Turbulent Flow Of Incompressible Fluid Research Articles

Employment of roughened absorber palate and jet nozzles with different hole shapes for performance boost of solar-air-heaters

In this study, roughened absorber plate and jet nozzle are simultaneously employed to enhance the efficiency of a solar based air heater. The impact of jet nozzle hole shape is comprehensively investigated for the mentioned system which have not been investigated before. Three-dimensional steady-state simulations of incompressible turbulent fluid flow and heat transfer are performed using the Reynolds-Averaged Navier-Stokes (RANS) equations to model the jet solar air heater (JSAH). Five different jet hole shapes (circular, triangular, square, hexagonal, and rectangular) are examined and results are compared with conventional structure. The thermal and hydraulic performance of the JSAH is assessed using a variety of geometric and operating parameters, including jet diameter ratio (dj/Dh), jet hole streamwise pitch (Lj/Dh), and Re number (Re). The results show that the ratio of (Nu/Nus) initially increases and then decreases as the hydraulic diameter of the jet holes increases. Circular jet holes consistently outperform other shapes, while rectangular and triangular jet holes perform poorly. The pressure penalty (f/fs) decreases with increasing (dj/Dh), with circular jet holes exhibiting the lowest value. Increasing the Reynolds number enhances heat transfer and pumping power but leads to a decrease in (Nu/Nus) and negatively affects the THPP of the JSAH compared to a conventional smooth solar air heater. The study also reveals that the THPP initially increases with streamwise pitch (Lj/Dh) but then declines, following the trend of (Nu/Nus). The results demonstrate up to 4.5 times higher Nusselt numbers with a jet solar air heater versus a smooth solar heater. A maximum thermal-hydraulic performance parameter of 1.64 indicates the proposed design's efficacy. This research furnishes critical insights into optimizing solar air heater performance by examining jet nozzle hole shape, streamwise pitch, and Reynolds number. It enables enhancing thermal efficiency and thermo-hydraulic performance.

Simulation of macrosegregation in continuous casting of steel based on large-eddy simulation turbulence model and meshless solution procedure

The formation of macrosegregation pattern in steel is explored for the continuous casting process. The related solidification problem is described by incompressible turbulent fluid flow, governed by mass, momentum, energy, and species conservation equations. The solid-liquid system is designed in a mixture continuum model formulation, and the mushy region is approximated with the Darcy model. The lever rule describes the formation of microsegregation of carbon. Turbulence is modelled with a large-eddy simulation approach implemented with the Smagorinsky model and van Driest correction. The synthetic isotropic fluctuations of the inlet velocity are generated by the von Karman Pao spectrum. The solution of partial differential equations is implemented locally by using collocation with radial basis functions for spatial discretization and the explicit Euler method for time discretization. The two-dimensional large eddy simulation model solutions are compared to the previously calculated examples obtained with the low-Re k − ε turbulence model.

Development of Three-Dimensional LES Based Meshless Model of Continuous Casting of Steel

A large-eddy simulation (LES) based meshless model is developed for the three-dimensional (3D) problem of continuous casting (CC) of steel billet. The local collocation meshless method based on radial basis functions (RBF) is applied in 3D. The method applies scaled multiquadric (MQ) RBF with a shape parameter on seven nodded local sub-domains. The incompressible turbulent fluid flow is described using mass, energy, and momentum conservation equations and the LES turbulence model. The solidification system is solved with the mixture continuum model. The Boussinesq approximation for buoyancy and the Darcy approximation for porous media are used. Chorin’s fractional step method is used to couple velocity and pressure. The microscopic model is closed with the lever rule model. The LES model is compared to the two-equation Low Re k−ε turbulence Reynolds Averaged Navier–Stokes (RANS) model in terms of temperature, velocity and computational times. The LES model resolves transient character of vortices which RANS-type turbulence models are unable to tackle. The computational cost of LES models is considerably higher than in RANS. On the other hand, it results in a much lower computational cost than the direct numerical simulation (DNS). The paper demonstrates the ability of the method to solve realistic industrial 3D examples. Trivial adjustment of nodal densities, high accuracy, and low numerical diffusivity are the main advantages of this meshless method.

