Methods In Fluid Mechanics Research Articles

Deciphering ascending thoracic aortic aneurysm hemodynamics in relation to biomechanical properties

The degeneration of the arterial wall at the basis of the ascending thoracic aortic aneurysm (ATAA) is a complex multifactorial process, which may lead to clinical complications and, ultimately, death. Individual genetic, biological or hemodynamic factors are inadequate to explain the heterogeneity of ATAA development/progression mechanisms, thus stimulating the analysis of their complex interplay.Here the disruption of the hemodynamic environment in the ATAA is investigated integrating patient-specific computational hemodynamics, CT-based in vivo estimation of local aortic stiffness and advanced fluid mechanics methods of analysis. The final aims are (1) deciphering the ATAA spatiotemporal hemodynamic complexity and its link to near-wall topological features, and (2) identifying the existing links between arterial wall degeneration and hemodynamic insult. Technically, two methodologies are applied to computational hemodynamics data, the wall shear stress (WSS) topological skeleton analysis, and the Complex Networks theory. The same analysis was extended to the healthy aorta.As main findings of the study, we report that: (1) different spatiotemporal heterogeneity characterizes the ATAA and healthy hemodynamics, that markedly reflect on their WSS topological skeleton features; (2) a link (stronger than canonical WSS-based descriptors) emerges between the variation of contraction/expansion action exerted by WSS on the endothelium along the cardiac cycle, and ATAA wall stiffness. The findings of the study suggest the use of advanced methods for a deeper understanding of the hemodynamics disruption in ATAA, and candidate WSS topological skeleton features as promising indicators of local wall degeneration.

Research on Solving Ionization Equation of High-Speed Aircraft Based on Euler Monte Carlo Method of Fluid Mechanics

Taking the aerodynamic calculation of high-speed aircraft as an example, this paper introduces the modelling and application of computational fluid dynamics in aircraft design. The application of computational fluid dynamics in the design of aircraft is accompanied by the development of computer technology and aerodynamics. From the earlier solution of the Euler equation and the NS equation from a macro perspective, to the solution of the NS equation with chemical reactions and ionization that considers the influence of real gases, and from the micro perspective, the Monte Carlo method is used to directly simulate and solve the gas molecule motion, that is, It represents the development of computational dynamics theory and is also the result of the development of computer technology today. This article discusses the application of computational fluid mechanics, including the selection of mathematical models, the selection of calculation methods, and its application to special problems in aircraft design.

Minimal surfaces on mirror-symmetric frames: a fluid dynamics analogy

Chaplygin’s hodograph method of classical fluid mechanics is applied to explicitly solve the Plateau problem of finding minimal surfaces. The minimal surfaces are formed between two mirror-symmetric polygonal frames having a common axis of symmetry. Two classes of minimal surfaces are found: the class of regular surfaces continuously connecting the supporting frames forming a tube with complex shape; and the class of singular surfaces which have a partitioning film closing the tube in between. As an illustration of the general solution, minimal surfaces supported by triangular frames are fully described. The theory is experimentally validated using soap films. The general solution is compared with the known particular solutions obtained by the Weierstrass inverse method.

Preface: Proceedings of the XXII. International Scientific Conference – The Application of Experimental and Numerical Methods in Fluid Mechanics and Energy 2020

Preface: Proceedings of the XXII. International Scientific Conference – The Application of Experimental and Numerical Methods in Fluid Mechanics and Energy 2020

Editorial: Applications of Infrared Methods in Fluid Mechanics

Editorial: Applications of Infrared Methods in Fluid Mechanics

Modal Analysis of a Laminar-Flow Airfoil under Buffet Conditions at Re = 500,000

An airfoil undergoing transonic buffet exhibits a complex combination of unsteady shock-wave and boundary-layer phenomena, for which prediction models are deficient. Recent approaches applying computational fluid mechanics methods using turbulence models seem promising, but are still unable to answer some fundamental questions on the detailed buffet mechanism. The present contribution is based on direct numerical simulations of a laminar flow airfoil undergoing transonic buffet at Mach number M = 0.7 and a moderate Reynolds number Re = 500, 000. At an angle of attack α = 4∘, a significant change of the boundary layer stability depending on the aerodynamic load of the airfoil is observed. Besides Kelvin Helmholtz instabilities, a global mode, showing the coupled acoustic and flow-separation dynamics, can be identified, in agreement with literature. These modes are also present in a dynamic mode decomposition (DMD) of the unsteady direct numerical solution. Furthermore, DMD picks up the buffet mode at a Strouhal number of St = 0.12 that agrees with experiments. The reconstruction of the flow fluctuations was found to be more complete and robust with the DMD analysis, compared to the global stability analysis of the mean flow. Raising the angle of attack from α = 3∘ to α = 4∘ leads to an increase in strength of DMD modes corresponding to type C shock motion. An important observation is that, in the present example, transonic buffet is not directly coupled with the shock motion.

