CFX Computational Fluid Dynamics Research Articles

CFD APPROACH TO ANALYSIS OF THE FLOW CHARACTERISTICS OF A HIGH-PRESSURE FRANCIS TURBINE

With the growth of computational mechanics, the virtual hydraulic machines are becoming more and more realistic to get minor details of the flow, which are not possible in model testing. In present work, 3D turbulent real flow analyses in hydraulic Francis turbine have been carried out at three guide vane opening and different rotation speed using Ansys CFX computational fluid dynamics (CFD) software. The average values of flow parameters like velocities and flow angles at the inlet and outlet of runner, guide vane and stay vane of turbine are computed to derive flow characteristics. To improve the energy performance at the preliminary design stage of the turbine, numerical flow simulations should be carried out. This CFD approach reduces costs and time in comparison with the experimental approach and makes it possible to improve and analyze turbine performance and its design before the model is manufactured. The computational complex of programs provides an opportunity to see the picture of pressure distribution, the field of velocity vectors and the movement of fluid particles for substantiation and analysis of results. The results of the computational study confirm that the hydraulic efficiency of a hydraulic turbine largely depends on the losses in the guide vane and the runner, which means it is these elements that should be given the most attention, their design and coordination of the flow in them. Analysis of the energy loss in the flow part of the Francis turbine was carried out using programs for calculating fluid flow in two-dimensional and three-dimensional formulation. The obtained calculated data correspond to the previously known experimental recommendations for high-pressure Francis turbine. The issues of increasing the energy performance of a projected high-pressure Francis turbine were considered.

Effect of Recess Shape on the Performance of a High-Speed Hybrid Journal Bearing

Hybrid bearings are getting more and more attention because of their ability to provide both hydrodynamic support for high-speed rotors and hydrostatic lift in low-speed conditions such as during startup. Hybrid bearings are typically designed with recess grooves to modify the pressure profile and as a result to enable the lift capacity of the bearing under various operating conditions. The literature has shown that the size and shape of the recesses have not been systematically and quantitatively studied in detail. The goal of this study is to build a 3D analytical model for a hybrid-recessed bearing with five pockets and provide a comprehensive analysis for the effect of recess geometry on the overall performance of the bearing. In this study, a baseline model selected from the literature is constructed and validated using the ANSYS cfx computational fluid dynamics software package. A sensitivity analysis of the design variables on the performance of the bearing has been performed using design expert software. The length, width, and depth of the recess as well as the diameter and location of the five inlet ports have been selected as design variables. A multivariable and multi-objective genetic algorithm has also been solved using isight software with the goal of optimizing the geometry of the recess to maximize load capacity while minimizing bearing power loss from friction torque. The results of the baseline model show reasonable agreement with the experimental data published in the literature. The regression models for lift force and friction torque were both found to be statistically significant and accurate. It has been shown that friction torque decreases as the length of recess in the circumferential direction increases. The results showed that the load capacity is highly correlated to the diameter of the orifice, d. These results provide a deeper understanding of the relationship between the shape of the recess and bearing performance and are expected to be useful in practical hybrid-bearing design.

COMPUTATIONAL FLUID DYNAMICS INVESTIGATION ON THE OUTER WING OF FLYING BOAT REMOTE CONTROL MODEL

The experiment of Wing in Surface Effect craft A2B and A2C B type for (1 - 2) seaters prototype are the background of this research. The aerodynamic, hydrodynamic, thrust and weight data of these prototypes were already investigated. The best ratio of Thrust per Weight is around 0.4 from this experience to fulfill the liftoff condition from the water surface. The step position on the hull as the theoretical prediction of Wing in Surface Effect craft is made (2 to 10)0 from center of gravity, c.g location to the step position. These formulas have been used to designing the Flying Boat remote control model. The whole process to build the remote control model is shown on this paper. The investigation of the outer wing of Flying Boat remote control model had been done to elaborate the aerodynamic and hydrodynamic characteristic. Included the laser photo camera tracking to 3 D model and Computational Fluid Dynamics analysis have been done also. The three dimensions (3 D) figures are evaluated by CATIA software and then these data results were transfer to the input of CFx Computational Fluid Dynamics (CFD) software. The meshing, pressure distribution and forces distributions during hydro planing of outer wing and pontoon of Flying Boat remote control model have been analyzed by CFx Computational Fluid Dynamics software. The Z force on the outer wing and pontoon showed a good result.