A hardware accelerated unstructured overset method to simulate turbulent fluid flow

Hardware acceleration consists of offloading computational work to devices such as graphics processing units (GPUs) to produce overall speed-up. Algorithms and numerical methods must be constructed to suit the available hardware in order to effectively produce speed-up. In this work a numerical method is presented which can effectively use hardware acceleration to simulate incompressible turbulent fluid flow. The method is an unstructured overset method where unstructured meshes are attached to individual bodies and connected throughout the flow domain to produce a single domain solution through an overset assembly process. The unstructured overset method shown in Horne and Mahesh [1] and Horne and Mahesh [2] was found capable of scaling to O(105) computational cores for O(105) moving bodies in turbulent flow fields while producing accurate flow results. This highly scalable method is modified and extended to effectively utilize on-node hardware acceleration. Overset assembly algorithms which use hardware acceleration are presented based on successful accelerated algorithms in real-time ray tracing and computational geometry. Timing results for core overset assembly operations are presented showing a maximum O(100x) speedup when using hardware acceleration. A novel method for turbulent fluid flow is presented which utilizes over-decomposition of the flow domain to produce task-parallelism allowing asynchronous calculation of the different steps of the method while also providing overlap between data transfer and computation. A mixed precision solver is utilized which provides a balance between optimal performance and numerical accuracy. A cost effective and accurate artificial compressibility pressure regularization is used which has minimal memory complexity and minimizes computational cost while maintaining accuracy. A primal-dual Laplacian operator is introduced which produces accurate results on skewed meshes. Results for canonical flow cases with overset meshes are shown illustrating the method's accuracy and numerical properties. Substantial speed-up is demonstrated for the numerical method reaching upwards of 50 times as fast as the non-accelerated method for high cell loadings.

A variational flexible multibody formulation for partitioned fluid–structure interaction: Application to bat-inspired drones and unmanned air-vehicles

We present a three-dimensional (3D) partitioned aeroelastic formulation for a flexible multibody system interacting with incompressible turbulent fluid flow. While the incompressible Navier–Stokes system is discretized using a stabilized Petrov–Galerkin procedure, the multibody structural system consists of a generic interaction of multiple components such as rigid body, beams and flexible thin shells along with various types of joints and connections among them. A co-rotational framework is utilized for the category of small strain problems where the displacement of the body is decomposed into a rigid body rotation and a small strain component. This assumption simplifies the structural equations and allows for the incorporation of multiple bodies (rigid as well as flexible) in the system. The displacement and rotation constraints at the joints are imposed by a Lagrange multiplier method. The equilibrium conditions at the fluid–structure interface are satisfied by the transfer of tractions and structural displacements via the radial basis function approach, a scattered data interpolation technique, which is globally conservative. For the coupled stability in low structure-to-fluid mass ratio regimes, a nonlinear iterative force correction scheme is employed in the partitioned staggered predictor–corrector scheme. The convergence and generality of the radial basis function mapping are analyzed by carrying out systematic error analysis of the transfer of fluid traction across the non-matching fluid–structure interface where a third-order of convergence is observed. The proposed aeroelastic framework is then validated by considering a flow across a flexible pitching plate configuration with serration at the trailing edge. Finally, we demonstrate the flow across a flexible flapping wing of a bat modeling the bone fingers as beams and the flexible membrane as thin shells in the multibody system along with the joints.

