mimic and natural Saccharina latissima thalli

The seaweed industry is growing worldwide to meet future resource needs in terms of food and fuel. In the meantime, the impact of expanding off-bottom seaweed cultivation on its environment is unclear. For example, it remains poorly understood how off-bottom seaweeds affect the local hydrodynamic environment, especially concerning turbulence that is more important for nutrient transport and availability than the mean flow velocity. Here, we carried out well-controlled flume experiments with mimic seaweed thalli, which are available, controllable, and stable, to investigate the impact of off-bottom seaweed canopies on whole-depth flow velocities in terms of both mean flow and turbulence velocity profiles. A careful comparison of behavior in the flow between natural and mimic seaweed thalli was made before these experiments. The results show that the floating seaweed thalli generate a surface boundary layer and have a profound impact on the velocity structure in the bottom boundary layer. More importantly, the generation, growth and dissipation of turbulence in the seaweed thalli area deeply affect the downstream distribution of near-bed turbulent strength and associated bed shear stress. Ignoring this turbulent variation would cause inaccurate predictions of morphological changes of the seabed. Our findings suggest that expanding the seaweed cultivation area may cause high risks of bed degradation and low diffusion in the downstream cultivation area. These findings provide novel insights into the environmental influence of off-bottom seaweed cultivation, with important implications for optimizing management strategies to promote seaweed productivity while minimizing seabed destabilization.

Measurement of granular temperature and velocity profile of granular flow in silos

In this paper we report experimental results on the granular temperature and velocity profile of glass beads in steady-state flow inside a flat-bottomed silo. We found that the dynamics of the granular system during the discharge is stable on the mesoscopic scale. In particular, the ordered directional movement of particles can occur near the orifice. In addition, the correlation between the granular temperature distribution and velocity vector field is opposite in the radial and axial directions. According to the kinetic model, the main cause for the reversal of spatial correlation is that the intensity of the particle diffusion decrease with the decrease of silo height. This highlights a surprising and unrecognized role that the diffusion motion of particles plays in energy dissipation for hopper flow.

INFLUENCE OF WATER HYACINTH UNIFORM DISTRIBUTION ON VERTICAL VELOCITY PROFILE AND DRAG COEFFICIENT IN IRRIGATION CANALS

The presence of aquatic vegetation in irrigation canals retards water flow through additional drag force. The aim of this study is to present the impact of water hyacinth on flow velocity profile and drag coefficient in irrigation canals. To achieve this aim experimental program was carried out in a circulating water flume, using water hyacinth. Four different vegetation densities, three different vegetation root depths and three different vegetation zone lengths were used with smooth and rough channel bed. The case without water hyacinth was considered as comparative case. It was found that, for the case without water hyacinth, vertical velocity profile was resembled for theoretical logarithmic distribution in open channel. For the case with water hyacinth velocity vertical profiles became close to the theoretical velocity distribution in a closed conduit but did not reach zero at water surface. Also vegetation density, vegetation root depth, vegetation zone length and bed roughness have a significant effect on the position of maximum velocity. Also the vegetation drag force increases by increasing vegetation density, vegetation root depth and vegetation zone length. In addition, equations were deduced using multiple linear regression analysis to calculate vegetation drag force for both smooth and rough flume bed.

Unsteady boundary layer flow of Williamson nanofluids over a heated permeable stretching sheet embedded in porous medium in the presence of viscous dissipation

The main objective of this paper is to focus on a numerical study of unsteady boundary layer flow of Williamson Nanofluids over a heated permeable stretching sheet embedded in porous medium in the presence of viscous dissipation. A mathematical modeled which resembles the physical flow problem has been developed. By using an appropriate transformation, we converted the system of dimensional nonlinear partial differential equations into system of coupled dimensionless ordinary differential equations. Numerical solutions of these equations are obtained by Runge-Kutta fourth order with shooting method. The velocity, temperature and concentration distributions are discussed numerically and presented through graphs. The numerical values of reduced skin-friction coefficient, Nusselt number and Sherwood number at the plate are derived and discussed numerically for various values of physical parameters which are presented through tables. The present results have been compared with existing one for some limiting case and found excellent validation. It is analyzed that the reduced skin friction coefficient enhances with increasing values of an unsteady parameter, magnetic parameter and porosity parameter. In addition, we observe that decrement in velocity profile of the fluid flow is observed for increasing values of the non-Newtonian Williamson parameter and a rise in Eckert number leads to the enhancement of the temperature of the fluid in the thermal boundary layer.

