Smoothed Particle Hydrodynamic of Hydraulic Jumps in Spillways

Abstract: This thesis focus on the complex natural phenomena of hydraulic jumps using the numerical method Smoothed Particle Hydrodynamics (SPH). A hydraulic jump is highly turbulent and associated with turbulent energy dissipation, air entrainment, surface waves and spray and strong dissipative processes. It can be found not only in natural streams and in engineered open channels, but also in your kitchen sink at home. The dissipative features are utilized in hydropower spillways and stilling basins to reduce high velocity flows. Potentially, such flow can cause erosion and reduce the lifetime and increase maintenance costs of spillways and related structures which must be avoided. Usually, spillways are engaged to safely pass extreme flooding events and redirect the flow during maintenance shutdown of the production units, i.e. turbines and generators. It is hence vital to understand and be able to predict the involved processes in a hydraulic jump. The Lagrangian, meshless particle based numerical method SPH has been considered as the main computational method throughout this thesis. The ability of the SPH method to capture complex free-surfaces with large deformation and fragmentation, found in hydraulic jumps, makes it a strong modelling tool. However, the SPH method is less developed compared to the established Finite Volume- (FVM) and Finite Element (FEM) methods. Initially, focus was on reproducing the results of previous studies where the geometrical aspect of hydraulic jumps was the main consideration (Paper A). Several modelling parameters were re-evaluated using a dam-break test case in Paper B and later applied in Paper C. Paper C, focused not only on the geometrical aspect of the hydraulic jump but also on the internal flow field and its relation to the free-surface. Later in Paper D, a new strategy on how to perform SPH hydraulic jump simulations based on periodic open boundaries was developed. Finally, the method developed was applied in two separate studies. In Paper E, the SPH method was compared with experiments performed at Vattenfall Research & Development in ¨Alvkarleby, Sweden. The SPH model, comprised of a channel and a scaled spillway outlet chute, not only captured the jump position but also large scale flow features. The final Paper F, was a continuation of Paper C where the internal flow field and its dynamical relationship with the free surface was reinvestigated using the more sophisticated SPH model.