Hydrodynamic characteristics of lateral withdrawal with effects of the slope ratio

Lateral withdrawal is widely performed in water transfer and water supply projects. Hydrodynamic characteristics of intake are crucial to safe and stable operation. In this study, a 3-D numerical volume of fluid model was established and validated through experimental tests. Hydrodynamic characteristics and secondary flow were investigated under scenarios with the vertical slope and different slope ratios. The helix-shaped recirculation and surface vortex are generated, and the secondary flow near the surface layer is more serious. Adding a slope ratio is beneficial to improve the flow patterns and recirculation, while the surface vortex width increases. Additionally, with the decrease in the slope ratio, recirculation width and the ratio of recirculation to the width of the layer decrease, and the minimum values are 9.19 cm and 22.97%, respectively. However, the lower the slope ratio is, the greater recirculation inhibition affects are, and the more serious the surface vortex is. With the decrease in the slope ratio, the widest surface vortex width and the ratio of the widest surface vortex to the width of the layer increase from 6.1 to 12 cm and from 7.82 to 17.14%, respectively. This research represents an advance in lateral withdrawal and provides support for further designs.

Study on the Application of Particle Image Velocimetry with Resin and Rhodamine B as Alternative Seeding Particles in Pico Hydro Cross Flow Hydro Turbine

One of the solutions to overcome the lack of electricity problem in rural area is Crossflow pico-scale hydropower. In improving cross-flow turbine performance, understanding fluid phenomena is needed. Particle image velocimetry (PIV) measurement is one of the methods used to visualize the fluid flow phenomena inside the turbine. Expensive price of seeding particle leads to find the solution for this PIV method. The objective of this study is to use a cheap seeding particle from cheaper materials, mainly resin and rhodamine B. Besides that, in this study, PIV measurement is compared to 2D computational fluid dynamics (CFD) with multiphase volume of fluid model. From the results, several phenomenon can be observed at both of the methods (PIV and CFD) such as separation in the blade tip. Therefore, this study showed that an inexpensive material resin and rhodamine B as a seeding particle has a potential and ability to represent flow inside pico-hydro cross-flow turbine.

Hydrodynamic studies on liquid-liquid two phase flow separation in microchannel by computational fluid dynamic modelling

Microfluidic systems undergo rapid expansion of its application in different industries over the few decades as its surface tension-dominated property provides better mixing and improves mass transfer between two immiscible liquids. Synthesis of biodiesel via transesterification of vegetable oil and methanol in microfluidic systems by droplet flow requires separation of the products after the reaction occurred. The separation technique for multiphase fluid flow in the microfluidic system is different from the macro-system, as the gravitational force is overtaken by surface force. To understand these phenomena completely, a study on the hydrodynamic characteristics of two-phase oil-methanol system in microchannel was carried out. A multiphase Volume of Fluid model was developed to predict the fluid flow in the microchannel. An inline separator design was proposed along with its variable to obtain effective separation for the oil-methanol system. The separation performance was evaluated based on the amount of oil recovered and its purity. The capability of the developed model has been validated through a comparison of simulation results with published experiment. It was predicted that the purity of recovered oil was increased by more than 46% when the design with side openings arranged at both sides of the microchannel. The highest percentage recovery of oil from the mixture was simulated at 91.3% by adding the number of side openings to ensure the maximum recovery. The oil that was separated by the inline separator was predicted to be at 100% purity, which indicates that no methanol contamination throughout the separation process. The purity of the separated product can be increased by manipulating the pressure drop across the side openings. Hence, it can be concluded that the separation in a large diameter microchannel system is possible and methodology can be tuned to achieve the separation goal. Finally, the simulation results showed that the present volume of fluid model had a good agreement with the published experiment.

Analysis of a cylindrical cyclone separator used in aircraft turbine engine

Cyclone separators are components commonly used in the oil system of aircraft gas turbine engines to separate air from the oil. The major advantage of this component is simple construction and high reliability thus they do not require frequent inspections. The efficiency of the separator has a decisive impact on the quality of the oil, which directly cause a change in the efficiency of the oil system. Increased air content in the oil causes a pressure drop in the system and higher-pressure fluctuations, which in turn affect the proper lubrication of the engine components (bearings, gears). New engine designs require more compact separator designs to reduce weight and project costs while maintaining (and often increasing) their efficiency and reliability. To meet these requirements, it is necessary to use the flow modelling of the air-oil mixture in the design process to optimize the construction of the separator. The purpose of this paper is to present a numerical simulation approach using a volume of fluid model for aircraft turbine separator

