Application of Smoothed Particle Hydrodynamics (SPH) for Preliminary Hydraulic Design

Problems in Computational Fluid Dynamics (CFD) are generally solved by employing the conventional grid-based numerical methods such as Finite Volume Method, where grid is required as computational frame to provide spatial discretization for governing equations. However, when simulating some special problems with large distortions, moving material interfaces or free surfaces, these methods can encounter some difficulties.

In the last few years, particle-based meshfree of adaptive and pure Lagrangian nature have been employed with advantage on these kind of problems. Smoothed Particle Hydrodynamics (SPH) is a particle-based meshfree approach where the fluid domain is represented by a set of arbitrarily distributed particles. Each particle is the point where physical quantities (such as position, velocity, density, pressure) are computed as an interpolation of the values of the neighbouring particles.

One of the main problem of SPH application to solve real engineering problems is the excessively long computational runtimes for 3D problems. However, in many cases, a strong reduction of computational runtime is obtained with a 2D approach, useful enough especially for preliminary design of hydraulic structures.

This paper describes the practical application of a 2D SPH model (DualSPHysics) for preliminary hydraulic design of drop structures: weir and energy dissipator, flow through a gate with hydraulic jump formation and impact type energy dissipator (see Figure 1 to Figure 3). All these structures belong to “Sistema Riachuelo” project; a wastewater system currently (2018) in construction in Buenos Aires (design flow of 27m3/s).

This work includes: methodology for adapting real 3D world data to 2D modelling, sensitivity analysis to determine how the changes of SPH parameters (initial distance among particles, artificial viscosity and interaction fluid- boundary particles coefficients) affect hydraulic results.

The results obtained with 2D SPH modelling for a case (Flow through a gate with hydraulic jump formation) are compared among 3D simulation applying finite volume CFD. The differences are discussed, and a proper agreement for practical purposes is verified.

It is concluded that the SPH modelling can be properly applied to preliminary hydraulic design, being an alternative method for some cases compared to other CFD methods such as finite volumes. Practical relationships among SPH parameters and Manning coefficient of roughness are obtained (such relationships are very scarce in the SPH bibliography).