Narrow Results

We present a particle method for the simulation of three dimensional compressible hydrodynamics based on a hybrid Particle-Mesh discretization of the governing equations. The method is rooted on the regularization of particle locations as in remeshed Smoothed Particle Hydrodynamics (rSPH).

The rSPH method was recently introduced to remedy problems associated with the distortion of computational elements in SPH, by periodically re-initializing the particle positions and by using high order interpolation kernels.

In the PMH formulation, the particles solely handle the convective part of the compressible Euler equations. The particle quantities are then interpolated onto a mesh, where the pressure terms are computed. PMH, like SPH, is free of the convection CFL condition while at the same time it is more efficient as derivatives are computed on a mesh rather than particle-particle interactions. PMH does not detract from the adaptive character of SPH and allows for control of its accuracy. We present simulations of a benchmark astrophysics problem demonstrating the capabilities of this approach.

This paper deals with numerical modeling of two-phase liquid jet breakup using the smoothed particle hydrodynamics (SPH) method. Simulation of multiphase flows involving fluids with a high-density ratio causes large pressure gradients at the interface and subsequently divergence of numerical solutions. A modified procedure extended by Monaghan and Rafiee is employed to stabilize the sharp interface between the fluids. Various test cases such as Rayleigh–Taylor instability, two-phase still water and air bubble rising in water have been conducted, by which the capability of accurately capturing the physics of multiphase flows is verified. The results of these simulations are in a good agreement with analytical and previous numerical solutions. Finally, the simulation of the breakup process of liquid jet into surrounding air is accomplished. The whole numerical solutions are accomplished for both Wendland and cubic spline kernel functions and Wendland kernel function gave more accurate results. Length of liquid breakup in Rayleigh regime is calculated for various flow conditions such as different Reynolds and Weber numbers. The results of breakup length demonstrate in satisfactory agreement with the experimental correlation. Finally, impinging distance and breakup length of a simple multijet setup are analyzed. The two-jet multijet has a longer breakup length than a three-jet one.

Application of Lagrangian meshless methods in modeling granular flow has been a major concern for researchers due to their particular nature. For modeling granular movement, it is assumed that the particles are continuous. The SPHysics code is developed for modeling the movement of Newtonian fluids in which the pressure is derived from the state equation. In this study, $\mu (I)$ and Herschel–Bulkley–Papanastasiou (HBP) viscoplastic models are implemented in the SPHysics code to analyze the movement of grains induced by the applied stresses. In the first model, the movement of granular particles is based on the characteristics such as inertia and friction coefficient, and in the second model, the movement is related to the non-Newtonian viscoplastic behavior of fluids. The accuracy of the models is evaluated by simulating the experimental benchmarks for granular dam break. The effect of length-to-height ratio on the failure mode of dam break phenomenon is also investigated. The performance of the models is increased by introducing the gate removal speed and also the harmonic mean of the viscosity instead of the viscosity proper to each particle. This study shows that the models could capture the behavior of grains in the static and the dynamic parts of the mass body.