Three-dimensional Flow Analysis Research Articles

Numerical approach of variable thermophysical features of dissipated viscous nanofluid comprising gyrotactic micro-organisms

This article addresses the heat and mass transport phenomena by performing a theoretical analysis of three-dimensional viscous fluid flow containing gyrotactic micro-organisms over a nonlinear stretched surface. Variable magnetic field is considered normal to the stretched surface to control the fluid flow. Thermal transportation is discussed in view of variable thermal conductivity. Variable characteristics of mass diffusion along with chemical reaction are incorporated in mass transportation. Darcy–Forchheimer expression is used to characterise the porous medium. Also, Brownian motion and thermophoresis are incorporated to enhance the diffusion. The governing partial differential equations (PDEs) are derived using boundary layer analysis by assuming small magnetic Reynolds number. Appropriate transformation is used to convert complex system of coupled PDEs into nonlinear ordinary differential equations (ODEs). Transformed problem is then tackled analytically using optimal homotopic procedure. Reliability of the suggested scheme is presented through error reduction table and also by comparing the obtained solution with the published ones. Graphs and tables are prepared to observe the impact of parameters on physical variables. Dimensionless stresses and rate of heat transfer are computed numerically. It has been observed that larger values of Brownian diffusion and thermophoresis increase the fluid temperature. Moreover, dimensionless stresses and rate of heat transfer are computed to check the reliability of the proposed procedure. These values are clearly in an excellent agreement with the previous findings reported in literature.

Numerical analysis of three-dimensional MHD flow of Casson nanofluid past an exponentially stretching sheet

The convective three dimensional electrically conducting Casson nanofluid flow over an exponentially stretching sheet embedded in a saturated porous medium and subjected to thermal as well as solutal slip in the presence of externally applied transverse magnetic field (force-at-a-distance) is studied. The heat transfer phenomenon includes the viscous dissipation, Joulian dissipation, thermal radiation, contribution of nanofluidity and temperature dependent volumetric heat source. The study of mass diffusion in the presence of chemically reactive species enriches the analysis. The numerical solutions of coupled nonlinear governing equations bring some earlier reported results as particular cases providing a testimony of validation of the present study. The important findings are reported as Casson fluid contributes to accelerate the processes of momentum diffusivity but decelerates the thermal diffusivity. The effects of respective Biot numbers in temperature and concentration distributions are significant whereas cross effects are not. Further, the existence of chemical reaction stabilizes the characteristics of rate coefficients at the surface.

Aerodynamic forces and three-dimensional flow structures in the mean wake of a surface-mounted finite-height square prism

Different flow models have been proposed for the flow around surface-mounted finite-height square prisms, but there is still a lack of consensus about the origin and connection of the streamwise tip vortices with the other elements of the wake. This numerical study was performed to address this gap, in addition to clarifying the relationship of the near-wake structures with the far wake and the near-wall flow, which is associated with the fluid forces. A large-eddy simulation approach was adopted to solve the flow around a surface-mounted finite-height square prism with an aspect ratio of AR = 3 and a Reynolds number Re = 500. The mean drag and normal forces and the bending moment for the prism were quantitatively compared in terms of skin-friction and pressure contributions, and related to the near-wall flow. Both three-dimensional visualizations and planar projections of the time-averaged flow field were used to identify, qualitatively, the main structures of the wake, including the horseshoe vortex, corner vortices and regions of high streamwise vorticity in the upper part of the wake. These features showed the same qualitative behavior as reported in high Reynolds number studies. It was found that some regions of high streamwise vorticity magnitude, like the tip vortices, are associated with the three-dimensional bending of the flow, and the tip vortices did not continuously extend to the free end of the prism. The three-dimensional flow analysis, which integrated different observations of the flow field around surface-mounted finite-height square prisms, also revealed that the mean near-wake structure is composed of two sections of different origin and location of dominance.

In Memoriam: Professor Ephraim Maurice Sparrow

In Memoriam: Professor Ephraim Maurice Sparrow

On the quest for generalized Hamiltonian descriptions of 3D-flows generated by the curl of a vector potential

We examine Hamiltonian analysis of three-dimensional advection flow [Formula: see text] of incompressible nature [Formula: see text] assuming that the dynamics is generated by the curl of a vector potential [Formula: see text]. More concretely, we elaborate Nambu–Hamiltonian and bi-Hamiltonian characters of such systems under the light of vanishing or non-vanishing of the quantity [Formula: see text]. We present an example (satisfying [Formula: see text]) which can be written as in the form of Nambu–Hamiltonian and bi-Hamiltonian formulations. We present another example (satisfying [Formula: see text]) which we cannot able to write it in the form of a Nambu–Hamiltonian or bi-Hamiltonian system while it can be manifested in terms of Hamiltonian one-form and yields generalized or vector Hamiltonian equations [Formula: see text].