Analysis of the Project of Innovative Floating Turbine

Abstract The design of a floating, innovative device for river water aeration and conversion of mechanical energy to electrical energy required the analysis of a number of geometrical and dynamic features. Such an analysis may be carried out on the basis of existing methods of numerical fluid mechanics. Models of pressures, forces and torques characteristic for the conversion of watercourse energy were developed for two basic concepts of innovation. These pressures, forces and torques were calculated, designed, and experimentally determined for the variable geometric form and dimensions of the designed working elements of the innovative roller-blade turbine rotor.

FUNNEL FLOW OF A NAVIER-STOKES-FLUID WITH POTENTIAL APPLICATIONS TO MICROPOLAR MEDIA

In this paper foundations are laid for a future solution of a fully coupled flow problem for the micropolar medium undergoing structural change in a funnel-shaped crusher. Initially the fundamental equations of micropolar media are revisited and the problem of structural changes of micropolar media moving in a crusher is explained. Then a review of the current state-of-the-art is presented and a necessary extension of the problem is motivated. The need for using numerical methods of fluid mechanics is emphasized. As a prerequisite for the study of the fully coupled initial boundary value 2D-flow problem of a micropolar fluid the funnel flow of a Navier-Stokes fluid is investigated based on an implicit finite difference scheme using the Thomas algorithm. Numerical results for velocities, stresses, and for the pressure dependence of the funnel flow are presented. The correctness of the algorithm is checked by specializing to the case of a flow through a tunnel of constant cross-section under the influence of gravity, for which an analytical solution is available.

Detecting abnormal crowd behaviors based on the div-curl characteristics of flow fields

This study proposes a divergence-curl-driven framework for the perception of crowd motion states. In this framework, the characteristics of a flow field, divergence and curl, are used to analyze crowd states. As a collective motion, the movement of a pedestrian crowd shows coherent structural properties. By using the methods of fluid mechanics and the feature visualization of flow fields, a physical characteristic descriptor of crowd motion is established that can model the motion state in a crowd flow field. Given the significance of the temporal comparison of motion states for detecting changes in crowds, a method based on the temporal context of motion is presented to measure changes in the distribution of the physical characteristic descriptors of crowd motion. This method can be used to calculate differences in the distribution of the flow field’s physical characteristics between each state and measure these subtle continuous changes on the sample points, thereby obtaining a quantified metric of changes in a crowd’s motion state. Experiments on crowd event datasets demonstrate the effectiveness of our proposed framework for detecting crowd state changes and abnormal activity.

Appending empirical modelling to numerical solution for behaviour characterisation of microalgae biodiesel

With impending economical concerns and fuel crisis, biodiesel produced from microalgae has been proposed as a potential substitute for petroleum fuel. But experimental characterisation of combustion, performance and emission behaviour of biofuel operating under different operating conditions would be resource consuming. Even numerical modelling using computational fluid mechanics methods would be computationally consuming when combinatorics of all operating conditions are considered. In this study, we append empirical modelling to numerical modelling to derive industry feasible solutions. An artificial neural network was trained with responses at limited operating conditions obtained from a software Diesel-RK. Various variables representing combustion, performance and emission behaviour of IC engine were predicted accurately with average r-value of 0.9801 ± 0.0146 for operating conditions defined by blending, loading and fuel injection pressure. Redundancy amongst the system variables was also observed thus indicating to possible reduced empirical models.

A Computing Method for Sand Inrush Quantity through a Borehole in Longde Coal Mine

A quicksand disaster through a borehole occurred in Longde coal mine. A lot of aeolian sand, the volume of which is between 310,000 m3 and 380,000 m3, has submerged into the underground space in about 70.5 h. The volume flux of quicksand cannot be calculated accurately by the empirical method. Based on the method of fluid mechanics, an all-purpose computing method for quicksand disaster through a borehole was proposed. The result shows that the inrush volume of sand into underground space was between 310,000 m3 and 350,000 m3, which was consistent with the actual result. To apply and popularize this method, the impact laws of water yield properties of an aquifer on the volume flux were discussed. The all-purpose computing method can be suitably used for the volume flux calculation of quicksand disaster through the borehole.