Simulation of flow past a sphere on a rough bed using smoothed particle hydrodynamics (SPH)

This paper presents an investigation of flow past a sphere on a rough surface by means of simulation using the meshless numerical method, smoothed particle hydrodynamics (SPH) in the presence of a free surface. A representative of natural and engineered objects is spherical wall-mounted bodies. These are ideal to study the flow conditions around hydraulic structures, boulders, fish habitat structures or even architectural structures. The aim is to understand their effect on the hydrodynamics around the larger object sphere resting on them and their interaction. The Lagrangian particle-based scheme SPH using the open-source code DualSPHysics is validated against datasets from a laboratory-based flume experiment. The validation case was selected from the family of the flow past a sphere test cases since it reproduces the flow features in a simplified manner that can be observed in the vicinity of natural sediment grains or larger bodies. The validation results include flow velocity profiles in the vicinity of the large sphere and comparison with experiment data. The results stand in overall agreement with the experimental velocity and force measurements that demonstrates the applicability of SPH in aquatic environments. An SPH investigation on a rough bed in combination with objects/body near the bed in the presence of a free-surface flow has not been shown before in the literature. This is a novel application with insight into the fluid mechanics made possible by using DualSPHysics solver.

Effect of Compressibility on Velocity Profile and Friction Factor of Gaseous Laminar Flows in a Microtube

Abstract Laminar flow of nitrogen gas in a microtube was simulated numerically to obtain velocity profile and Fanning friction factor in a quasi-fully developed region. The numerical procedure based on Arbitrary-Lagrangian-Eulerian method solved two-dimensional compressible momentum and energy equations. The computations were performed for a wide range of Reynolds number in laminar flow regime with adiabatic wall condition. It was found that the velocity profile deviates from the parabola as Mach number increases, and the product of Fanning friction factor and Reynolds number is not a constant but a function of only Mach number. To explain the compressibility effect, a new theoretical flow model which gives the velocity profile of gaseous laminar flows in a microtube was proposed under the assumption of purely axial flow. The theoretical velocity profile is taking radial-direction density change into account, and coincides with the numerically obtained velocity profile. The proposed flow model also shows that the Fanning friction factor of a compressible flow in a microtube is expressed by a quadratic function of Mach number. The coefficient of the Mach squared term is 40% of the numerically obtained correlation. The compressibility effect on friction factor of gaseous laminar flows in a microtube partly results from velocity profile change which must occur to keep the mass velocity profile when density changes in radial direction. The remainder of the compressibility effect can be considered to result from actual mass transfer in the radial direction whose existence was demonstrated by the numerical results.

Analysis of Hiemenz flow of Reiner-Rivlin fluid over a stretching/shrinking sheet

PurposeThis paper aims to theoretically and numerically investigate the steady two-dimensional (2D) Hiemenz flow with heat transfer of Reiner-Rivlin fluid over a linearly stretching/shrinking sheet.Design/methodology/approachThe Navier–Stokes equations are transformed into self-similar equations using appropriate similarity transformations and then solved numerically by using shooting technique. A simple but effective mathematical analysis has been used to prove the existence of a solution for stretching case (λ> 0). Moreover, an attempt has been laid to carry the asymptotic solution behavior for large stretching. The obtained asymptotic solutions are compared with direct numerical solutions, and the comparison is quite remarkable.FindingsIt is observed that the self-similar equations exhibit dual solutions within the range [λc, −1] of shrinking parameter λ, where λc is the turning point from where the dual solutions bifurcate. Unique solution is found for all stretching case (λ > 0). It is noticed that the effects of cross-viscous parameter L and shrinking parameter λ on velocity and thermal fields show opposite character in the dual solution branches. Thus, a linear temporal stability analysis is performed to determine the basic feasible solution. The stability analysis is based on the sign of the smallest eigenvalue, where positive or negative sign leading to a stable or unstable solution. The stability analysis reveals that the first solution is stable that describes the main flow. Increase in cross-viscous parameter L resulting in a significant increment in skin friction coefficient, local Nusselt number and dual solutions domain.Originality/valueThis work’s originality is to examine the combined effects of cross-viscous parameter and stretching/shrinking parameter on skin friction coefficient, local Nusselt number, velocity and temperature profiles of Hiemenz flow over a stretching/shrinking sheet. Although many studies on viscous fluid and nanofluid have been investigated in this field, there are still limited discoveries on non-Newtonian fluids. The obtained results can be used as a benchmark for future studies of higher-grade non-Newtonian flows with several physical aspects. All the generated results are claimed to be novel and have not been published elsewhere.

Shifted Legendre Collocation Method for the Solution of Unsteady Viscous-Ohmic Dissipative Hybrid Ferrofluid Flow over a Cylinder.

