Band 1, Heft 4

A novel manufacturing approach similar to filament winding has been developed and automated and is able to produce the Composite Material Marine Current Turbines (CMMCT), which have significant advantages over traditional designs. This paper presents numerical results to investigate the performance of these turbines. The numerical approach was performed using Computational Fluid Dynamics (CFD) in a free stream of water with various hydrodynamic flow conditions. Static torque, extracted power and power coefficient were calculated at different rotating speeds in a free stream with various hydrodynamics flow conditions. The power coefficient of CMMCT was compared to that of traditional current turbines. The calculated results will provide a fundamental understanding of the impeller as a water turbine, and this design method is used to shorten the design process and improve the water turbine’s performance.

Computational fluid dynamics (CFD) is an important tool for development of microfluidic systems based on gasliquid two-phase flow. The formation of Taylor slugs at microchannel T-junctions has been studied both experimentally and numerically, however discrepancies still exist because of difficulties in correctly representing experimental conditions and uncertainties in the physics controlling slug flow, such as contact line and velocity slip. In this paper detailed methods and results are described for the study of Santos and Kawaji [1] on the comparison of experimental results and numerical modeling. The system studied consisted of a rectangular microchannel Tjunction nominally 100 μm in hydraulic diameter, used to generate Taylor slugs from air-water perpendicular flow. The effect of flow rates on parameters such as slug length, velocity slip, void fraction and two-phase frictional pressure drop were studied. Numerical simulation was performed using FLUENT volume-of-fluid (VOF) model. It is proposed in this paper that this microfluidic problem be taken up by researchers in the field as a benchmark case to test other numeric codes in comparison to FLUENT on the prediction of micro-scale multiphase flow, and also to model in more detail the experimental system described to obtain greater accuracy in prediction of microfluidic slug formation.

Acoustic resonances are frequently fatal problems in centrifugal pump operations. Low pressure pulsation of fluid in the blade pass frequency is helpful to prevent from such problems. In addition, for a high quality centrifugal pump, a lower broadband noise level is also on demand. The acoustic resonance and broadband noise are associated with unsteadiness of flow in the pump. Even there exist extensive analyses of unsteady flow in centrifugal pumps by means of CFD so far, the effect of high viscosity of fluid pumped on the unsteadiness of flow feature remains unclear. Thus, the unsteady flow in an experimental centrifugal pump was exploited numerically when it transported the liquids with different viscosities. The velocity profiles at the impeller discharge were validated with the results of LDV measurement for water. The viscosity effect on the fluctuation of flow in the volute was clarified quantitatively. It was shown the increasing viscosity of fluid makes the fluctuation in flow variables less substantial and results into a less noticed tendency of separation of flow from the blade pressure side.

A three-dimensional (3D) computational fluid dynamic simulation of a vortex tube is carried out to examine its flow and thermal characteristics. The aim of this work is to model the performance of the vortex tube and to capture the highly swirling compressible flow behavior inside the tube for an understanding of the well known temperature separation process. Simulations were carried out using the standard k-ɛ, k-omega, RNG k-ɛ and swirl RNG k-ɛk-ɛ turbulence models. An experimental setup was built and tested to validate the simulation results. The RNG k-ɛ turbulence model yielded better agreement between the numerical predictions and experimental data. This model captured well the essential features of the flow including formation of the outer vortex and the inner reverse vortex flow. Flow and geometric parameters that affect the flow behavior and energy separation are studied numerically. Effects of the inlet pressure, with and without an insert in the tube, are examined by numerical experiments.

In this paper, we performed a comparison of four turbulence models using for numerical simulation of the hydrodynamic structure generated by a Rushton turbine in a cylindrical tank. The finite volume method was employed to solve the Navier-Stokes equations governing the transport of momentum. In this study four closure models tested were: k-ɛ standard, k-ɛ RNG, k-ɛ Realizable and RSM (Reynolds Stress Model). MRF (Multi Reference Frame) technique was used with FLUENT software package. The present work aimed to provide improved predictions of turbulent flow in a stirred vessel and in particular to assess the ability to predict the dissipation rate of turbulent kinetic energy (e) that constitutes a most stringent test of prediction capability due to the small scales at which dissipation takes place. The amplitude of local and overall dissipation rate is shown to be strongly dependent on the choice of turbulence model. The numerical predictions were compared with literature results for comparable configurations and with experimental data obtained using Particle Image Velocimetry (PIV). A very good agreement was found with regards to turbulence.