Dimensional analysis in the venous system

Dimensional analysis, a standard method of Fluid Mechanics, was applied to the field of venous hemodynamics. Three independent physical quantities, velocity, length and pressure, were chosen and seven other ones were used to derive the non-dimensional terms. The mathematical burden was reduced to the minimum and the attention was focused on the results. Among them, a new formulation of an already known non-dimensional term, recalled the flow-length (FL), was identified and selected for a deeper experimental study.

Rheological measurements for prediction of pumping and squeezing pressures of toothpaste

Methods of non-Newtonian fluid mechanics are applied to predict processability and use of toothpaste, specifically its pumpability through long pipes and squeezability from tubes. The goal is to define procedures which would allow estimating pumping pressure and squeezing force from the data obtained on conventional rotational rheometers which are critical for product development and quality control. 11 commercially available and 28 lab-made model toothpastes are examined. The latter are engineered so as to cover wide range of toothpaste properties ranging from high yield stress products to weakly shear thinning ones by varying the concentration of polymers (xanthan gum and carboxymethyl cellulose) and particulate thickener (silica). Rotational rheometry is represented by narrow-gap Couette concentric cylinders and wide-gap vane-cup geometries. Equilibrium flow curves measured with both geometries are shown to agree, provided proper data processing is used.To assess pumping pressure in long pipes, a capillary rheometer equipped with pipes of different lengths is used. Thus measured pressure drop is compared to the pressures calculated from the equilibrium flow curves. It turns out that while the measurements agree quite well for pastes with higher concentration of silica, there is a systematic overestimation of pressure for pastes with lower concentration of silica and at lower flow rate. A possible explanation for this observation is the presence of wall slippage presumably caused by migration of silica from the pipe wall. This is found to be consistent for the calculations with slip boundary conditions.Vane-cup geometry is used to measure start-up curves from the state of rest which are more representative of tube squeezing during usage. A tube extrusion apparatus is used to quantify squeezability in terms of the force required to pull the tube through two rollers while squeezing toothpaste out of their tubes. Thus measured force correlates with the squeezing pressure calculated using the flow curves measured from the rest.

Preface: Proceedings of the XXI. International Scientific Conference - The Application of Experimental and Numerical Methods in Fluid Mechanics and Energy 2018

Preface: Proceedings of the XXI. International Scientific Conference - The Application of Experimental and Numerical Methods in Fluid Mechanics and Energy 2018

Rapid Calculation Method Study and Realization for Wind Load of Ship-Borne Satellite Antenna

For antennas working in exposed environment, wind load is one of the main loads that must be taken into consideration. Wind load can not only directly impact on the structural strength of antenna, but also make actuating shaft of servo system bear wind torque disturbance which may indirectly affect the tracking accuracy of antenna servo system. This paper completed numerical computation on the wind loads of antenna at different wind speeds, angles of wind approach and angles of pitch based on method of computational fluid mechanics, hence the velocity fluid fields, pressure distribution on reflecting surface and moments of antenna under various posture situations were obtained and a sample database has been formed. According to the weather and ship navigation situation, rapid calculation of the wind load and moment born by antenna realized through ternary three-order curvilinear interpolation algorithm can effectively solve the problem of rapidly calculating the wind load of ship-borne satellite antenna. Moreover, with the sample database formed according to the images and moment data obtained from computation, the wind loads and moment parameters of antenna under all working conditions were obtained through ternary three-order interpolation algorithm, so as to realize the rapid calculation method for the wind loads of antenna under all working conditions.

Performance assessment of cooling systems in data centers; Methodology and application of a new thermal metric

This paper introduces a comprehensive cooling index to assess performance of cooling systems in data centers and demonstrates its application on a real case by using CFD (computational fluid mechanics) method. The proposed methodology provides a metric for comparing and ranking of the cooling efficiency of the air distribution configurations among available designs alternatives.

Flow Simulation of Suspension Bridge Cable Based on Lattice-Boltzmann Method

Suspension bridge is a kind of bridge which uses cables as the main bearing structure. Suspension bridge has the characteristics of saving materials and weak stiffness. With the increase of the span of suspension bridge, wind induced vibration has resulted in injury of several suspension bridges, which leads to a significant loss. Thus, it is imperative to study the wind vibration mechanism of cables. As for this problem, this paper based on motion theory of mesoscopic particles performs flow simulation of cables by LBM which is different from traditional computing method of fluid mechanics. By calculating the distribution function of the distribution on the grid of uniform flow field, the macroscopic motion law of the flow field around cables can be obtained, which can provide reference for wind resistant design of suspension.

