جستجوی مقالات مرتبط با کلیدواژه « cfd » در نشریات گروه « آب و خاک »

The use of numerical methods is widely used in diagnosing the performance of hydraulic systems and optimizing them. Numerical modeling is less expensive than experimental work. Numerical methods can be used to check the accuracy of the results and compare them. In this thesis, the fluid volume method is used to simulate the free surface flow of water inside the lower discharger of Kani Sib Dam. Since the flow inside the dischargers is turbulent, k-ε, k-ε RNG, k-ω SST, k-ω and also LES turbulence models have been used and compared. Also, the discharge coefficient inside the lower discharger and the aeration flow have been investigated and compared.

To simulate the turbulent flow inside the lower discharger, continuity equations, momentum, energy and equation of state along with equations related to the aforementioned turbulence models have been solved using OpenFoam software.  The set of equations of conservation of mass, conservation of momentum and energy for turbulent flow, which are so-called Reynolds averaging equations, are the governing equations of the flow and are used to model the flow by solving them numerically.

The simulation and optimization of the hydraulic parameters of the turbulent flow in the lower dischargers of the Sib Mineral Dam has been completed using OpenFOAM. The results have been made on the parameters of the lower discharger of Sib mineral dam. And the optimization is done using genetic algorithm. In this research, it was found that with the increase of the hydraulic diameter, the discharge coefficient increases. Also, with the increase of the hydraulic diameter, the core of the water fluid jet inside the discharger undergoes a strong fluctuation, which can increase the shear stress. An excessive increase in shear stress can cause corrosion of the discharge walls. On the other hand, with a further decrease in shear stress, deposition inside the lower discharger increases. At the same time, with the increase in the length of the lower discharger, the discharge coefficient decreases. The optimal selection of the length of the lower drain depends on the height behind the dam. As the opening rate increases, the discharge coefficient also increases and the k- ε turbulence model gives more acceptable results to estimate the results. Finally, for each aeration flow rate, a set of optimal values for the discharge coefficient and the opening rate has been obtained.

Denil fishway contains a direct rectangular channel in different slope rates associated with special baffles inside the channel. The layout of the baffles provides an energy dissipation process which provides an acceptable operating condition for passing the fish in continues path along the channel. Denil fishway divides the current to two different parts, including the main current located at the middle of the channel and lateral currents along the frame position. The interaction between main and lateral currents provides the main process of mass and acceleration movement and concludes a significant energy reduction based on the turbulent process. In the other words, it can be concluded that the frequent baffles make the channel very rough, which results in a suitable condition for migrating fishes to the upstream (Cea et al., 2007). Rajaratnam and Katapodis (1983) conducted common research on the hydraulic of the fishway structures. They focused on the Denil fishway as one of the most important fishway structures among different types. The result of their study on the Denil fishway is the developed equation for measuring the discharge of the flow in the channel in various geometric scenarios. The physical model of the Denil fishway was constructed in the hydraulic laboratory at Alberta university, and the flow rate and velocity profiles were measured using the electromagnetic flowmeter and miniature velocimeter, respectively. Rajaratnam and Katapodis (1983) introduced six different Denil fishway types. The result of this study has shown that the output data are relatively similar to the Denil type 2. Equations (1), (2) are the main equations of the Denil fishway type 2 based on Rajaratnam and Katapodis (1983) studies.

Sudden expansion can be used as energy dissipater in the pressurized pipe flows. As the induced cavitation bubbles will cause large structural damage، estimating the amount of maximum developed under-atmospheric pressure (MDUAP) in sudden expansions is of particular interest. Pressure fluctuations، domain and intensity of cavitation depend on the amount of MDUAP. Therefore، estimating the amount of MDUAP is a vital task in the design stage. To carry out this study، various sudden expansions were developed by changing the geometry and flow properties. The developed sudden expansions were modeled using the CFD modeling technique. The obtained CFD based results were successful in analyzing the experimental observations. Therefore، the simulation model is capable of predicting the MDUAP under different conditions. In this paper، the M5P data mining model is used for the first time for establishing a fast، accurate، and cost-effective linkage between the geometry and flow properties of a sudden expansion and the amount of MDUAP. The results show that the developed M5P based simple rules can accurately predict the amount of MDUAP.