| This work was financially supported by the National Natural Science Foundation of china key project "Water-electro-mechanical coupling studies of hydropower station (50839003)" and other National Natural Science Foundation of china projects (number:50079007,90210005,50579025,51279071) long-term funded. The theoretical model of weakly compressible coupling water hammer and cavitation were established based on related theories about weakly compressible fluid. A non-diagonally dominant nonlinear massively parallel computing solver was developed based on the proposed theoretical model for the weakly compressible problem. Completed a coupling water hammer field test for a high head, long pipeline hydropower station and get a lot of measured data about coupling water hammer. Based on tens of thousands of self-developed code, we completed a series of fine numerical simulation about the problem of coupling water hammer for a high head hydropower station shaft penstock and the problem of cavitation flow in high head and low head Francis turbine. The results were compared with the literature and test measured in good agreement. It proves the correctness of theories, methods and source code in this thesis. Some innovative research has been made. Research work mainly in the following four areas:1. Theoretical modeling(1) According to the relevant weakly compressible fluid theory, established equations suitable for describing weakly compressible water in hydropower penstock. It can describe the hydraulic transients of water hammer wave for wave-fluid coupling, wave-wave coupling.(2) On the basis of classic penstock shell model, instead the potential flow theory traditionally with a three-dimensional viscous fluid. In any curvilinear coordinates, based on the ALE framework the shell model control equations of weakly compressible water were created. The water hammer model of the wave-fluid coupling, wave-wave coupling, fluid-structure interaction for the penstock and hydroturbine was obtained.(3) The weakly compressible water single phase cavitation model and mass transport cavitation model was created. It can describe the cavitation of weakly compressible water for a hydroturbine under transient conditions.2. Programming(1) Use OpenFoam C++class library, wrote tens of thousands of program code, a non-diagonally dominant nonlinear massively parallel computing solver was developed based on the proposed theoretical model for the hydroturbin weakly compressible and cavitation.(2) Implemented coupling the finite element module in OpenFoam extended version and self-developed weakly compressible CFD code. Precision interpolation method was completed. It enables the attributes of finite volume cell center of description fluid spatial dispersion interpolated to node. According to contact surface condition, the displacement and force transfer is implemented.(3) A program code was developed for coupled weakly compressible water with penstock movement. It combines the weakly compressible water source CFD code and FEAP finite element shell element code. Based on orthogonal curvilinear coordinates shell element was completed in FEAP. Meanwhile, the k-ε turbulence model in OpenFoam class library was called by using object-oriented technology. This code takes into account both the weak compressibility of water and fluid turbulence characteristics.3. Prototype test studyCombined with theoretical study, took two years to complete coupling water hammer prototype observation and test analysis for a high head, long pipeline hydropower. A large number of measured data was obtained. The first-hand data about weak compressibility of water and coupling water hammer characteristics after the load rejection were obtained too. It verifies the theoretical model and program code is correct.4. Numerical simulation and validation(1) Based on weakly compressible coupling water hammer theory, cavitation models and solver crated in this thesis, numerical simulation of the Netherlands DELFT water hammer benchmark test device A was completed. Numerical results clearly shows that the coupling water hammer fluctuation including:wave-flow, waves-waves and flow-structure coupled in test device. Calculations and test measured data fully consistent.(2) Using the solver developed in this thesis, a fluid structure interation analysis to be completed for the above tests high head, long pipeline hydropower shaft of penstock segment. The pressure and the stress were calculated at the penstock elbow on tow case. The result of wall strain and stress agree with the test measured data.(3) Using the cavitation model proposed and program code developed in this thesis, simulated a NACA0015hydrofoil widely used in the literature, and compared the calculation results with the test and calculated data by literature provided. The results show that the results calculated by the proposed model and the developed code in this thesis accord with the cavitation test results by literature. It can clearly capture the cavity quasi-periodic motion law for hydrofoil leading edge the growth of the sheet cavity, the reentrant jet breaking the cavity, rear cloud cavitation shedding while a new sheet cavity is growing.(4) A numerical simulation of cavitation was implemented for full flow channel of a high and a low head Francis turbine with the proposed model and the code respectively. The cavitation characteristics were analyzed for spiral casing-vanes, guide vanes, runner and draft tube. The draft tube vortex shape, the cavitation characteristics and pressure pulsation for runner and draft tube cone segment are identical with an actual operation hydroturbin unit.(5) With program code developed in this thesis, a numerical simulation of cavitating turbulent flow in a Francis turbine with draft tube natural air admission was completed. It takes into account the phase change for water-gas-vapor multiphase flow. The pressure pulsation was analyzed after air into the draft tube. The calculated results coincide with the actual operation.Through the above four aspects of the work, In this thesis, for the problem about hydroturbin weakly compressible water coupling water hammer and cavitation, from theoretical modeling, computational methods, source code development, hydropower water hammer test prototype observations, hydroturbine cavitation flow simulation and other aspects, the theoretical research and related technology development was completed systematically. Research work took nearly10years, has made innovative achievements. |
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