A numerical treatment for the unsteady viscous-Ohmic dissipative flow of hybrid ferrofluid over a contracting cylinder is provided in this study. The hybrid ferrofluid was prepared by mixing a 50% water (HO) + 50% ethylene glycol base fluid with a hybrid combination of magnetite (FeO and cobalt ferrite (CoFeO ferroparticles. Suitable parameters were considered for the conversion of partial differential equations (PDEs) into ordinary differential equations (ODEs). The numerical solutions were established by expanding the unknowns and employing the truncated series of shifted Legendre polynomials. We begin by collocating the transformed ODEs by setting the collocation points. These collocated equations yield a system of algebraic equations containing shifted Legendre coefficients, which can be obtained by solving this system of equations. The effect of the various influencing parameters on the velocity and temperature flow profiles were plotted graphically and discussed in detail. The effects of the parameters on the skin friction coefficient and heat transfer rates were further presented. From the discussion, we come to the understanding that Eckert number considerably decreases both the skin friction coefficient and the heat transfer rate.

Counterflow slip in a two-fluid whirlpool

This experimental study reveals a counterflow slip at the interface of two immiscible fluids filling a sealed vertical cylindrical container whose bottom disk rotates while other walls are stationary. An advanced particle image velocimetry helps us analyze and quantify streamline patterns and velocity profiles of the steady axisymmetric flows of both fluids. As the angular velocity of a disk increases, starting from zero, three changes occur in topology of the upper-fluid flow while topology of the lower-fluid flow remains invariant. These changes result in the counterflow slip at the entire interface, whose nature is speculatively discussed and requires further research.

Oblique stationary solitary waves in turbulent free-surface flow

It is shown that an oblique solitary wave may be caused by an oblique strip of enlarged bottom roughness. The analysis is valid for very large Reynolds numbers and very small slopes. Considered are strips with a constant width in the longitudinal direction and with constant roughness. For a strip whose length is much larger than its width, the equations of motion can be simplified by assuming a three-dimensional flow that is independent of the coordinate in the longitudinal direction of the strip. Furthermore, it is assumed that the Froude number in terms of the velocity component normal to the strip is slightly larger than the critical value 1. This facilitates application of an asymptotic expansion method developed previously for plane flow. The analysis does not require modeling of the Reynolds stresses. It turns out that the velocity profile of the three-dimensional flow is not skewed in the first order. The shape, amplitude, and position of the oblique stationary wave are obtained from solutions of the steady-state version of an extended Korteweg-de-Vries equation. In general, the oblique wave is a classical solitary wave with a long, but shallow tail. However, tails are missing for certain combinations of Froude number and parameters characterizing the strip. Measurements and numerical solutions of the full Reynolds equations are already available for orthogonal solitary waves, lending support to the results of the asymptotic analysis. In addition, a novel boundary condition at the free surface is given, and the velocity distribution in fully developed flow is determined.

Acoustic Metagrating Circulators: Nonreciprocal, Robust, and Tunable Manipulation with Unitary Efficiency

Nonreciprocal signal operation is highly desired for various acoustic applications, where protection from unwanted backscattering can be realized so that transmitting and receiving signals are processed in a full-duplex mode. Here we present the realization of a class of nonreciprocal circulators based on simply structured acoustic metagratings, which consist only of a few solid cylinders and a steady fluid flow with low velocity. These innovative metagratings are intelligently designed via a diffraction analysis of the linearized potential flow equation and a genetic-algorithm-based optimization process. Unitary reflection efficiency between desired ports of the circulators are demonstrated through full-wave numerical simulations, confirming nonreciprocal and robust circulation of the acoustic signal over a broad range of flow velocity magnitude and profile. Our design provides a feasible degree of tunability, including switching from reciprocal to nonreciprocal operation and reversing the handedness of the circulator, presenting a convenient but efficient approach for the realization of nonreciprocal acoustic devices from wavelength-thick metagratings. It may find applications in various scenarios including underwater communication, energy harvesting, and acoustic sensing.

Measurements of radial profile of isotope density ratio using bulk charge exchange spectroscopy.

A bulk charge exchange spectroscopy (BCXS) system using a grism (grating prism) spectrometer has been applied to measure the profile of the deuterium (D) fraction in deuterium and hydrogen (H) mixture plasma in the Large Helical Device. The observed spectrum can be fitted with four Gaussian functions successfully by reduction of free parameters for the least-squares fit. The plasma flow velocity and ion temperature profile measured by charge exchange spectroscopy using carbon impurity are used for estimation of the wavelength shift of hot components to reduce the free parameter. The ion temperature is used to estimate the apparent wavelength shift due to the energy dependent emission cross section only and is not used to set the Doppler width for H and D in the fitting. The sensitivity of the evaluated D fraction on the velocity is increased for a higher D fraction. The error of the D fraction is calculated from the error in the fitted parameter and sensitivity on the velocity of the hot component. The difference in the profile and time trace of the D fraction with D pellet and H pellet injection was observed clearly by BCXS using a grism spectrometer.