Automatic generators of multi-patch B-spline meshes of blade cascades and their comparison

In this paper, we propose several approaches for automatic construction of planar multi-patch B-spline parameterizations around one or between two consecutive blade profiles in a blade cascade starting from given design parameters (blade cascade is obtained by unfolding a cylindrical cross-section of the runner), which have been implemented in C++ as fully automatic generators and are an integral part of our in-house automatic shape optimization tool for water turbines. These B-spline parameterizations have to be prepared for the definition of periodic boundary conditions on the corresponding parts of the boundary, which makes finding of analysis-suitable multi-patch B-spline parameterizations even more challenging. All approaches are compared with respect to the selected geometric quality measures and also with respect to the results from our in-house isogeometric incompressible turbulent fluid flow solver and we discuss pros and cons of these approaches.

Radial profile of dissipation rate for turbulent flow of incompressible fluid in round direct pipe based on generalized local balance model

The article is focused on the problem of generalized local balance turbulence model. Generalized local balance turbulence model is considered. The one-parameter turbulence model is based on semi-empirical dissipation rate transport equation with negative coefficient of diffusion. To determine a coefficient of this equation, Laplace’s method of asymptotic estimation of a double integral is used. To compute radial dissipation profile the turbulence model is applied to the pipe flow. The known wall and axial functions are used as boundary conditions. The turbulence model is applied to the pipe flow to compute radial dissipation profile, well-known wall and axial functions are used as boundary conditions. Comparisons with known experimental data are given.

Longitudinal Flow of Curviline Rotation Deflector by Viscous Incompressible Liquid

The article considers longitudinal axisymmetric flow of curved rotation deflector with an averaged turbulent flow of incompressible fluid. Based on the Bernoulli equation, they determined the thickness of the water film descending from the deflector. They proved that the film thickness depends on the hydraulic resistance of the deflector. The jet departure range (deflector radius) was determined.

On numerical simulation of flexibly supported airfoil in interaction with incompressible fluid flow using laminar–turbulence transition model

In this paper the problem of mutual interaction of the incompressible turbulent fluid flow with a flexibly supported airfoil is addressed. The problem is mathematically described with the aid of the Reynolds averaged Navier–Stokes equations. The turbulence is modeled with the aid of k-kL-ω transition model. In order to treat the motion of the domain the system of equations are written in the arbitrary Lagrangian–Eulerian. The structure motion is governed by a nonlinear system of ordinary differential equations, where two degrees of freedom for the rotation and the vertical translation are used. The problem is numerically discretized with the aid of the finite volume method using the linear reconstruction technique. The numerical results are shown.

Assessment and verification of mean effective diameter of internal channels fabricated by laser powder bed fusion

Channels with small diameters, used for example in conformal cooling, can nowadays be fabricated by laser powder bed fusion. Measurements of the mean effective diameter and surface topography are important to quantify the flow capabilities through the channel. In this paper, a new method using X-ray computed tomography is developed to obtain the mean effective diameter and mean surface topography height. The developed method is verified by determining the mean effective diameter using incompressible turbulent fluid flow simulations, whereupon the determined mean surface topography height is fed as an input to the simulation. The method is proved to offer a non-destructive and relatively fast approach to measure the mean effective diameter and mean surface topography height in circular channels.

Extending the Meshless Local Petrov–Galerkin Method to Solve Stabilized Turbulent Fluid Flow Problems

The aim of this paper is to extend the meshless local Petrov–Galerkin method to solve stabilized turbulent fluid flow problems. For the unsteady incompressible turbulent fluid flow problems, the Spalart–Allmaras model is used to stabilize the governing equations, and the meshless local Petrov–Galerkin method is extended based on the vorticity-stream function to solve the turbulent flow problems. In this study, the moving least squares scheme interpolates the field variables. The proposed method solves three standard test cases of the turbulent flow over a flat plate, turbulent flow through a channel, and turbulent flow over a backward-facing step for evaluation of the method’s capability, accuracy, and validity purposes. Based on the comparison of the three test cases results with those of the experimental and conventional numerical works available in the literature, the proposed method shows to be accurate and quite implemental. The new extended method in this study together with the previously published works of the authors (on extending the meshless local Petrov–Galerkin method to solve laminar flow problems) now, for the first time, empower the meshless method to solve both laminar and turbulent flow problems.

