Simulation Of Three-dimensional Turbulent Flow Research Articles

Numerical simulation of three-dimensional turbulent flows based on the mathematical model of wave processes

Numerical simulation of three-dimensional turbulent flows based on the mathematical model of wave processes

3D MODELING OF TURBULENT FLOWS USING LES AND RANS APPROACHES BASED ON FILTERED EXPEDITION DATA

The article describes the developed software that made it possible to process a large amount of data from observations of the movement and parameters of the aquatic environment in the Sea of Azov, which was obtained during expeditionary research using the ADCP hydrophysical probe, using the filtration procedure. The filtering procedure significantly reduces the spread of data and the amplitude of fluctuations, which, in turn, makes it possible to more adequately evaluate the information obtained during field experiments. For different filter widths, a box filter, a Gauss filter and a Fourier filter were used. In these calculations, the filter width was set based on the size of the hydrodynamics problem to be solved and the grid scale corresponding to this size. The obtained data are planned to be used for numerical simulation of three-dimensional turbulent flows using the LES approach and comparison with the results of averaging by RANS.

Turbulent flow simulations of the common research model on Cartesian grids using recursive fitting approach

In this study, we propose a new method that uses the recursive fitting method and wall function for the three-dimensional turbulent flow simulation. The recursive fitting method based on the Cartesian grid method is employed for the automatic generation around two- and three-dimensional geometries. The grid approximately represents the concave and convex features, i.e., a wing–fuselage juncture and wing trailing edges. The wall boundary conditions can be imposed on the wall faces; thus, the conservation laws are strictly satisfied. Meanwhile, using the wall function allows turbulent boundary layers to be accurately reproduced. The turbulent flow simulation using the wall function is straightforward because the flow variables at the first cell centroid are employed for friction velocity estimation. However, the distance between the body surface and the first cell centroid varies since cells with different shapes are generated. Therefore, the simulation using the proposed method is validated through turbulent flow simulations in two dimensions. The results show the accurate predictions of the turbulent boundary layers. To investigate the capacity of the proposed method, three-dimensional simulation around aircraft at a transonic cruise condition is conducted. The automatically generated grids by the proposed method approximately represent the geometric features. The results of flow simulation show that the surface pressure and skin friction coefficient distributions agree with those of the reference simulation on a conventional body-fitted grid. Further, predicted pressure and viscous drag coefficients are reasonable compared with those of the reference simulation.

3D turbulent currents simulation in the coastal zone using the LES approach based on filtered ADCP data

The interest in turbulence in shallow waters, such as the Azov Sea, is caused by the fact that in the places of its existence there is an intensive transfer of the amount of motion and heat, the spread of passive impurities, the transfer of suspended particles. These processes significantly affect the formation and spatial structure of physical, chemical and biological fields of reservoirs and their spatial and temporal changes. Depending on the smoothing scale of the series of initial readings of the flow meters, the pulsation characteristics of the flow velocity were determined, which were processed in order to obtain data on turbulence and its scales. The research results provided empirical data on the conditions of generation and existence of small-scale turbulence. The collected empirical material is currently being processed to study the internal structure of the recorded disturbances of small-scale turbulence. In this paper, small-scale motion is excluded from the Navier-Stokes equations by applying the filtration operation and is modeled using subgrid models. To do this, in two-dimensional and three-dimensional cases, various types of filters are used: a box filter, a Gaussian filter and a Fourier filter, with a gradual decrease in the filter width, which allows you to reproduce a wider frequency range of fluctuations of the solution. The obtained data are planned to be used for numerical simulation of three-dimensional turbulent flows using the LES approach and comparison with the results of averaging by RANS. The article considers the possibilities of using various types of approximations for parametrization of vertical turbulent exchange. Algebraic models for calculating the coefficient of vertical turbulent exchange and semi-empirical turbulence models are compared.

ФИЛЬТРАЦИЯ НАТУРНЫХ ДАННЫХ ДЛЯ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ ТРЕХМЕРНЫХ ТУРБУЛЕНТНЫХ ТЕЧЕНИЙ С ПРИМЕНЕНИЕМ ПОДХОДА LES

Turbulence and subsequent mixing are important mechanisms which determine the dynamics of the coastal zone, as well as the transfer of momentum, mass and heat. In this paper, smallscale motion is excluded from the Navier–Stokes equations by applying the filtering operation. It is then modeled using subgrid models. In two-dimensional and three-dimensional cases, various types of filters are used: a box filter, a Gaussian filter and a Fourier filter, with a gradual decrease in the filter width. This enables the reproduction of a wider frequency range of fluctuations of the solution. The natural data obtained during the expedition in the Central-Eastern part of the Sea of Azov and in the Taganrog Bay at the research vessel Deneb of the Southern Scientific Center of the Russian Academy of Sciences were subjected to the filtration procedure. The hydrophysical ADCP probe Workhorse Sentinel 600 was used to measure the three-dimensional velocity vector of the water medium. In this way more than 3,000,000 initial measurements were obtained, at each of the 17 stations more than 150,000 were taken. The data thus obtained will be used for the digital simulation of three-dimensional turbulent flows using the LES approach and comparison with the results of averaging by RANS.