Comparison of Physical and Numerical Model on Dam Break Flood Wave Propagation in Horizontal Channel

This paper presents experimental results and the development of a numerical model for simulating dam break flood wave propagation. Floods caused by dam breaks have special flow characteristics due to potential energy caused by upstream and downstream elevation differences, and very high flow rates, from the collapse of the dam wall. The physical model is built on a horizontal channel, with 10 meters length and 1-meter width. The reservoirs used are upstream and downstream. Channels used are made of steel materials with negligible friction. The building used is made from wood with a volume of 10x10x40 cm. Flood wave propagation is modelled as a flash flood due to the mass movement of water in large quantities with the sudden opening of water gates. As the initial conditions, the door will be closed. On the upstream of the door, given the initial conditions of water level. Physical models result is used as calibration of numerical models. The developed numeric model is open foam that produces 3D modeling. The result of the physical model and numerical model show the highest flow velocity and good agreement of the pattern of flow velocity profiles during the first 3 seconds. The comparison of the Numerical model and Physical Model indicates whether the numerical model is feasible for use in dam-break modeling. For better results, it is necessary to develop a further model. Solutions to this physical and numerical model can be part of the mitigation effort in case the disaster phenomenon occurs.

Gas–Liquid Taylor Flow Characteristics in a Fractal Microchannel Network during Numbering-up and Sizing-up

In the present study, the characteristics of gas-liquid Taylor flow in a fractal microchannel network were investigated by numerical modeling and experiments. With perpendicular gas intake, the fractal design methodology resulted in uniform flow distribution. Unstable Taylor flow and saddle-shaped velocity profile were observed in a high-level branch with 0.3 mm width. The liquid slug exhibited different flow fields during splitting in the bifurcations of different levels. The significant size effects were further investigated in four channels representing different sizes (0.3, 0.6, 1.2, and 2.4 mm) via a μ-PIV and high-speed camera. The normalized slug length (LS/W) increased with the increasing gas-liquid flow rate ratio (jG/jL), while the bubble length (LB/W) followed an opposite trend. The stability of the gas-liquid Taylor flow pattern became worse when the gas velocity increased beyond a certain value (Reynolds number Re > 220) under the microscale effect. Two typical counter rotating vortices were observed in the liquid slug, and the swirling strength increased exponentially with the jG/jL. It was found that both the velocity profile in the 0.3 mm channel deviated from the laminar flow. Particularly, a flow field similar to turbulence was observed in the 0.3 mm channel when the jG/jL reached 4. This work quantified the significant size effect in micro- and millichannels, providing theoretical basis for the effective scale-up of the microreactor.

Prediction of velocity profile of water based copper nanofluid in a heated porous tube using CFD and genetic algorithm

The heat transfer improvements by simultaneous usage of the nanofluids and metallic porous foams are still an attractive research area. The Computational fluid dynamics (CFD) methods are widely used for thermal and hydrodynamic investigations of the nanofluids flow inside the porous media. Almost all studies dedicated to the accurate prediction of the CFD approach. However, there are not sufficient investigations on the CFD approach optimization. The mesh increment in the CFD approach is one of the challenging concepts especially in turbulent flows and complex geometries. This study, for the first time, introduces a type of artificial intelligence algorithm (AIA) as a supplementary tool for helping the CFD. According to the idea of this study, the CFD simulation is done for a case with low mesh density. The artificial intelligence algorithm uses learns the CFD driven data. After the intelligence achievement, the AIA could predict the fluid parameters for the infinite number of nodes or dense mesh without any limitations. So, there is no need to solve the CFD models for further nodes. This study is specifically focused on the genetic algorithm-based fuzzy inference system (GAFIS) to predict the velocity profile of the water-based copper nanofluid turbulent flow in a porous tube. The most intelligent GAFIS could perform the most accurate prediction of the velocity. Hence, the intelligence of GAFIS is tested for different values of cluster influence range (CIR), squash factor(SF), accept ratio (AR) and reject ratio (RR), the population size (PS), and the percentage of crossover (PC). The maximum coefficient of determination (~ 0.97) was related to the PS of 30, the AR of 0.6, the PC of 0.4, CIR of 0.15, the SF 1.15, and the RR of 0.05. The GAFIS prediction of the fluid velocity was in great agreement with the CFD. In the most intelligent condition, the velocity profile predicted by GAFIS was similar to the CFD. The nodes increment from 537 to 7671 was made by the GAFIS. The new predictions of the GAFIS covered all CFD results.

