Numerical Investigation And Performance Prediction On 3D Complex Viscous Flows In Hydromachinery

To achieve high parameter, excellent performance and fine reliability is the developing orientation of modern hydromachinery. A steady and high efficiency flow field ensures not only that the hydromachinery is of high performance and good economical efficiency but also that it is of fine reliability. However the internal flow in hydromachinery is very complex and the hydrodynamic stability induced by turbulent fluctuation is the uppermost factor for the steady operating of the hydromachinery. In this thesis the numerical ivestigaton on three-dimensional flow fields in a single stage and single suction centrifugal pump and a Francis turbine were carried out respectively by using of CFD method. These studies mainly consist of the following aspects.Numerical simulations were carried out on the flow fields in hydromachinery respectively based on RSM, k-ε, RNG k-ε, k-ω SST various turbulence models and UDS, SUDS advection differencing schemes, and the turbulence model and the advection differencing scheme adapted to simulate the flow fields in hydromachinery were confirmed.The numerical results obtained show that the flow in the impeller and volute of centrifugal pump is periodically unsteady. Due to the interaction between impeller and volute the flow is characterised by pressure fluctuations which are strong at impeller outlet and at the vicinity of the tongue. And the reduced pressure fluctuations are spread to the diffuser and also are reflected to the impeller inlet. The unsteady pressure fluctuations are also one of the most important reasons to induce vibration and noise. Secondly, at off design conditions the radial force is come forth at the impeller outlet due to static pressure circumferential unsymmetrical distribution at the impeller outlet with spirality volute. At part flow condition the static pressure value always obtained an increment along with the wrap angle manify, and the static pressure reached its maximum at the inlet of the diffuser. The reverse is true at the over flow condition. Thirdly, the flow field is characteristic of the vortex flow in the volute, and the vortex flow takes on so complex evolving process which is creating, increasing and dissipating ever and agah. All these result in large flow loss in the volute. Finally, the transient head of the centrifugal pump is characterised by large amplitude of fluctuation due to the change of relative position between impeller and volute, and the amplitude of fluctuation decrease along with discharge drop.The numerical simulation of the influence of varying the impeller-volute radial gap on the flow field and performance of the centrifugal pump was carried out and results showed that the maxmum efficiency point is moved in low flow direction with the reducing of outlet diameter...