Analysis of the Possibility of Using the Plain CFD Model to Simulate Two-Phase Flows in Spatial Systems of Pressure Sewer Networks

The paper analyzes the possibility of using the CFD (Computational Fluid Dynamics) method to predict the amount of sewage remaining in siphons after a full air blast of the pressure sewer system. For this purpose, the results from measurements carried out on a laboratory installation were compared with the results obtained from modelling using a spatial model (3D) and a plain model (2D) of the installation. To determine these models, the structure of the VOF (Volume of Fluid) model was used in the CFD method. The simulation calculations carried out make it possible to state that the use of the plain model with the development of the installation modelled in the plan does not result in significant deterioration of the obtained results. The possibility of using 2D models for modelling pumped sewer systems allows for a significant shortening of the calculation time, which, in practice, results in the possibility of modelling much larger and longer installations than is possible with 3D models.

Biphasic Computational Fluid Dynamics Modelling of the Mixture in an Agricultural Sprayer Tank

Agitation inside agricultural sprayer tanks can be studied while using an international standard procedure, based on obtaining internal samples of liquid. However, in practice, this test is not easy to perform. Herein, we propose the explicit study of the mixing procedure with biphasic computer simulations using Computational Fluid Dynamics (CFD). An experimental test was performed on a 3000 L tank of a commercial air-assisted sprayer, with two different agitation system configurations, in order to compare the results of several theoretical physical models of biphasic flows for CFD, both Eulerian and Lagrangian. From the analysis of these theoretical models, we conclude that the Volume of Fluid model is not viable and the Discrete Phase Model produces erroneous results, while the Eulerian and Mixture models can both be useful. However, the results obtained suggest that complex streams generated by real-world agitation systems produce more errors in calculations. Both models can be conducted in the design phase, prior to the implementation of the machine. In addition, the computer simulations allow for researchers to analyse the mixing process in detail, making it possible to evaluate the efficiency of an agitation system according to the time that is required to reach mixture homogeneity.

Investigation on the function of double tipping bucket for improvement of rainfall measurement

<p>The double-tipping bucket rain gauge (SL3-1) is widely used in meteorological stations to minimize the systematic errors by the influence of rainfall intensity on TBRs in China. With two tipping buckets, the upper tipping bucket turns over and injects rainwater into the converging funnel, and the lower tipping bucket can record the rainfall. In this study, CFD (computational fluid dynamic) simulations and experiments were performed to investigate the function of the double tipping bucket for TBRs in different rainfall intensity. In simulation, the volume-of-fluid model and Reynolds-averaged Navier–Stokes realizable k-ε model and dynamic mesh method were used. In experiments, electric balances, with accuracy of 0.001 g, were used to determine the water volume of the upper tipping bucket outflow. It shows that, with a converging funnel, natural precipitation is uniformed at a certain intensity around 1.9mm/min to control the rainwater outflow into blow tipping bucket to measure rainfall and reduce systematic errors caused by different precipitation intensities. Experimental results demonstrate that the outflow curve of the upper tipping bucket has high correspond with simulation results in tipping process. These results can provide knowledge of advantages of double tipping bucket rain gauge in rainfall measurement and improve the structure designs of double tipping bucket for TBRs and obtain more accurate rainfall data.</p>

Physical and numerical modeling of liquid slag entrainment in mould during slabs casting

The paper presents results of physical and numerical modeling of liquid slag entrainment during continuous casting of steel slabs process. The main aim of this work was to determine the critical casting speed and also to specify, which entrainment mechanism is most responsible for transport of slag droplets into steel volume. Physical modeling was based on water-oil model of mould, made on reduced linear scale of Sl = 0.4. In mathematical modeling, Realizable k-ε and LES WALE models were used to describe turbulent motion of water and oil, whereas Volume of Fluid model was used to take into account interactions between phases. It was found, that the main cause of slag entrainment is the formation of von Karman vortex in the vicinity of submerged entry nozzle. The results of laboratory experiments and numerical simulations were compared each other. Both method are a useful tools for modeling of slag entrainment. Great agreement was found between laboratory experiments and numerical simulation carried out using LES WALE model, regarding the shape of the oil and oil entrainment as a result of vortex structures formation. However, in the simulation case using Realizable k-ε model, the oil entrainment hasn’t been modeled for the conditions under consideration.