Optimisation of Pelton turbine jet deflector using CFD analysis

The high head Pelton turbines operate with extreme conditions. In case to need a sudden stop of operation, one of the important parts is jet deflector, which can be in push-out, or cut-of options. The paper presents the optimisation procedure of Pelton Turbine push-out jet deflector shape using numerical simulation of three-dimensional turbulent flow in order to minimize the forces, stresses, deformations and torque of jet deflector servomotor. The calculations are performed using the CFD package Ansys CFX. The steps for flow modelling, 3-D geometry definition, mesh generation, pre-processing and post-processing, as well as the optimised results obtained from the numerical simulation of the flow in the jet-deflector are presented. The work corresponds with the actual approach of methods development for flow simulation and calculations of Pelton Turbines. The kinematic and dynamic flow parameters are calculated based on CFD simulations. The results of the calculations represents reliable tool in the procedure of development and construction of Pelton Turbines parts.

Vortex Cascade Features of Turbulent Flow in Hydro-Turbine Blade Passage with Complex Geometry

A large-eddy simulation of three-dimensional turbulent flow for a hydro-turbine in the transitional process of decreasing load from rated power to no-load has been implemented by using ANSYS-Fluent in this paper. The survival space occupied by different scale flow structures for the different guide vane opening degrees was well captured. The flow characteristics in the transitional process were obtained. Different forms of the channel vortex were studied. The features of the vortex cascade and dissipation of the turbulent energy in blade passage were analyzed. The results show that the scales of the vortex structures have a large change in the transitional process of rejecting load, and the vortex distributions in the blade passage are significantly distinguished. The survival space of the different scale eddies in the blade passage is closely related to the scales of the vortex. The survival volume ratio of the adjacent scale vortex in the runner is about 1.2–1.6. The turbulent kinetic energy and eddy viscosity increase rapidly along the blade passage with the small-scale eddies going up, which implies that a dissipating path for the energy in the blade passage is formed.

Investigation on the fluctuation of hydraulic exciting force on a pump-turbine runner during the load rejection process

The flow-induced vibration is one of the important reasons causing the instability of pump-turbines during the load rejection process. However, the flow mechanism is not clear. In this study, the load rejection process of a pump-turbine was investigated, considering the clearance between the runner and stationary parts, through three-dimensional turbulent flow simulation with the dynamic mesh technology. Unsteady pressure boundary conditions were established at the inlet of the spiral-casing and outlet of the draft tube. The rotational speed of runner was calculated through coupling the rigid body motion with the water flow. The simulated rotational speed of runner shows a good consistency with the corresponding experimental data. Based on the numerical results, the fluctuation of the hydraulic thrust and hydraulic torque on the runner and their formation mechanism were analysed. The results show that there exists complex flow in the draft tube and in the vaneless space during the load rejection process. The complex flow leads to the severe fluctuation of hydraulic thrust and hydraulic torque on the runner with a low frequency, which is about 0.06∼0.4 times rated rotational frequency of the runner. Consequently, the hydraulic exciting source may induce intense vibration of the runner potentially.

Numerical Simulation of Flow and Heat Transfer in Rotating Cooling Passage With Turning Vane in Hub Region

Numerical simulation of three-dimensional turbulent flow and heat transfer was performed in a multipass rectangular (AR = 2:1) rotating cooling channel with and without turning vane in the hub region under various flow conditions, with two different Reynolds numbers of 10,000 and 25,000, two different channel orientations of 45-deg and 90-deg, and the rotation number varies from 0 to 0.2. This study shows that the addition of the turning vane in the hub turn region does not cause much impact to the flow before the hub. However, it significantly alters the flow reattachment and vortex distribution in the hub turn region and after the hub turn portion. The local heat transfer is deeply influenced by this complex flow field and this turning vane effect lasts from the hub turn region to the portion after it.

Effect of collision and velocity model of lattice Boltzmann model on three-dimensional turbulent flow simulation

ABSTRACTVarious collision and velocity models of the lattice Boltzmann model (LBM) were compared to determine their effects on the efficiency of a three-dimensional homogeneous isotropic decaying turbulent flow simulation. We determined that a decrease in the number of velocities, in particular, 13-velocities, which can be used in the quasi-equilibrium lattice Boltzmann and in the multiple-relaxation time models (MRT), could considerably decrease the computational effort. However, decreasing the number of velocities deteriorates the stability and the accuracy of the results. By comparing the collision models, we also determined that the stability of the entropic lattice Boltzmann model (ELBM), and 19- and 27- velocity MRT is much higher than in other models. However, the numerical viscosity introduced by the ELBM underestimates the enstrophy, and the computational effort increases because of the calculation overhead required to solve the additional equations if special care is not given to the calculation.