Design and manufacturing a small-scale radial-inflow turbine for clean organic Rankine power system

With growing on the energy demand and availability of the low-grade temperature heat source, the organic Rankine cycle as a power system can be efficiently utilized to generate electricity. The turbine design and its performance have the main impact on determining the system power and overall system efficiency. Therefore, design a small-scale organic Rankine system requires the development of an appropriate turbine. To achieve this aim, this work offers an innovative complete design method to develop a radial-inflow turbine for small-scale organic Rankine cycle power applications, which includes a preliminary design (i.e. one-dimensional design calculation phase) and a three-dimensional flow analysis using the computational fluid dynamic technique. A thermodynamic analysis of the organic Rankine cycle was integrated with the design methodology. Where the three-dimensional geometry model was built based on the thermodynamic and aerodynamic design, and then was imported into the ANSYS-CFX software to conduct viscous numerical simulations. The optimum design of the radial-inflow turbine was manufactured using a three-dimensional printing (pioneering) technique, and the experimental testing was conducted at off-design points to validate the turbine design.The evaluation of the turbine’s performance (efficiency and power) was presented under design and off-design points in terms of rotational speeds, expansion ratios, and inlet temperatures with five different organic fluids. The turbine numerical results showed that R600 as a working fluid has a higher predicted turbine efficiency of 78.32% and power of 4.8 kW with cycle thermal efficiency of 9.15% compared with 8.045% for R245fa. Depending on the experimental results at off-design points, the highest cycle thermal efficiency of 4.25% with a turbine efficiency of 45.22% was achieved. These results assured the precision of the proposed PD methodology at off-design points in making performance maps of the turbine.

Three-dimensional analysis of heat transfer in a channel provided with solid baffle, single and double perforation

PurposeThe purpose of this paper is to present a three-dimensional (3D) analysis of the laminar flow of air and the conjugate heat transfer in a pipe of rectangular cross-section with a solid or perforated deflector inserted on the lower wall.Design/methodology/approachTo this end, by using the finite volume method, the conservation equations for mass, momentum and energy are solved numerically. Two cases of “single and double” perforation were studied and compared with that of the solid case for a range of Reynolds numbers ranging from 140 to 840. The velocity and temperature profiles were plotted and interpreted on three different sections placed sequentially upstream, mid-stream and downstream of the deflector. Total heat exchange at the bottom wall, outlet fluid temperature, perforated PFE deflector performance and pressure loss is presented for different cases studied and for different Reynolds numbers.FindingsThe results show that although the perforated deflector improves the heat transfer, it also results in additional pressure losses; the study also showed the existence of a limiting velocity beyond which the perforation effect on the improvement of the heat exchange decreases until the same performance of the solid deflector is achieved.Originality/valueThe main originality of this work is to show a 3D analysis for a perforated baffle as heat exchanger application.

Study of Mini Channel Heat Sink with Different Internal Configuration

In this paper a numerical analysis of three-dimensional laminar flow through rectangular channel heat sinks of different geometric configuration is presented and a comparison of thermal performance among the heat sinks is discussed. Liquid water was used as coolant in the aluminum made heat sink with a glass cover above it. The aspect ratio (section height to width) of rectangular channels of the mini-channel heat sink was 0.33. A heat flux of 20 W/cm2 was continuously applied at the bottom of the channel with different inlet velocity for Reynold’s number ranging from 150 to 1044. Interconnectors and obstacles at different positions and numbers inside the channel were introduced in order to enhance the thermal performance. These modifications cause secondary flow between the parallel channels and the obstacles disrupt the boundary layer formation of the flow inside the channel which leads to the increase in heat transfer rate. Finally, Nusselt number, overall thermal resistance and maximum temperature of the heat sink were calculated to compare the performances of the modified heat sinks with the conventional mini channel heat sink and it was observed that the heat sink with both interconnectors and obstacles enhanced the thermal performance more significantly than other configurations. A maximum of 36% increase in Nusselt number was observed (for Re =1044).

