An Investigation into the Impact of Air Ingress on Propeller Propulsive Characteristics Due to the Use of Air Lubrication

Hitchmough, D (2025) An Investigation into the Impact of Air Ingress on Propeller Propulsive Characteristics Due to the Use of Air Lubrication. Doctoral thesis, Liverpool John Moores University.

Text 2025DavidHitchmoughPhD.pdf - Published Version Access Restricted until 23 June 2026. Available under License Creative Commons Attribution Non-commercial. Download (7MB)

Abstract

Air lubrication is considered a promising drag-reduction technology in the marine sector. It has seen increased interest as global shipping endeavours to meet environmental targets. The technology can decrease a ship's skin frictional drag, reducing its Carbon Intensity Indicator (CII) ratings. The principle of air lubrication is that by introducing air into the near wall region of a ship’s hull, the introduced air modifies the flow characteristics and reduces the resistive effect of the water and drag. Many critical questions must still be answered regarding the efficacy of its use as a drag-reduction approach. Specifically, in the context of this thesis, the potentially harmful effects of using the technology on the propeller's propulsive characteristics and the broader impact on the propeller blades and shaft should be considered (Such as force instability and vibration). This work aimed to assess the impact of varying quantities of air being introduced into the propeller plane at varying advance coefficients while simultaneously evaluating the effect of this air ingress on the propeller's propulsive characteristics.
This research utilises a Computational Fluid Dynamics (CFD) software package, STAR-CCM+. Firstly, an initial single-phase simulation approach for the propeller was determined. Secondly, a novel multi-phase approach was developed to simulate air lubrication and propeller interaction. The multi-phase approach is based on Eulerian multi-phase modelling, and the Eulerian approach is further developed by utilising population balance modelling. The use of Population balance modelling allows for the air to be expressed in a particulate/bubbly manner. Three air injection rates (High, Medium and Low) were considered for each advance coefficient ranging from 0.1 to 0.9. The air injection rates were determined by evaluating the air injection coefficient (the ratio of injected air flow to water flow). The High, Medium and Low cases have injection coefficients of 0.7, 0.5 and 0.3, respectively.
The results and outcomes of this work showed that air ingress in the propeller plane has a detrimental effect on the propeller's propulsive characteristics and a potential impact on the broader propulsion system as shown by force variance in the propeller shaft and blades. The primary focus of assessing this impact was on the thrust and torque coefficient. Still, the work also elucidated the possible implications of cavitation and force instability across the propeller blades, which can induce vibration in the propulsive system. The detrimental effects of the technology on the propeller must be considered when discussing the viability of the technology as a decarbonisation technology holistically.
3
As an additional outcome of the work, the distribution of air and bubble size was elucidated through the use of Eulerian multi-phase modelling and further elucidated in regard to size distribution by the use of population balance modelling. This impact of the propeller upon the air, rather than the converse aim of the air upon the propeller, is useful in considering modelling air lubrication topographies.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	CFD; Fluid Dynamics; Computational Fluid Dynamics; Air Lubrication; ALS; Propeller; Propulsion; Marine; Marine Engineering; Engineering; Marine Architecture; Decarbonisation; Marine Decarbonisation
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Divisions:	Engineering
Date of acceptance:	10 May 2025
Date Deposited:	24 Jun 2025 11:18
Last Modified:	24 Jun 2025 11:18
DOI or ID number:	10.24377/LJMU.t.00026464
Supervisors:	Blanco-Davis, E, Armin, M, Seddighi, M and Wang, J
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26464

View Item