Evaluation and Reduction of Elevated Height Printing Defects

Ink jet printing at elevated heights is known to initiate unsteady laminar flows which lead to imaging defects often referred to as wood-grain or fogging. An investigation of the unsteady flow development was conducted using both experimental and numerical simulation techniques. High speed imaging revealed that the interaction between the air flow induced from droplet drag and the couette flow entrained from the substrate motion develops large eddies which roll along the droplet stream and lead to unsteady flows causing wood-grain defects. ANSYS CFX computational fluid dynamics (CFD) simulations are presented to support the experimental results and to provide a higher degree of understanding of the flow dynamics. Several techniques are revealed which illustrate how wood-grain defects can be improved. These techniques strive to enable ink jet technologies to be used in a wider range of applications with large height variations or which require jetting at elevated heights to prevent contact with print heads.In addition to unsteady flow defects, two other phenomenons related to elevated height printing were included in this study: (1) excessive nozzle plate wetting and (2) excessive drag on droplets ejected into a still flow field.

Low-Reynolds-Number Aerodynamic Performances of the NACA 0012 and Selig–Donovan 7003 Airfoils

A comparative study of two airfoils at low Reynolds numbers using the transitional unsteady Reynolds-averaged Navier–Stokes shear-stress transport model and the ANSYS CFX computational fluid dynamics suite is proposed. The NACA 0012 and Selig–Donovan 7003 airfoils were selected and exposed to chord-based Reynolds numbers ranging from to at angles of attack ranging from 0 to 8 deg. The adopted numerical model and setup were shown to accurately predict the main flow features. Specifically, both laminar separation without reattachment and laminar-separation-bubble flow modes were observed depending on the airfoil geometry and orientation, Reynolds number, and freestream-turbulence intensity. In general, with increasing angle of attack or Reynolds number, laminar-separation bubbles shrank and receded toward the leading edge while vortex-shedding periodicity and coherency degraded. In all cases, the Selig–Donovan 7003 proved of superior aerodynamic performance when compared to the NACA 0012, which was expected.

CFD validation of performance improvement of a 500 kW Francis turbine

Conventionally assessing of turbine performance was done by conducting model experiments which at times become costly and time consuming for several design alternatives in design optimization. Recently, computational fluid dynamics (CFD) has become a more cost effective tool for predicting detailed flow information in turbine space to enable the selection of the best design. With the growth of computational mechanics, the virtual hydraulic machines are becoming more and more realistic to get minor details of the flow, which are not possible in model testing. The inverse design technique and fully 3-dimensional flow simulations were performed early to manufacture the newly developed runner. It allows a quick and efficient improvement and optimization of turbine components. The system has been applied to the optimization of a Francis turbine runner for a turbine replacement project. In present work, 3D turbulent real flow analyses in hydraulic Francis turbine have been carried out at four guide vane opening at constant rotational speed using Ansys CFX computational fluid dynamics (CFD) software. The newly developed runner from reverse engineering and CFD results show an enhanced performance. The average values of flow parameters like velocities and flow angles at the inlet and outlet of runner, guide vane and stay vane of turbine are computed to derive flow characteristics. The aim was to analyze the flow behavior and pressure distribution to further fine-tune the whole numerical experiment to achieve the level of accuracy necessary for the concept design of a revitalized turbine. The obtained results are in good agreement with the in site experiments, especially for the characteristic curve.

