Title:	Scale resolved flow simulations for hydroacoustics
DNr:	NAISS 2024/5-539
Project Type:	NAISS Medium Compute
Principal Investigator:	Rickard Bensow <rickard.bensow@chalmers.se>
Affiliation:	Chalmers tekniska högskola
Duration:	2024-11-01 – 2025-11-01
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 focus area for this project is to advance our capability to perform hydroacoustic simulations to assess underwater radiated noise from ships. The main concern relates to predicting the cavitation dynamics, and the consequence in terms of 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 to capture this dynamics, resolving the internal structure of the developing cavities on the propeller blades as well as the trailing tip vortex cavitation. In some of these processes, also compressibility may need to be considered requiring very small time steps in water. To tackle this problem, we will study both simplified geometries as well as try to expand to full ship configurations. Some fundamental work will be done for the turbulence modelling, looking into modelling and resolution demands to correctly capture the flow over lifting surfaces (such as propeller blades) and the tip vortex development. These studies are done in two international collaborative efforts looking at modelling requirements (for example wall-modelled LES) to correctly capture the physics for boundary layers over curved surfaces and tip vortex cavitation respectively. Further using simplified geometries, we will develop improved techniques to model the radiated sound from cavitating flows. This work is part of a newly started European project on assessing and mitigating noise emissions from ships, the BluEcho project. We have in previous work documented issues in current established techniques that will be further documented here, and we will look into promising alternatives for a correct prediction. Also in BluEcho, we will study measures to reduce the noise emissions by studying different ship configurations or modes of operation. This work will start during the current project period, but will primarily carry on into 2025. Funding for the research comes from the BluEcho EU project (administered by FORMAS) Chalmers, the Swedish Transportation Agency, and Kongsberg Maritime Sweden AB.