This paper reports the processes by which a single-phase 3-D CFD model of hydrodynamics in a 17-km-long dam reservoir was developed, verified and tested. A simplified VOF model of flow was elaborated to determine the effect of wind on hydrodynamics in the lake. A hexahedral mesh with over 17 million elements and a k-ω SST turbulence model were defined for single-phase simulations in steady-state conditions. The model was verified on the basis of the extensive flow measurements (StreamPro ADCP, USA). Excellent agreement (average error of less than 10%) between computed and measured velocity profiles was found. The simulation results proved a strong effect of wind on hydrodynamics in the lake, especially on the development of the water circulation pattern in the lacustrine zone.
Nowadays we can commonly encounter with revitalizations of an original HPPs which were earlier fitted with Francis turbines. They were often placed to the locations with low head and higher discharge, which means high specific speed (ns > 400). Generally it is quite complex to design Francis turbines for such high specific speed. These very old turbines usually have lower efficiency due to the earlier limited possibilities of hydraulic design. An exchange of a water turbine with another type can be quite expensive and therefore it can be more suitable to change only an old runner for a new one. In this article the design process of high specific speed turbine ns = 430 is described. Optimization was done as the full-automatic cycle and was based on a simplex optimization method as well as on a genetic algorithm. For the parameterization of the runner blade, the BladeGen software was used and CFD (Computational Fluid Dynamics) analysis was run in Ansys CFX v.14 software. The final shape runner blade was reached after computing about 1000 variants, which lasted about 250 computational hours. and Obsahuje seznam literatury
The problem of thermal fatigue in pipe connections under the influence of streams mixing is one of the most discussed problems on international conferences. Numerous failures occur in industry as a result of this damage mechanism. It is caused by frequent stress changes developed by an effect of non-stationary thermal fields. The degree of damage is greatly dependent on characteristic of material geometrical design of a pipe connection in operational conditions. The report is dealing with influence of temperature differences of mixing media streams upon pipe material damage cumulation. It is focused on a perpendicular T-junction made of ferritic steel, which is protected inside with an anticorrosive weld deposit from austenitic steel. Six cases of temperature differences will be considered for particular operational conditions with a step of 50 °C, and the damage cumulation process will be observed. Thanks to it, it will be possible to judge better the meaning of streams temperature differences. and Obsahuje seznam literatury
Validation of a numerical simulation using experimental data is a necessary prerequisite for verification of proper use of numerical method. This article deals with a comparison of velocities as predicted by an idealized model of human upper airways during stationary inspiration for three different breathing regimes. For the purpose of this study, a model which includes a realistic geometry of the mouth cavity and glottis coupled with and idealized geometry of the trachea and bronchial tree up to the fourth generation on branching was made. Calculations were compared with experimental data acquired by Phase-Doppler Particle Anemometry (P/DPA) on the identical geometry. Velocity data were compared at three points in the trachea. Specific air flow characteristics are documented and discussed based on results of the numerical simulation of the velocity field. and Obsahuje seznam literatury
The paper presents three-dimensional CFD analysis of two-phase (sand-water) slurry flows through 263 mm diameter pipe in horizontal orientation for mixture velocity range of 3.5-4.7 m/s and efflux concentration range of 9.95- 34% with three particle sizes viz. 0.165 mm, 0.29 mm and 0.55 mm with density 2650 kg/m3 . RNG k-ε turbulence closure equations with Eulerian multi-phase model is used to simulate various slurry flows. The simulated values of local solid concentration are compared with the experimental data and are found to be in good agreement for all particle sizes. Effects of particle size on various slurry flow parameters such as pressure drop, solid phase velocity distribution, friction factor, granular pressure, turbulent viscosity, turbulent kinetic energy and its dissipation have been analyzed.
The paper deals with the design of stator channels of the aerator using CFD code ANSYS Fluent. The main problem is to design proper inclination of the channels corresponding with the direction of flow at the impeller outlet. The direction of flow is variable along the channel and represented by the absolute velocity angle. Therefore, this angle is computed first, and according to it, the inclination of stator channels is designed. Numerical simulations are made as single-phase flow for two different shapes of channels and for two different channel incllnations - for already computed ones and for ones used in older type of aerator which this work develops. Stator channels inclined by computed angle that corresponded with the direction of flow had the best results. On the other hand, the channels inclined by the same angle as the channels of older aerator had the worst efficiency. The decrease of aerator efficiency was caused by the large vortexes in the stator channels. and Obsahuje seznam literatury a názvosloví
This work with numerical and experimental studies of specific issues of natural convection flow around a horizontal cylinder in a space limited by rectangular cavity. Physical models of laminar unsteady flows have been used for numerical calculations of heat transfer coefficients of four different diameters of horizontal cylinders and for several temperature gradients. Procedures and results of the experimental studies are contained in the next section. All results were compared with different authors and different approaches, However the Nusselt numbers can be estimated due to the temperature interval, the results indicate need for further investigation. and Obsahuje seznam literatury
Flow of particles suspended in a fluid can be found in numerous industrial processes utilizing sedimentation, fluidization and lubricated transport such as food processing, catalytic processing, slurries, coating, paper manufacturing, particle injection molding and filter operation. The ability to understand rheology effects of particulate flows is elementary for the design, operation and efficiency of the underlying processes. Despite the fact that particle technology is widely used, it is still an enormous experimental challenge to determine the correct parameters for the process employed. In this paper we present \mbox{2-dimensional} numerical results for the behavior of a particle based suspension and compare it with analytically results obtained for the Stokes-flow around a single particle.
This study deals with the numerical solution of a 2D unsteady flow of a compressible viscous fluid in a channel for low inlet airflow velocity. The unsteadiness of the flow is caused by a prescribed periodic motion of a part of the channel wall with large amplitudes, nearly closing the channel during oscillations. The channel is a simplified model of the glottal space in the human vocal tract and the flow can represent a model of airflow coming from the trachea, through the glottal region with periodically vibrating vocal folds to the human vocal tract.
The flow is described by the system of Navier-Stokes equations for laminar flows. The numerical solution is implemented using the finite volume method (FVM) and the predictor-corrector MacCormack scheme with Jameson artificial viscosity using a grid of quadrilateral cells. Due to the motion of the grid, the basic system of conservation laws is considered in the Arbitary Lagrangian-Eulerian (ALE) form.
The authors present the numerical simulations of flow fields in the channel acquired from a program developed exclusively for this purpose. The numerical results for unsteady flows in the channel are presented for inlet Mach number M∞ = 0.012, Reynolds number Re∞ = 5x103 and the wall motion frequency 100 Hz. and Obsahuje seznam literatury
The aim of this paper is to show the complex thermal analyses used to design of aircraft electronic control unit. Control Power Supply for Jet (CPSJ). The goal is to examine thermal conditions of power and control electronics components. With respect to aircraft application a computational fluid dynamics (CFD) method is used for heat transfer coefficient determination. This method is compared to analytic solution based on Petuchov equation of Nusselt number. The temperature conditions inside the CPSI unit are presented as results. and Obsahuje seznam literatury