A 3D common-refinement method for non-matching meshes in partitioned variational fluid–structure analysis

We present a three-dimensional (3D) common-refinement method for non-matching unstructured meshes between non-overlapping subdomains of incompressible turbulent fluid flow and nonlinear hyperelastic structure. The fluid flow is discretized using a stabilized Petrov–Galerkin method, and the large deformation structural formulation relies on a continuous Galerkin finite element method. An arbitrary Lagrangian–Eulerian formulation with a nonlinear iterative force correction (NIFC) coupling is achieved in a staggered partitioned manner by means of fully decoupled implicit procedures for the fluid and solid discretizations. To begin, we first investigate the accuracy of common-refinement method (CRM) to satisfy the traction equilibrium condition along the fluid-elastic interface with non-matching meshes. We systematically assess the accuracy of CRM against the matching grid solution by varying grid mismatch between the fluid and solid meshes over a tubular elastic body. We demonstrate the second-order accuracy of CRM through uniform refinements of fluid and solid meshes along the interface. We then extend the error analysis to transient data transfer across non-matching meshes between the fluid and solid solvers. We show that the common-refinement discretization across non-matching fluid–structure grids yields accurate transfer of the physical quantities across the fluid–solid interface. We next solve a 3D fluid–structure interaction (FSI) problem of a cantilevered hyperelastic plate behind a circular bluff body and verify the accuracy of coupled solutions with respect to the available solution in the literature. By varying the solid interface resolution, we generate various non-matching grid ratios and quantify the accuracy of CRM for the nonlinear structure interacting with a laminar flow. We illustrate that the CRM with the partitioned NIFC treatment is stable for low solid-to-fluid density ratio and non-matching meshes for the 3D FSI problem. Finally, we demonstrate the 3D parallel implementation of the common-refinement with the NIFC method for a realistic engineering problem of drilling riser undergoing complex vortex-induced vibration with strong added mass effects and turbulent wake flow.

Isogeometric analysis for turbulent flow

The article is devoted to the simulation of viscous incompressible turbulent fluid flow based on solving the Reynolds averaged Navier–Stokes (RANS) equations with different k−ω models. The isogeometrical approach is used for the discretization based on the Galerkin method. Primary goal of using isogeometric analysis is to be always geometrically exact, independent of the discretization, and to avoid a time-consuming generation of meshes of computational domains. For higher Reynolds numbers, we use stabilization SUPG technique in equations for k and ω. The solutions are compared with the standard benchmark example of turbulent flow over a backward facing step.

Couette Longitudinal Turbulent Flow Between Coaxial Cylinders

Within the framework of the model of anisotropic wall turbulence, an analytical solution is obtained for the problem on turbulent incompressible-fluid flow between two coaxial circular cylinders due to the motion of the internal cylinder along the common axis (Couette flow). The velocity profile and the surface-friction coefficient of the internal cylinder are determined. The solution is compared to the existing solutions and to experimental data.

A comparative study of turbulence models performance for separating flow in a planar asymmetric diffuser

This paper presents a computational study of the separated flow in a planar asymmetric diffuser. The steady RANS equations for turbulent incompressible fluid flow and six turbulence closures are used in the present study. The commercial software code, FLUENT 6.3.26, was used for solving the set of governing equations using various turbulence models. Five of the used turbulence models are available directly in the code while the v 2– f turbulence model was implemented via user defined scalars (UDS) and user defined functions (UDF). A series of computational analysis is performed to assess the performance of turbulence models at different grid density. The results show that the standard k– ω, SST k– ω and v 2– f models clearly performed better than other models when an adverse pressure gradient was present. The RSM model shows an acceptable agreement with the velocity and turbulent kinetic energy profiles but it failed to predict the location of separation and attachment points. The standard k– ε and the low-Re k– ε delivered very poor results.