Coupled Numerical Analysis of Three-Dimensional Unsteady Flow with Pitching Motion of Reentry Capsule—Investigation of the Third Harmonics of the Aerodynamic Force—

Coupled Numerical Analysis of Three-Dimensional Unsteady Flow with Pitching Motion of Reentry Capsule—Investigation of the Third Harmonics of the Aerodynamic Force—

Full three-dimensional Poynting vector flow analysis of great field-intensity enhancement in specifically sized spherical-particles

The Poynting vector plays a key role in electrodynamics as it is directly related to the power and the momentum carried by an electromagnetic wave. Based on the Lorenz-Mie theory, we report on the focusing effect of a spherical particle-lens by properly analysing the Poynting vector maps. Conventional two-dimensional (2D) maps showing Poynting vector magnitude and direction in a given plane cannot deliver information on three-dimensional (3D) directivity and vectorisation in key regions of singularities, such as vortexes and saddle points, due to poor expressiveness. In this article, an analytical 3D mapping technology is utilised to track the field-features passing through the singularities of the distribution of the Poynting vector in a spherically dielectric mesoscale particle-lens. We discovered that the spheres with the certain size parameters can stimulate extremely large field-intensity at singularities and then form two circular hotspots around the sphere poles. An astonishing large ‘heart-shape’ 3D Poynting vector circulation, which cannot be predicted by conventional 2D mapping analysis, is found to provide a great angular variation within an enormous range in these spheres. We anticipate that this effect will contribute to the field-enhancement phenomena, such as surface enhances Raman scattering, surface enhances absorption, super-resolution imaging and others.

Three-Dimensional Thermo-Poroelastic Modeling and Analysis of Flow, Heat Transport and Deformation in Fractured Rock with Applications to a Lab-Scale Geothermal System

Fractures and other discontinuities, such as bedding planes, and faults, usually act as highly permeable flow paths, dominating subsurface fluid and heat transport, which is of importance in developing underground energy resources. We investigate coupled transport and fracture deformation/propagation within the framework of the theory of thermo-poroelasticity. A 3D finite element method is developed and utilized to discretize the governing equations. To simulate the thermo-hydro-mechanical behavior of the fracture/matrix system, a special zero-thickness interface element is implemented based on the cohesive zone model (CZM), to simulate both tensile and shear failure. The fluid flux/heat exchange between the fractures and the surrounding permeable rock matrix is determined by fluid/heat transfer coefficients satisfying mass and energy balance across the interior boundaries, and allowing for temperature and pressure drop across the interface. Numerical analyses are performed to verify the model and to illustrate fundamental phenomena observed in the laboratory. Lab-scale fracturing and circulation experiments are studied in detail, revealing the role of hydro-thermo-mechanical properties and coupled processes.

A very-high resolution (20m) measurement-based dust emissions and dispersion modeling approach for the Oceano Dunes, California

This study shows the results from very high-resolution (20 m) dust emissions and transport simulations for the Oceano Dunes State Vehicular Recreation Area (ODSVRA), a coastal sand dune complex located in San Luis Obispo County, California. Field data from an enhanced observation period carried out in May–July 2013 helped estimate the emissions and flow conditions over the dune field. Emissions are based on a comprehensive emissions grid developed from in-situ measurements using the Portable In-Situ Wind ERosion Lab (PI-SWERL). PI-SWERL estimates the potential for a soil surface to produce PM10 dust emissions for a range of wind speeds. This approach provided a well-determined PM10 emissions field as a function of time and space. Wind and turbulence fields were estimated using the CALMET diagnostic meteorological model constrained with surface stations, upper air soundings, buoys, and the North American Reanalysis data. Hourly, three-dimensional wind flow and instability objective analysis fields were developed at 20 m resolution in order to consider the complex flow over realistic dune morphology, land use/land cover and terrain characteristics over and around the Oceano Dunes. The dust dispersion simulations were performed using a computationally efficient and vectorized Lagrangian Stochastic Particle Dispersion Model driven by the CALMET output and the PI-SWERL time-space variable emissions. The dispersion model is based on the Langevin formulation and includes the turbulent diffusion and stochastic particle motion (of millions of particles) in the inertial sub-range, and assuming particles as discrete units neglecting deposition. The model estimates diffusion of particles from an initial particle releases that scale according to the PI-SWERL time-variable emissions estimates. Results were then tested at two independent-downwind locations, with positive correlations for flow conditions (R2 = 0.89) and similar receptor PM10 concentrations (R2 = 0.85). Evaluations against those observations during mean flow conditions as well as for elevated dust events suggest that the model framework can capture the spatial and temporal characteristics of mean day-to-day and diurnal PM10 variability. In this study we describe the details of the model framework and its performance as well as its implementation to locate the dust sources that have the strongest impact in the receptor sites and to evaluate the impact of different dust reduction strategies used at the ODSVRA to mitigate PM10 at downwind receptors.

