Marine Propulsion System Performance Beyond the Propulsive Factors
Doctoral thesis, 2021

The marine propulsion system often operates in the wake of the ship it is mounted on. This implies that the propulsion system affects the flow around the hull, and the inflow to the propulsion system is dependent on the hull shape. Due to the complexity of the flow, the performance of marine propulsion systems has historically been assessed through model-scale testing in basins, alternative numerical tools were for a long time not available. However, the limited possible measurements does not provide any detailed descriptions of the propulsion system performance. A second factor complicating the use of model-scale testing is the inevitable low Reynolds number in relation to the real ship. The need for a more detailed description of the propulsion system performance motivates the use of Computational Fluid Dynamics (CFD); there are no limitations on what to extract in terms of flow details or forces on surfaces and it can be applied for the ship-scale system. However, this requires a representative model of the flow in ship-scale which is not yet well established. In this thesis, using CFD, two alternative approaches to the propulsive factors originating from the model-test scaling procedure are proposed to describe the propulsion system interaction effects: A detailed evaluation of forces on the propulsion system and hull surfaces and a control volume approach based on energy fluxes describing the power required by the propulsion system in terms of various energy fluxes. For the first approach a powerful tool is the thrust over torque coefficient for a blade around a revolution, or studies of its radial distribution at specific positions. A clear advantage of the control volume approach is its possibilities to describe the viscous losses. As a step towards ship-scale CFD a review and comparison of different methods to model hull roughness is conducted; it shows no convergence towards specific roughness functions or methods to obtain the roughness length scales and there is neither a strong correlation between the additional resistance predicted by various hull roughness models and the Average Hull Roughness (AHR). Applying the proposed approaches, a few generic interaction effects could be explained. For instance: The old rule of thumb regarding optimal propeller diameter in-behind based on model-scale tests from the 1950s is shown to be mainly due to that operation together with a rudder favours smaller propeller diameters since the rudder can make use of the stronger slipstream rotation. However, the results indicate that this only holds within the same scale factor, and the optimal propeller diameter for the ship is most probably larger than what is indicated by propeller series data. Other generic interaction effects explained is how tip-unloading deteriorates propeller performance to a larger extent in-behind since the wake distribution further decreases the load on the blade tip, and how blunter leading edges has a superior performance at low load, since they are less sensitive to poor performance at negative angles of attack.

CFD

Energy balance analysis

Propulsor-hull interaction

RANS

SB-H1, Sven Hultins gata 6
Opponent: Prof. Tom van Terwisga, TU Delft / MARIN, Netherlands

Author

Jennie Andersson

Chalmers, Mechanics and Maritime Sciences, Marine Technology

Energy balance analysis of a propeller in open water

Ocean Engineering,; Vol. 158(2018)p. 162-170

Journal article

Energy balance analysis of model-scale vessel with open and ducted propeller configuration

Ocean Engineering,; Vol. 167(2018)p. 369-379

Journal article

Review and Comparison of Methods to Model Ship Hull Roughness

Applied Ocean Research,; Vol. 99(2020)

Journal article

On the Selection of Optimal Propeller Diameter for a 120-m Cargo Vessel

Journal of Ship Research,; Vol. 65(2021)p. 153-166

Journal article

Andersson, J, Gustafsson, R, Johansson, R and Bensow, R.E. Propeller Hull Interaction Beyond the Propulsive Factors

The marine propulsion system, i.e. the propeller together with other possible appendages such as rudder, duct and energy saving devices, often operates in the wake of the ship it is mounted on. This implies that the propulsion system affects the flow around the hull, and the inflow to the propulsion system is dependent on the hull shape. Due to the complexity of the flow, the performance of marine propulsion systems has historically been assessed through model-scale testing in basins, alternative numerical tools were for a long time not available. However, the limited possible measurements do not provide any detailed descriptions of the propulsion system performance. A second factor complicating the use of model-scale testing is different flow characteristics in relation to for the real ship. The need for a more detailed description of the propulsion system performance motivates the use of computer simulations of the flow, so called Computational Fluid Dynamics (CFD); there are no limitations on what to extract in terms of flow details or forces on surfaces and it can be applied for the ship-scale system. In this thesis, using CFD, two approaches are proposed to describe the propulsion system interaction effects: A detailed evaluation of forces on the propulsion system and hull surfaces and a control volume approach based on energy fluxes describing the power required by the propulsion system in terms of various energy fluxes. Describing the propulsion system performance based on CFD requires a representative model of the flow. As a step towards ship-scale CFD a review and comparison of different methods to model hull roughness is conducted; but more research, including ship-scale flow measurements, are required to increase the maturity of ship hull roughness modelling. Applying the proposed approaches, a few important aspects for the marine propulsion system design, are explained. For instance, how propeller operation together with a rudder favors smaller propeller diameters since the rudder can make use of the stronger slipstream rotation of the inevitably higher loaded blade sections of a smaller propeller. But also, how the optimal propeller diameter varies between model and ship since the viscous losses are higher for the model-scale flow. Another design aspect studied is how unloading the blade tips deteriorates propeller performance to a larger extent in the wake in relation to a homogeneous inflow since the wake distribution further decreases the load on the blade tips. It is also shown how blunter blade leading edges has a superior performance at low load, which is beneficial when the propeller operates in a wake field with large variations in operating conditions around a revolution.

Analysis and optimisation of marine propulsion systems - part 2

Kongsberg Hydrodynamic Research Centre, 2019-01-01 -- 2021-06-30.

Swedish Energy Agency (38849-2), 2019-01-01 -- 2021-06-30.

Impact of surface roughness on propeller design and ship maintenance (RÅHET)

Swedish Transport Administration (6771), 2018-05-01 -- 2020-05-01.

Improved prediction methods for ships –Energy Saving Devices

Swedish Transport Administration (EF1015,ärende6770), 2019-01-01 -- 2021-12-31.

Analysis and optimisation of marine propulsion systems

Rolls-Royce (Swe), 2014-10-06 -- 2017-09-30.

Swedish Energy Agency (38849-1), 2014-10-06 -- 2017-09-30.

Areas of Advance

Transport

Infrastructure

C3SE (Chalmers Centre for Computational Science and Engineering)

Subject Categories

Vehicle Engineering

Fluid Mechanics and Acoustics

ISBN

978-91-7905-566-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5033

Publisher

Chalmers University of Technology

SB-H1, Sven Hultins gata 6

Online

Opponent: Prof. Tom van Terwisga, TU Delft / MARIN, Netherlands

More information

Latest update

11/3/2021