LARGE EDDY SIMULATION OF TURBULENT INCOMPRESSIBLE FLUID FLOWS BY A NINE-NODES CONTROL VOLUME-FINITE ELEMENT METHOD

The main purpose of this work is the numerical computation of turbulent incompressible fluid flows by a nine-node control volume finite element method (CVFEM) using the methodology of large-eddy simulation.. The domain is discretized using nine nodes finite elements and the equations are integrated into control volumes around the nodes of the finite elements. The Navier?Stokes equations are filtered for simulation of the large scales variables and the sub-grid scales stress appearing due to the filtering process are modeled through the eddy viscosity model of Smagorinsky. The two-dimensional benchmark problem of the lid-driven cavity flow is solved to validate the numerical code and preliminary results for the horizontal and vertical velocity profiles at the centerlines of the cavity and the stream functions are presented and compared with available results from the literature.

LARGE EDDY SIMULATION OF TURBULENT INCOMPRESSIBLE FLUID FLOWS BY A NINE-NODES CONTROL VOLUME-FINITE ELEMENT METHOD

The main purpose of this work is the numerical computation of turbulent incompressible fluid flows by a nine-node control volume finite element method (CVFEM) using the methodology of large-eddy simulation.. The domain is discretized using nine nodes finite elements and the equations are integrated into control volumes around the nodes of the finite elements. The Navier?Stokes equations are filtered for simulation of the large scales variables and the sub-grid scales stress appearing due to the filtering process are modeled through the eddy viscosity model of Smagorinsky. The two-dimensional benchmark problem of the lid-driven cavity flow is solved to validate the numerical code and preliminary results for the horizontal and vertical velocity profiles at the centerlines of the cavity and the stream functions are presented and compared with available results from the literature.

Dynamics of Particles Advected by Fast Rotating Turbulent Fluid Flow: Fluctuations and Large-Scale Structures

Dynamics of particles advected by fast rotating incompressible turbulent fluid flow is studied. Fast rotation and particle inertia imply the divergent particle velocity field and result in both intermittency in spatial distribution of particles and formation of the large-scale inhomogeneous structures. A nonzero mean helicity of fluid flow causes an additional mean nondiffusive turbulent flux of inertial particles. Intermittency in the systems with and without external pumping is studied. Fast rotation causes anomalous scaling already in the second moment of inertial particle number density and may result in excitation of a small-scale instability of inertial particle distribution, which leads to the formation of small-scale particle clusters. We discuss the relevance of our results for atmospheric, astrophysical, and industrial turbulent rotating flows. [S0031-9007(98)07241-X]

Self-Excitation of Fluctuations of Inertial Particle Concentration in Turbulent Fluid Flow.

A mechanism for intermittency in spatial distribution of small inertial particles advected by a turbulent incompressible fluid flow is discussed. The mechanism is related to self-excitation (i.e., exponential growth without an external source) of fluctuations of concentration of small particles in a turbulent fluid flow. The effect is caused by the inertia of particles which results in a divergent velocity field of particles. An equation for the high-order correlation functions of concentration of small inertial particles is derived. It is shown that the growth rates of the higher moments of particle concentration are higher than those of the lower moments, i.e., particle spatial distribution is intermittent. Similar phenomena occur for noninertial admixtures advected by divergent turbulent velocity field.

Turbulent thermal diffusion of small inertial particles.

A new physical effect, turbulent thermal diffusion, is discussed. This phenomenon is related to the dynamics of small inertial particles in incompressible turbulent fluid flow. At large Reynolds and Peclet numbers the turbulent thermal diffusion is much stronger than the molecular thermal diffusion. It is shown that inertia of particles under certain conditions can cause a large-scale instability of spatial distribution of particles. Inertial particles are concentrated in the vicinity of the minimum (or maximum) of the mean temperature of the surrounding fluid depending on the ratio of material particle density to that of the surrounding fluid.