Three-dimensional Flow Analysis of Polyurethane Foaming Process

Three-dimensional Flow Analysis of Polyurethane Foaming Process

Computational and asymptotic methods for three-dimensional boundary-layer flow and heat transfer over a wedge

This paper is devoted to mathematical analysis of three-dimensional boundary-layer flow and heat transfer over a wedge. The boundary layer is formed due to the flow of a viscous and incompressible fluid and grows downstream along the walls of the wedge. This is appropriately approximated by a power of distances along both lateral directions. This analysis introduces a shear-to-strain-rate parameter $$\gamma$$ in the study which plays an essential role in three-dimensional boundary-layer study. A set of boundary-layer equations along with the conservation of energy has been transformed into a coupled nonlinear ordinary differential equations. Two methods are employed. The fluid–wedge interaction problem is solved in the circumstances where the equations are linearized and obtained the solutions in terms of confluent hypergeometric functions, and otherwise, the full-nonlinear problem numerically using the Keller-box method. In the former case, the results of eigenfunction analysis that is based on asymptotic study of the problem qualitatively support the latter numerical results. In either methods, the existence of solutions and range of parameter domain depending on various physical quantities is successfully analyzed. The two different approaches give good agreement with each other in predicting the velocity and temperature profiles in three-dimensional boundary layer. However, both approaches show that a solution to the problem exist only $$-\,1< \gamma < \infty$$ . Since the Reynolds number is asymptotically large, the flow clearly divides into two regions showing the effects of viscosity and thermal conductivity. The velocity and thermal profiles are found to be benign. Flow always attached to the wedge surfaces and, thus, related thicknesses are becoming thinner. Extensive comparisons of the various results are made and a possible explanation on the results is discussed in some detail.

MHD Boundary Layer Flow of Carreau Fluid over a Convectively Heated Bidirectional Sheet with Non-Fourier Heat Flux and Variable Thermal Conductivity

In the present exploration, instead of the more customary parabolic Fourier law, we have adopted the hyperbolic Cattaneo–Christov (C–C) heat flux model to jump over the major hurdle of “parabolic energy equation”. The more realistic three-dimensional Carreau fluid flow analysis is conducted in attendance of temperature-dependent thermal conductivity. The other salient impacts affecting the considered model are the homogeneous-heterogeneous (h-h) reactions and magnetohydrodynamic (MHD). The boundary conditions supporting the problem are convective heat and of h-h reactions. The considered boundary layer problem is addressed via similarity transformations to obtain the system of coupled differential equations. The numerical solutions are attained by undertaking the MATLAB built-in function bvp4c. To comprehend the consequences of assorted parameters on involved distributions, different graphs are plotted and are accompanied by requisite discussions in the light of their physical significance. To substantiate the presented results, a comparison to the already conducted problem is also given. It is envisaged that there is a close correlation between the two results. This shows that dependable results are being submitted. It is noticed that h-h reactions depict an opposite behavior versus concentration profile. Moreover, the temperature of the fluid augments for higher values of thermal conductivity parameters.

Hyperbolicity, shadowing directions and sensitivity analysis of a turbulent three-dimensional flow

This paper uses compressible flow simulation to analyse the hyperbolicity, shadowing directions and sensitivities of a weakly turbulent three-dimensional cylinder flow at Reynolds number 525 and Mach number 0.1. By computing the first 40 covariant Lyapunov vectors (CLVs), we find that unstable CLVs are active in the near-wake region, whereas stable CLVs are active in the far-wake region. This phenomenon is related to hyperbolicity since it shows that CLVs point to different directions; it also suggests that for open flows there is a large fraction of CLVs that are stable. However, due to the extra neutral CLV and the occasional tangencies between CLVs, our system is not uniform hyperbolic. By the non-intrusive least-squares shadowing (NILSS) algorithm, we compute shadowing directions and sensitivities of long-time-averaged objectives. Our results suggest that shadowing methods may be valid for general chaotic fluid problems.