Solving nonlinear differential equations with differentiable quantum circuits

We propose a quantum algorithm to solve systems of nonlinear differential equations. Using a quantum feature map encoding, we define functions as expectation values of parametrized quantum circuits. We use automatic differentiation to represent function derivatives in an analytical form as differentiable quantum circuits (DQCs), thus avoiding inaccurate finite difference procedures for calculating gradients. We describe a hybrid quantum-classical workflow where DQCs are trained to satisfy differential equations and specified boundary conditions. As a particular example setting, we show how this approach can implement a spectral method for solving differential equations in a high-dimensional feature space. From a technical perspective, we design a Chebyshev quantum feature map that offers a powerful basis set of fitting polynomials and possesses rich expressivity. We simulate the algorithm to solve an instance of Navier-Stokes equations, and compute density, temperature and velocity profiles for the fluid flow in a convergent-divergent nozzle.

Effects of stagnating and thermal shielding of an upstream promoter on forced convection of flow past a square cylinder in a channel

This work performs a direct simulation on forced convection heat transfer of flow past a square cylinder in a channel with an upstream promoter. The promoter is small in size that the incoming flow is stagnated and heated, thus the flow in the gap between the promoter and main cylinder keeps steady and the heating by the main cylinder gets weak as it develops downstream. The objective of the present study is to explore the effects of two parameters, i.e., Reynolds number and gap ratio, on the thermal and flow characteristics for Re = 70-140 and GR = 2-8. The effects of the two parameters are presented and analyzed by the thermal and flow fields, variations of global characteristics quantities, local heat transfer characteristics, patterns of flow in the gap and near-wake region, and temperature on the channel walls. We emphasize both time-averaged and fluctuating quantities to reflect the mean and pulsating characteristics of the flow. Numerical results reveal that although the promoter produces a steady flow in the gap, it alters the velocity profile of the gap flow and consequently changes the shearing properties, thus influences the flow around and even in the wake downstream of the main cylinder. In general, the small promoter partially stabilizes the wake flow and reduces the amplitude of fluctuating forces acting on the main cylinder compared with the single cylinder configuration, and the stabilization is more remarkable for small gap ratios. However, the fluctuation of heat transfer rate on the surface of main cylinder may increase. A further analysis indicates that as the promoter is placed close to the main cylinder, the recovery rate of deficit wake flow is slower and the fluctuating amplitude of velocity and temperature is relatively smaller due to the stabilized flow.

Investigation on laminar pipe flow of a non-Newtonian Carreau-Extended fluid

Many fluids used in petroleum and chemical industries are generally described as complex systems that exhibit time-independent non-Newtonian behavior. To adequately represent the rheological behavior of an oil-tolerant and salt-resistant aqueous foam system, a Carreau-Extended (Carreau-E) rheological model, which includes a yield stress, a shear-thinning parameter and a time constant, has been established based on Carreau and Herschel-Bulkley models. In the present study, generalized Reynolds number definitions are proposed for laminar and fully developed pipe flow of non-Newtonian fluids (Carreau-E, Carreau, Herschel-Bulkley and Bingham fluids). Perturbation solutions for pipe flow of a Carreau-E fluid are obtained and their ranges of validity in the problem parameter space are identified. The quantitative effects of rheological parameters (e.g., yield stress, time constant, shear-thinning parameter) and flow parameters, (e.g., pressure gradient, pipe radius) on the velocity profile and flow rate in pipe flow of a Carreau-E fluid are explored. The results obtained for the flow characteristics can be applied or extended for other types of non-Newtonian fluid flow encountered in practical applications.

Evaluation of wall functions for RANS turbulence models by unsteady lid-driven cavity flow

Turbulence models do not perform well near walls because the Reynolds number in this interesting area is low. The wall functions and the advantage method can be efficiently used to model fluid flow at the near wall region. The Reynolds averaged Navier-Stokes turbulence models which had the developed wall functions in Open FOAM, the open source CFD software, were evaluated by the turbulent flow. The 3-D lid-driven cavity flow at the turbulence Reynolds number of 10,000 with various spanwise aspect ratio had been referred to validate these turbulence models. The comparison shown that the realizable k-ɛ turbulence model with the standard k and ɛ wall functions of OpenFOAM was the most powerful model to represent the velocity profile of water flow in the 3-D lid-driven cavities.