Critical rotating speed of rotor cup in an air suction open-end spinning machine

Simulation of three-dimensional turbulent flow in a rotor spinning machine is carried out, and the flow structure and behavior in the rotor cup are analyzed. The governing equations are the steady three-dimensional Navier–Stokes equations and the Spalart–Allmaras turbulence model. The results show that the rotating speed has great influence on the flow behavior in the rotor cup. It is found that there is a critical speed of the rotor cup beyond which the pressure and velocity on the slip surface is not changed anymore regardless of the magnitude of the rotating speed. When the rotating speed is larger than this critical speed, the flow structure becomes unstable with the increasing of the rotating speed. The mechanism of this phenomenon is that the airflow in the rotor groove passes about 180 degrees from two sides along the rotor wall and a pressure balance is achieved. When the rotating speed is larger than the critical speed, the balance will break down. When the rotor speed is low, the flow characteristic in the air-inlet plane is mainly determined by the high-speed airflow at the outlet of the transfer channel. However, when the rotor speed is higher than the critical speed of n = 80,000 r/min, the flow behavior is mainly determined by the rotating rotor. In the meridian plane perpendicular to the air-inlet plane, the flow behavior is mainly determined by the rotor speed. The rotating speed of the rotor has little effect on the flow characteristics in the transfer channel.

Assessment of spanwise domain size effect on the transitional flow past an airfoil

In most large-eddy and direct numerical simulations of flow past an isolated airfoil, the flow is assumed periodic in the spanwise direction. The size of the spanwise domain is an important geometrical parameter determining whether the turbulent flow is fully developed, and whether the separation and transition patterns are accurately modeled. In the present study, we investigate the incompressible flow past an isolated NACA0012 airfoil at the angle of attack of 5 degrees and Reynolds number 5 × 104. The spanwise domain size Lz, represented by the aspect ratio AR = Lz/C where C is the airfoil chord length, is varied in the range 0.1−0.8. The effect of varying the normalized spanwise domain size AR is examined via direct numerical simulation (DNS) on several aspects of the turbulent flow quantities including the time-averaged and time-dependent behavior as well as the spanwise variation of the selected statistical quantities. DNS results reveal that different aspect ratios result in close predictions of the time-averaged aerodynamic quantities, and the velocity field except for a slight difference in the separation bubble. Smaller aspect ratios tend to underpredict the turbulent fluctuations near the separation point but overpredict them inside the separation bubble. Large differences are observed for multiple statistical quantities near the reattachment point, especially the turbulent kinetic energy budget terms. The leading edge separation is notably three-dimensional for simulation at AR = 0.8, while remaining quasi-2D for smaller aspect ratios. The spanwise two-point correlation coefficient shows significant dependence on the position of the probe and the velocity component analyzed: small aspect ratios do not produce uncorrelated results for all the velocity components. The simulation results demonstrate that examining only a few statistical quantities may result in a misleading conclusion regarding the sufficiency of the spanwise domain size. Reliable metrics to establish the sufficiency of spanwise domain size require thorough analysis of the turbulent statistics, and are necessary for three-dimensional simulation of turbulent flow in similar configurations.

Three-dimensional simulation of turbulent flow in a membrane tube filled with semi-circular baffles

As qualitative and quantitative properties of fluid dynamics in baffle-filled channels can be obtained through computational fluid dynamics (CFD) simulations, the effects of types of baffles on flow patterns, behavior and features can be fully understand. In this research, a three-dimensional (3D) simulation method based on CFD was applied for fluid flow in membrane tubes in which semi-circular baffles were inserted. In addition, the effects of flow geometric parameters on turbulent flow in a membrane tube equipped with semi-circular baffles were studied, and parameters involving pitch to baffle diameter ratio (L/D=1, 2 and 3) and baffle orientation angle (β=90° and 180°) were considered. According to the obtained results from 3D simulation, it was found that the fluid average velocity, shear stress and mass transfer on the tube wall increased by further extension of the baffle angles from 90° to 180°. Subsequently, the filtration performance in these types of tubes was significantly improved by this arrangement. In addition, the obtained results from the simulation were in good agreement with the experimental data in a cross-flow micro-filtration process of calcium carbonate suspensions.

Comment on “Numerics of the lattice Boltzmann method: Effects of collision models on the lattice Boltzmann simulations”

Critical comments on the entropic lattice Boltzmann equation (ELBE), by Li-Shi Luo, Wei Liao, Xingwang Chen, Yan Peng, and Wei Zhang in Ref. , are based on simulations, which make use of a model that, despite being referred to as the ELBE by the authors, is in fact equivalent to the standard lattice Bhatnagar-Gross-Krook equation for low Mach number simulations. In this Comment, a concise review of the ELBE is provided and illustrated by means of a three-dimensional turbulent flow simulation, which highlights the subgrid features of the ELBE.