Machine-learned super-resolution analysis of three-dimensional turbulent channel flow

Machine-learned super-resolution analysis of three-dimensional turbulent channel flow

Acute Posterior Multifocal Placoid Pigment Epitheliopathy: A Case Report with Optical Coherence Tomography Angiography Images

The Acute Posterior Multifocal Placoid Pigment Epitheliopathy (APMPPE) is a rare acquired idiopathic inflammatory disease that affects the choriocapillaris and external retinal layers. It usually presents as a bilateral, asymmetric, acute, visual loss in young healthy adults. The etiology of APMPPE is unknown and the pathogenesis is controversial, but it is thought that an obstructive vasculitis is the underlying disorder, causing non-perfusion of the retina layers. Funduscopic evaluation is characterized by multiple yellow-white lesions at the level of the retinal pigment epithelium (RPE) and choriocapillaris. Recently, noninvasive techniques of optical coherence tomography angiography (OCT-A) have provided a detailed three-dimensional analysis of blood flow in the retina’s layers and the inner choroid. To our knowledge there have been only a few reports describing OCT-A findings in APMPPE, so we describe a case that might contribute to the growing evidence of a primary choroidal involvement with secondary damage to the overlying RPE and the outer retinal layers, rather than a primary RPE inflammatory etiology, as was originally thought.

Research of coupled wall conduction effects on forced and natural circulation of LBE in CLEAR-S

The lead based reactor concept is considered to be the most promising reactor option for the Accelerator Driven Subcritical (ADS) system. Lead based reactor engineering validation facility CLEAR-S is a large scale integrated non-nuclear pool type facility which has been built to provide a unique experimental platform for full-scale prototype components test of lead based reactors. In this article, three-dimensional steady state analysis of flow in the hot and cold pools of CLEAR-S was carried out by using computational fluid dynamics (CFD) code FLUENT during forced and natural circulation conditions. The results showed that the simulation had a good agreement with the design parameters of CLEAR-S and the temperature profile was uniform in the whole domain of the hot and cold pools without considering any conduction through the coupled walls. The temperature distribution in the hot and cold pools became non-uniform with the coupled wall conduction and thermal stratification was observed in the cold and hot pools near the bottom wall of the hot pool. This non-uniform distribution of temperature could cause thermal stresses on equipment, which is dangerous for the integrity of the system. During natural circulation conditions, the coupled wall conduction enhanced the natural circulation and kept the hot pool at a relatively low temperature because the cold pool cooled the hot pool through heat transfer between the walls of the hot and cold pools. Therefore, wall conduction has some advantages and disadvantages as it enhances the natural circulation on one hand but disturbs temperature uniformity on the other hand.

Fast identification of transonic buffet envelope using computational fluid dynamics

PurposeThis paper aims to present a numerical method based on computational fluid dynamics that allows investigating the buffet envelope of reference equivalent wings at the equivalent cost of several two-dimensional, unsteady, turbulent flow analyses. The method bridges the gap between semi-empirical relations, generally dominant in the early phases of aircraft design, and three-dimensional turbulent flow analyses, characterised by high costs in analysis setups and prohibitive computing times.Design/methodology/approachAccuracy in the predictions and efficiency in the solution are two key aspects. Accuracy is maintained by solving a specialised form of the Reynolds-averaged Navier–Stokes equations valid for infinite-swept wing flows. Efficiency of the solution is reached by a novel implementation of the flow solver, as well as by combining solutions of different fidelity spatially.FindingsDiscovering the buffet envelope of a set of reference equivalent wings is accompanied with an estimate of the uncertainties in the numerical predictions. Just over 2,000 processor hours are needed if it is admissible to deal with an uncertainty of ±1.0° in the angle of attack at which buffet onset/offset occurs. Halving the uncertainty requires significantly more computing resources, close to a factor 200 compared with the larger uncertainty case.Practical implicationsTo permit the use of the proposed method as a practical design tool in the conceptual/preliminary aircraft design phases, the method offers the designer with the ability to gauge the sensitivity of buffet on primary design variables, such as wing sweep angle and chord to thickness ratio.Originality/valueThe infinite-swept wing, unsteady Reynolds-averaged Navier–Stokes equations have been successfully applied, for the first time, to identify buffeting conditions. This demonstrates the adequateness of the proposed method in the conceptual/preliminary aircraft design phases.