Title:	Scale resolved flow simulations in ship hydrodynamics
DNr:	NAISS 2023/5-434
Project Type:	NAISS Medium Compute
Principal Investigator:	Rickard Bensow <rickard.bensow@chalmers.se>
Affiliation:	Chalmers tekniska högskola
Duration:	2023-11-01 – 2024-11-01
Classification:	20303
Keywords:

Abstract

There are several complex problems in ship hydrodynamics that require detailed information on the flow field, thus necessitating the use of scale resolved modelling approaches. The large spatial scales of a ship or underwater body are however such that the complete problem can not always be treated. We will here primarily look at a few limited problems where advanced simulation methodologies are needed to advance the understanding. In some cases complete ships will be studied where the system perspective, in combination with high resolution or fidelity, is needed to understand the process The first concerns the flow over rough surfaces. Already a new built vessel has a somewhat rough surface as the hull paint can not be applied completely smoothly, and the problem gets worse as wear and fouling deteriorates the surface. Wall-modelled LES will be performed for a series of test cases for non-equilibrium boundary layers developed within an international working group on this topic. The objectives are both to jointly improve understanding of the flow development as well as develop better models for flow modelling over rough surfaces. The second concerns simulation of hydroacoustic characteristics of underwater bodies and their radiated sound. Canonical building block flows will be studied, both in terms of flow dynamics and scales as well as the radiated sound, primarily using resolved LES. The objectives are to develop guidelines for choice of simulation approaches, problem set-up, and mesh resolution requirements for these types of problems. A third concern relates to cavitation nuisance, such as hull pressure pulses and radiated noise. Here, the detailed cavity dynamics in a marine propulsion system needs to be resolved in the simulation and the transient pressure field on the ship structure and in the surrounding fluid is sampled and analysed. Demanding DES or WMLES are needed for the full ship configuration, resolving the internal structure of the developing cavities on the propeller blades as well as the trailing tip vortex cavitation. Within this context, also cavitation erosion is an area that demands high computational resources. Erosion concerns the material damage due to collapsing vapour cavities. To be able to assess the risk of damage, the finer scales of the cavities needs to be resolved and their history traced towards collapse. In some of these processes, also compressibility needs to be considered requiring very small time steps in water. A fourth one is related to the effect of the ship wake (relatively) far downstream the ship. For this, we want to study the potential effects of the mixing of the water column that the turbulent and rotating flow behind the ship causes. Both bottom-reaching disturbances in shallow water as well as breaking up of stratification are of interest changing the environment in the ocean. Here, we will also work with optimisation of the system. Funding for the research comes from the Chalmers, the Swedish Transportation Agency, Kongsberg Maritime Sweden AB, and the Swedish Agency for Water and Marine Management (HaV).