Enablers for high‐order level set methods in fluid mechanics

SummaryIn the context of numerical simulations of multiphysics flows, accurate tracking of an interface and consistent computation of its geometric properties are crucial. In this paper, we investigate a level set technique that satisfies these requirements and ensures local third‐order accuracy on the level set function (near the interface) and first‐order accuracy on the curvature, even for long‐time computations. The method is developed in a finite differences framework on Cartesian grids. As in usual level set strategies, reinitialization steps are involved. Several reinitialization algorithms are reviewed and mixed to design an accurate and fast reinitialization procedure. When coupled with a time evolution of the interface, the reinitialization procedure is performed only when there are too large deformations of the isocontours. This strategy limits the number of reinitialization steps and shows a good balance between accuracy and computational cost. Numerical results compare well with usual level set strategies and confirm the necessity of the reinitialization procedure, together with a limited number of reinitialization steps. Copyright © 2015 John Wiley & Sons, Ltd.

Reservoir Modeling for Flow Simulation by Use of Surfaces, Adaptive Unstructured Meshes, and an Overlapping-Control-Volume Finite-Element Method

SummaryWe present new approaches to reservoir modeling and flow simulation that dispose of the pillar-grid concept that has persisted since reservoir simulation began. This results in significant improvements to the representation of multiscale geologic heterogeneity and the prediction of flow through that heterogeneity. The research builds on more than 20 years of development of innovative numerical methods in geophysical fluid mechanics, refined and modified to deal with the unique challenges associated with reservoir simulation.Geologic heterogeneities, whether structural, stratigraphic, sedimentologic, or diagenetic in origin, are represented as discrete volumes bounded by surfaces, without reference to a predefined grid. Petrophysical properties are uniform within the geologically defined rock volumes, rather than within grid cells. The resulting model is discretized for flow simulation by use of an unstructured, tetrahedral mesh that honors the architecture of the surfaces. This approach allows heterogeneity over multiple length-scales to be explicitly captured by use of fewer cells than conventional corner-point or unstructured grids.Multiphase flow is simulated by use of a novel mixed finite-element formulation centered on a new family of tetrahedral element types, PN(DG)–PN+1, which has a discontinuous Nth-order polynomial representation for velocity and a continuous (order N +1) representation for pressure. This method exactly represents Darcy-force balances on unstructured meshes and thus accurately calculates pressure, velocity, and saturation fields throughout the domain. Computational costs are reduced through dynamic adaptive-mesh optimization and efficient parallelization. Within each rock volume, the mesh coarsens and refines to capture key flow processes during a simulation, and also preserves the surface-based representation of geologic heterogeneity. Computational effort is thus focused on regions of the model where it is most required.After validating the approach against a set of benchmark problems, we demonstrate its capabilities by use of a number of test models that capture aspects of geologic heterogeneity that are difficult or impossible to simulate conventionally, without introducing unacceptably large numbers of cells or highly nonorthogonal grids with associated numerical errors. Our approach preserves key flow features associated with realistic geologic features that are typically lost. The approach may also be used to capture near-wellbore flow features such as coning, changes in surface geometry across multiple stochastic realizations, and, in future applications, geomechanical models with fracture propagation, opening, and closing.

Variational Approach for Resolving the Flow of Generalized Newtonian Fluids in Circular Pipes and Plane Slits

We use a generic and general variational method to obtain solutions to the flow of generalized Newtonian fluids through circular pipes and plane slits. The new method is not based on the use of the Euler-Lagrange variational principle and hence it is totally independent of our previous approach which is based on this principle. Instead, the method applies a very generic and general optimization approach which can be justified by the Dirichlet principle although this is not the only possible theoretical justification. The results that were obtained from the new method using nine types of fluid are in total agreement, within certain restrictions, with the results obtained from the traditional methods of fluid mechanics as well as the results obtained from the previous variational approach. In addition to being a useful method in its own for resolving the flow field in circular pipes and plane slits, the new variational method lends more support to the old variational method as well as for the use of variational principles in general to resolve the flow of generalized Newtonian fluids and obtain all the quantities of the flow field which include shear stress, local viscosity, rate of strain, speed profile, and volumetric flow rate.