A novel shaft-less double suction mini pump

A novel double suction shaft-less mini pump was developed for heat control of small energy systems in this study. The mini pump impeller with an exit diameter of 40 mm was combined with the motor rotor supported by the hybrid dynamic bearing. The specific speed of the pump was 125 min−1 m3 min−1 m. The hydraulic performance of the pump was investigated experiment- tally under four rotational speeds. From the test results, it was recognized that the pump could provide a flow discharge of 5 L/min and head of 1.5 m, which are applicable for the heat control system of a 3 kW fuel cell. A three-dimensional turbulent flow simulation in the pump was also conducted near the design point. The numerical results showed that the average hydraulic performance of the mini pump was predicted reasonably. From the internal flow simulation, it was revealed that the favorable inflow condition upstream of impeller inlet could be attained by applying the double suction shaft-less design for the mini pump.

Numerical simulation of three-dimensional turbulent flow in multistage axial compressor blade row

Numerical simulation of three-dimensional turbulent flow in a multistage axial compressor blade row is conducted. A high resolution, third-order ENN scheme is adopted to catch the shockwave and simulate the turbulent flow correctly, while an LU-SGS implicit method is chosen to improve computation rate. A detailed and highly efficient numerical simulation system is thus constructed. The investigation is focused on the grid connecting methods between the rotor and the stator and the corresponding treatment of rotor-stator interactional surface. The final results of a three-stage axial compressor with inlet guide vanes conform well to the experimental data.

Large-Eddy simulation of three-dimensional turbulent flow around a circular pier *

In this article, the turbulent flow field and the scouring mechanism around a circular pier were numerically investigated using the Large Eddy Simulation (LES) method for three scouring holes. The effects of the bottom topographies on the flow structure were studied in detail. The results show that at the downstream of the pier, as the scouring depth increases, the bed shear stress decreases and approaches to the undisturbed shear stress, however, the turbulent intensity, the fluctuating pressure, and the vertical pressure gradient increase gradually.

Large eddy simulation of three-dimensional turbulent flows by the finite element method

The main objectives of this work are the formulation, implementation and applications of a numerical algorithm to simulate turbulent, incompressible, isothermal flows. The transient three-dimensional flow is analyzed using an explicit Taylor-Galerkin scheme and the finite element method with hexahedrical eight-node element. Turbulence is simulated using Large Eddy Simulation. For sub-grid scales two models were implemented, the classical Smagorinsky's model and the dynamic eddy viscosity model. For the second filtration, which is necessary in the dynamic model, a new method was developed based on independent finite elements that involve each node in the original mesh. The implemented scheme is efficient and good results with low additional computational cost were obtained. Results for two classical problems, the driven cavity and the backward facing step are presented. Comments about the model applicability for flows with high Reynolds numbers are also presented.

그리드 컴퓨팅을 이용한 열유동 해석 기법에 관한 기초 연구

Simulation of three-dimensional turbulent flow with LES and DNS lakes much time and expense with currently available computing resources and requires big computing resources especially for high Reynolds number. The emerging alternative to provide the required computing power and working environment is the Grid computing technology. We developed the CFD code which carries out the parallel computing under the Grid environment. We constructed the Grid environment by connecting different PC-cluster systems located at two different institutes of Pusan National University in Busan and KISTI in Daejeon. The specification of PC-cluster located at two different institutes is not uniform. We run our parallelized computer code under the Grid environment and compared its performance with that obtained using the homogeneous computing environment. When we run our code under the Grid environment, the communication time between different computer nodes takes much larger time than the real computation time. Thus the Grid computing requires the highly fast network speed.

Simulation of Three-Dimensional Turbulent Flows around an Ahmed Body-Evaluation of Finite Differencing Schemes-

The Reynolds-averaged Navier-Stokes equations with the equations of the k-.epsilon. turbulence model are solved numerically in a general curvilinear system for a three-dimensional turbulent flow around an Ahmed body. The simulation is especially aimed at the evaluation of three finite differencing schemes for the convection term, which include the upwind differencing scheme(UDS), the second order upwind differencing scheme(SOU scheme) and the QUICK scheme. The drag coefficient, the velocity and pressure fields are found to be changed considerably with the adopted finite differencing schemes. It is clearly demonstrated that the large difference between computation and experiment in the drag coefficient is due to relatively high predicted values of pressure drag from both front part and vertical rear end base. The results also show that the simulation with the QUICK or SOU scheme predicts fairly well the flow field and gives more accurate drag coefficient than other finite differencing scheme.