An Experimental Study on Visualisation and Passive Control of Model Propeller Boundary Layers

This paper examines the complications of a laminar propeller boundary layer during towing tank model testing and proposes a solution in the form of turbulence stimulation to improve the consistency and reliability of model testing procedures. Although common for model ships and their appendages, this approach is novel for propellers in the maritime industry. In an effort to promote widespread adoption, this paper presents two innovations.
The first is a modernised experimental method for conducting propeller paint tests to visualise the boundary layer flow. We validate this method, highlight key considerations, and provide illustrative examples for a comprehensive understanding.
The second innovation is the development of ’turbulators’, a novel, low-cost and practical technique for inducing a turbulent boundary layer on model propellers. By systematically varying the height of the turbulators for a test-case propeller, it was possible to estimate their isolated effect on propeller performance. The results show that turbulators impose only a marginal penalty of 0.1% on both open water efficiency and thrust. However, the transition to a turbulent boundary layer regime resulted in a significant difference of 4.9% in efficiency and 12.9% in thrust for this particular test-case propeller.
In order to support the recommendation for the application of turbulence stimulation to model propellers, this study analysed a number of contemporary propeller designs. The methodology involved quantifying the effect of turbulence stimulation on propeller performance. In addition, the boundary layer was examined both with and without turbulence stimulation using paint tests. The comparative analysis of the different propeller types revealed varying degrees of sensitivity to low Reynolds number effects and the impact of turbulence stimulation. This sensitivity was particularly pronounced for propellers with smaller blade areas, where turbulence stimulation significantly reduced efficiency.
In summary, this research enhances the understanding of boundary layer behaviour on model propellers and suggests the use of turbulence stimulation to improve the consistency of model testing. These advancements provide the basis for more accurate predictions of full-scale performance and ultimately contribute to the development of more efficient marine propulsion systems.