Numerical prediction of propeller induced hull pressure pulses and noise
Doktorsavhandling, 2021

An operating marine propeller is one of the major sources inducing hull pressure pulses, onboard noise and vibration as well as underwater radiated noise. There are rising concerns of environmental impacts and comfort and welfare of passengers and crews due to these negative effects. Cavitation is a significant source of these effects, but it is typically inevitable if only the hydrodynamic efficiency of the propeller is optimized. To reduce the noise and the pressure pulses caused by the cavitation, a trade-off of the hydrodynamic efficiency should be made to design and optimize a propeller that possess both high hydrodynamic performance and low noise and hull pressure pulse generation. More accurate predictions are needed to identify the best trade-off between a high efficiency propeller design and a low pressure pulse and noise one.

The study focuses on the numerical prediction of hull pressure pulses and radiated underwater noise using viscous CFD including the opensource package OpenFOAM and commercial package Star-CCM+. Numerical predictions are performed regarding different experimental configurations for determining hull pressure pulses and ship noise, including propellers mounted on inclined shafts and propellers operating behind ship hulls, under different scales and scaling laws with different operating conditions and Reynolds numbers.

Non-cavitating propeller induced pressure pulses are generally lower in levels and rich in blade passing frequency comparing to cavitating conditions, with blade tip clearance as a major impact factor. For cavitating conditions the rate of cavity growth/shrinkage is found to play the dominating role generating pressure fluctuations. For certain model scale configurations, numerical predictions with ordinary approaches predict massive sheet cavity on propeller blades leading to pressure pulse prediction discrepancies comparing to experimental observations and measurements. These can be significantly improved by a developed bridged model considering laminar to turbulence transition. Tip vortex cavitation bursting is a common phenomenon found on propellers operating behind the ship hull and generating significant levels of pressure pulses. The phenomenon is numerically predicted with investigations of its generation mechanisms in relation to the propeller inflow, convex shaped sheet cavitation closure line and traveling re-entrant jet underneath the sheet cavity.

Propeller induced noise prediction was studied using approaches focused on the FWH (Ffowcs Williams-Hawkings) acoustic analogy with incompressible input on permeable/porous data surface (PDS).  Studies show this combination between incompressible input and FWH acoustic analogy can be erroneous, though using certain PDS placements and closer receivers the error can be reduced.

FWH acoustic analogy

Pressure pulses

Hydroacoustics

RANS

IDDES

Sheet cavitation inception

Ship noise

k − ω SST

Transition

Cavitation

Room FB, building Fysik Origo, Chalmers
Opponent: Prof. Mehmet Atlar, University of Strathclyde, United Kingdom

Författare

Muye Ge

Chalmers, Mekanik och maritima vetenskaper, Marin teknik

Numerical investigation of pressure pulse predictions for propellers mounted on an inclined shaft

Proceedings of the Sixth International Symposium on Marine Propulsors,; Vol. 1(2019)p. 284-292

Paper i proceeding

Numerical investigation of propeller induced hull pressure pulses using RANS and IDDES

Proceedings of IX International Conference on Computational Methods in Marine Engineering,; (2021)

Paper i proceeding

M. Ge, U. Svennberg, R.E. Bensow. Improved shet cavitation inception prediction using bridged transition sensitive turbulence model and cavitation model. Submitted to Journal of Marine Science and Engineering.

M. Ge, U. Svennberg, R.E. Bensow. Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input. Submitted to Ocean Engineering.

For operating marine propellers, the propulsion force is related to the pressure differences that are created on the two sides of the propeller blades via the rotational motion of the curved blades. The pressure on the propeller blades can drop below water saturation pressure and the tension force can break the water medium, known as cavitation, which contributes significantly to the hull pressure pulses and radiated underwater noise. However, cavitation is typically inevitable for propellers with optimized propulsion efficiencies. To reduce the noise and the pressure pulses caused by the cavitation, a trade-off of the hydrodynamic efficiency should be made to design and optimize a propeller that possess both high hydrodynamic performance and low noise and hull pressure pulse generation. Due to rising concerns of environmental impacts and comfort and welfare of passengers and crews, more accurate predictions are needed to identify the best trade-off between a high efficiency propeller design and a low pressure pulse and noise design.

Model scale experiments may take weeks to months which are costly and usually performed at a late stage of the design process. With the increase of computational resources, numerical methods are developing rapidly as a supplement and alternative approach, which is typically faster, cheaper and may provide more detailed flow information compared to model testing. In the thesis, we focus on the numerical prediction of propeller induced pressure pulses and noise using CFD(Computational Fluid Dynamics). To be more specified, we studied the sheet cavitation inception on a hydrofoil under various conditions with a developed model and extended to the analysis of model scale marine propellers. We also present predictions and analysis of induced pressure pulses of standalone propellers and propellers behind different ship hulls in different scales including both model scale and full scale configurations. The far-field underwater radiated noise was predicted using incompressible flow input together with an acoustic analogy and further investigated using simplified but representative configurations to explain the gap between numerical predictions and experimental measurements. It is my hope that the work can be useful for further propeller design developments.

Ämneskategorier

Strömningsmekanik och akustik

Marin teknik

ISBN

978-91-7905-586-8

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5053

Utgivare

Chalmers tekniska högskola

Room FB, building Fysik Origo, Chalmers

Online

Opponent: Prof. Mehmet Atlar, University of Strathclyde, United Kingdom

Mer information

Senast uppdaterat

2021-11-03