In this paper, a new computational benchmark test for fluid dynamics is presented. The new benchmark is based on the interaction of a single vortex structure (vortex patch) with a wall. It will be shown that it is possible to distinguish two critical or threshold values of the Reynolds number in the considered flow. The increase of the Reynolds number causes the appearance of the vortex bubble in the near-wall region first, and then next, the eruption of the boundary layer phenomenon. Further increase of the Reynolds number causes the flow to be more complex. The eruption phenomenon becomes more intense and also shows its regenerative nature.

The aim of this paper is to study the effect of baffles length on the turbulent flows in stirred tanks. The hydrodynamic behaviour induced by a Rushton turbine (RT6) is numerically predicted by solving the Navier-Stokes equations in conjunction with the Renormalization Group (RNG) of the k-ɛ turbulence model. These equations are solved by a control volume discretization method. The numerical results from the application of the computational fluid dynamics (CFD) code Fluent with the multi-reference frame (MRF) model are presented in the vertical and horizontal planes in the impeller stream region. Our studies were carried out on three different systems. The most effective system was selected based on its calculated power consumption figure. All numerical results showed good agreement with experimental data.

In this paper, the mixing performance of double helical ribbons and double helical screw ribbons impellers mounted on stirred tanks is numerical investigated. The computer simulations are conducted within a specific computational fluid dynamic (CFD) code, based on resolution of the Naviers-Stokes equations in the laminar flow with a finite volume discretization. The field velocity and the viscous dissipation rate are presented in different vessel planes. The global characteristics and the power consumption of these impellers are also studied. The numerical results showed that the velocity field is more active with the double helical screw ribbons impeller. In this case, the effectiveness of the viscous dissipation and the pumping flow has been obviously noted. Also, the pumping and the energy efficiency reach the highest values at the same Reynolds number. The good agreement between the numerical results and the experimental data quietly confirmed the analysed method.

Aerodynamic characteristics of a vehicle are important elements in its design and construction. A low drag coefficient brings significant fuel savings and increased engine power efficiency. In designing and developing vehicles trough computer simulation process to determine the vehicles aerodynamic characteristics are using dedicated CFD (Computer Fluid Dynamics) software packages. However, the results obtained by this faster and cheaper method, are validated by experiments in wind tunnels tests, which are expensive and were complex testing equipment are used in relatively high costs. Therefore, the emergence and development of new low-cost testing methods to validate CFD simulation results would bring great economic benefits for auto vehicles prototyping process. This paper presents the initial development process of a Formula SAE Student race-car prototype using CFD simulation and also present a measurement system based on low-cost sensors through which CFD simulation results were experimentally validated. CFD software package used for simulation was Solid Works with the FloXpress add-on and experimental measurement system was built using four piezoresistive force sensors FlexiForce type.

The paper deals with a CFD based study of the transverse permeability of a textile woven structure. The reported numerical investigation is preconditioned by both previous experimental and CFD study on jet systems. It is also based on detailed experimental investigation of the porous structure of single layer woven fabrics, made of staple fiber yarns. The flow in through-thickness direction of the woven structures is presented as jet systems, issuing from set of orifices. Two different types of jet system (3×3 jets and 5×5 jets) with two types of jet cross sections (square and circular), corresponding to two different woven structures, are simulated. An analysis is made in terms of the structure of the woven fabrics (area and shape of the interstices between the threads), the parameters of the flow passing through the textile (velocity profiles and velocity fields through isosurfaces), the role of the type of the jet systems, representing the flow and the influence of the shape of the interstices between the threads on the flow pattern. It was found that the applied approach could be effectively used for studying of the transverse permeability of the woven fabrics.