Numerical simulations of LNG vapor dispersion in Brayton Fire Training Field tests with ANSYS CFX

Federal safety regulations require the use of validated consequence models to determine the vapor cloud dispersion exclusion zones for accidental liquefied natural gas (LNG) releases. One tool that is being developed in industry for exclusion zone determination and LNG vapor dispersion modeling is computational fluid dynamics (CFD). This paper uses the ANSYS CFX CFD code to model LNG vapor dispersion in the atmosphere. Discussed are important parameters that are essential inputs to the ANSYS CFX simulations, including the atmospheric conditions, LNG evaporation rate and pool area, turbulence in the source term, ground surface temperature and roughness height, and effects of obstacles. A sensitivity analysis was conducted to illustrate uncertainties in the simulation results arising from the mesh size and source term turbulence intensity. In addition, a set of medium-scale LNG spill tests were performed at the Brayton Fire Training Field to collect data for validating the ANSYS CFX prediction results. A comparison of test data with simulation results demonstrated that CFX was able to describe the dense gas behavior of LNG vapor cloud, and its prediction results of downwind gas concentrations close to ground level were in approximate agreement with the test data.

Research with Cfx Software on Frame Mould Temperature Field Simulation in Autoclave Process

For autoclave technology in large complex structure manufacturing of composite materials, temperature distribution is the most important factor in process control. Previous researchers have mainly focused on composite exothermic curing reaction and exterior temperature coupling. For the exterior temperature field (especially mould temperature field), a simplified approach of uniformity was also conventionally adopted in those researches. Actually, moulds commonly utilised in autoclave processes have a frame structure and their temperature field variation is a combined heat transfer mechanism involving solid heat conduction, air heat conduction and forced convection. Hence in any phase of an autoclave process, the mould temperature field is non-uniform in the spatial domain. This non-uniform distribution of mould temperature has an important impact on the curing degree distribution and leads to residual stress. In this work, using ANSYS CFX computational fluid dynamics (CFD) software, simulation methodology for frame mould temperature field in autoclave process has been established, and its effectiveness has been verified experimentally. On this basis, a series of frame mould simulation examples has been developed and the impact of mould design parameters on the temperature field was achieved. The results will be of value in frame mould design and manufacturing defect control of composite structures.

Analysis of source term aspects in the experiment Phebus FPT1 with the MELCOR and CFX codes

Several aspects related to the source term in the Phebus FPT1 experiment have been analyzed with the help of MELCOR 1.8.5 and CFX 5.7 codes. Integral aspects covering circuit thermalhydraulics, fission product and structural material release, vapours and aerosol retention in the circuit and containment were studied with MELCOR, and the strong and weak points after comparison to experimental results are stated. Then, sensitivity calculations dealing with chemical speciation upon release, vertical line aerosol deposition and steam generator aerosol deposition were performed. Finally, detailed calculations concerning aerosol deposition in the steam generator tube are presented. They were obtained by means of an in-house code application, named COCOA, as well as with CFX computational fluid dynamics code, in which several models for aerosol deposition were implemented and tested, while the models themselves are discussed.

Numerical Simulations of Non-Isothermal Flow in Off-Axis Rotation of a Can Containing a Headspace Bubble

This paper describes numerical simulations of the non-isothermal, laminar flow of Newtonian and non-Newtonian liquids inside rotating cylindrical cans containing a headspace air bubble. Two modes of rotation are considered: axial rotation about a horizontal axis and end-over-end rotation. The rotational speed is held constant so that once initial transients have decayed the flow field in both cases is periodic. The aim of the numerical simulations, carried out using the ANSYS CFX computational fluid dynamics software, is to compare liquid heating times for different flow conditions. To reduce computational run times the calculations are carried out for a liquid with an artificially high value of thermal diffusivity. For axial rotation the simulations have been carried out using 2D and 3D models and it is shown that a 2D model can identify trends in heating times. In both end-over-end and axial modes, rotational speeds and radii of rotation are identified which minimize the heating time. The conditions are shown to correspond closely to those which maximize a measure of mixing in previous studies of isothermal flow.