Ebrahim Jahanbakhsh

Flow Simulation of Jet Deviation by Rotating Pelton Buckets Using Finite Volume Particle Method

The objective of the present paper is to perform numerical simulations of a high-speed water jet impinging on rotating Pelton buckets using the finite volume particle method (FVPM), which combines attractive features of smoothed particle hydrodynamics (SPH) and conventional grid-based finite volume. The particles resolution is first validated by a convergence study. Then, the FVPM results are validated with available measurements and volume of fluid (VOF) simulations. It is shown that the pressure field in the buckets inner wall is in good agreement with the experimental and numerical data and the evolution of the flow pattern matches the high-speed visualization.

FPM Simulations of a High-Speed Water Jet Validation with CFD and Experimental Results

The present chapter reports the development of finite particle method (FPM) in the framework of a high-speed water jet simulation. The FPM kernel is used to improve the consistency of standard SPH for non-uniform particle distribution. The time integration is performed with a modified Verlet scheme. At the end of each time step, a particle shifting method is applied to mitigate the particle clustering issue by restoring a uniform particle spacing. The influence of particle spacing and maximum CFL number are investigated in the case of a high-speed water jet impinging on a flat plate. The influence of the impinging angle is analyzed for three different angles: 90°, 60°, and 30°. The time history of the pressure coefficient is recorded on the flat plate to compare the FPM simulations with available measurements and grid-based CFD simulations. The validation of the results is based on the comparison of the averaged pressure coefficient profile as well as the comparison of the free-surface location for the three different impinging angles.

Flow simulation of a Pelton bucket using finite volume particle method

The objective of the present paper is to perform an accurate numerical simulation of the high-speed water jet impinging on a Pelton bucket. To reach this goal, the Finite Volume Particle Method (FVPM) is used to discretize the governing equations. FVPM is an arbitrary Lagrangian-Eulerian method, which combines attractive features of Smoothed Particle Hydrodynamics and conventional mesh-based Finite Volume Method. This method is able to satisfy free surface and no-slip wall boundary conditions precisely. The fluid flow is assumed weakly compressible and the wall boundary is represented by one layer of particles located on the bucket surface. In the present study, the simulations of the flow in a stationary bucket are investigated for three different impinging angles: 72°, 90° and 108°. The particles resolution is first validated by a convergence study. Then, the FVPM results are validated with available experimental data and conventional grid-based Volume Of Fluid simulations. It is shown that the wall pressure field is in good agreement with the experimental and numerical data. Finally, the torque evolution and water sheet location are presented for a simulation of five rotating Pelton buckets.

Impact erosion prediction using the finite volume particle method with improved constitutive models

Erosion damage in hydraulic turbines is a common problem caused by the high- velocity impact of small particles entrained in the fluid. In this investigation, the Finite Volume Particle Method is used to simulate the three-dimensional impact of rigid spherical particles on a metallic surface. Three different constitutive models are compared: the linear strain- hardening (L-H), Cowper-Symonds (C-S) and Johnson-Cook (J-C) models. They are assessed in terms of the predicted erosion rate and its dependence on impact angle and velocity, as compared to experimental data. It has been shown that a model accounting for strain rate is necessary, since the response of the material is significantly tougher at the very high strain rate regime caused by impacts. High sensitivity to the friction coefficient, which models the cutting wear mechanism, has been noticed. The J-C damage model also shows a high sensitivity to the parameter related to triaxiality, whose calibration appears to be scale-dependent, not exclusively material-determined. After calibration, the J-C model is capable of capturing the material’s erosion response to both impact velocity and angle, whereas both C-S and L-H fail.

Silt motion simulation using finite volume particle method

In this paper, we present a 3-D FVPM which features rectangular top-hat kernels. With this method, interaction vectors are computed exactly and efficiently. We introduce a new method to enforce the no-slip boundary condition. With this boundary enforcement, the interaction forces between fluid and wall are computed accurately. We employ the boundary force to predict the motion of rigid spherical silt particles inside the fluid. To validate the model, we simulate the 2-D sedimentation of a single particle in viscous fluid tank and compare results with benchmark data. The particle resolution is verified by convergence study. We also simulate the sedimentation of two particles exhibiting drafting, kissing and tumbling phenomena in 2-D and 3-D. We compare the results with other numerical solutions.