Predicting the Powering Performance of Different Vessel Types using an Open-Source CFD Propulsion Framework

CFD is a useful tool for ship designers looking for accurate predictions of the fuel efficiency achieved by a certain combination of hull, propeller and Energy Saving Devices (ESDs). Such predictions are key to meeting ever-increasing demands for reductions in emissions. However, CFD simulations of propeller-hull interaction can be very costly in terms of computational effort due to the need to resolve the unsteady flow around the rotating propeller. A popular approach to alleviate this cost, that has seen much practical use in industry, is the use of body forces (momentum sources) to represent the rotating propeller. There are many ways to describe the body force distribution in the fluid for a certain propeller and there are many options for what flow solver to use. In a previous meeting of the Society, an open-source framework for easily creating coupled solvers using an arbitrary combination of models was presented. Here, one of these coupled solvers is used to predict the local flow behind the propeller, as well as integral coefficients indicating performance, of four different vessels: a bulk carrier fitted with an Energy Saving Device, a fast container ship, a tanker and a fully appended twin-screw navy destroyer. All simulations are compared to available experimental data. Conclusions are drawn based on the success of the coupled solver to predict the local flow behind the propeller for each individual hull and how this relates to the vessel type and the local stern geometry.

A SEMI-ANALYTIC EIGENVALUE EXTENSION TO THE DOPPLER SLAB ANALYTIC BENCHMARK1

Advancement in multiphysics simulation has motivated interest in availability of analytic and semi-analytic benchmark solutions. These solutions are sought because they can be used to assess the accuracy of complicated numerical schemes necessary to simulate coupled physics systems. While there exist analytic solutions for fixed-source problems, benchmark-quality eigenvalue solutions are of interest because eigenvalue problems more closely align with analyses undertaken with coupled solvers. This paper extends a fixed-source benchmark, the Doppler Slab benchmark, to the eigenvalue case. A novel solution for this benchmark is derived. Numerical implementation of the benchmark is demonstrated through verification of numerical computation of the power reactivity coefficient.

Coupled Solvers for Gas-Solids Flows

In recent years, the application of coupled solver techniques to solve the Navier-Stokes equations has become increasingly popular. The main reason for this, is the increased robustness originating from the implicit and global treatment of the pressure-velocity coupling. The drawback of a coupled solver are the increase in memory requirement and the increased complexity of implementation. However, fully coupled methods are reported to have an overall favorable computational cost when a suitable pre-conditioner and algorithm for solving the resulting set of linear equations are employed. In solving multi-phase flow problems, the coupled solver approach is even more advantageous than in single-phase, due to the presence of large source terms arising from the coupling of the phases. In this chapter, various strategies for the fully coupled approach are discussed. These strategies include employing artificial compressibility, applying physically consistent cell face interpolation, and applying momentum weighted cell face interpolation. The idea behind the strategies is outlined and their advantages and disadvantages are discussed. The treatment of source terms and volume fraction in coupled methods is also shown. Finally, a number of examples of implementations and calculations are presented.