With the recent advent of high-end computing power, computational fluid dynamics (CFD) has become an indispensable tool in the marine industry. Beyond predicting performance parameters, a detailed flow pattern study enables designers to better design products to avoid undesirable flow features, such as separation on the housing, which in addition to increased drag can also subject the propeller to significant non-uniform inflow.
Ship-scale CFD is now gaining traction in a much broader way when it comes to propulsion solutions – from the predesign stage to final tailoring of the unit’s propeller blades. These state-of-the-art computational tools have also greatly extended our design capabilities at Steerprop, enabling our designers to offer tailor-made solutions.
Below are just some of the ways that ship-scale CFD is bringing new benefits to vessel designers, shipowners and system integrators.
Choice of propulsors: When shipowners select the right propulsion units for their vessels, the decision is still primarily based on comparative performance using model scale tests.
With a greater shift towards using azimuth propulsors in modern ships, however, unit performance is significantly affected by scale effects. The reliability of traditional empirical methods in scaling the performance of these units, especially ducted ones and podded propulsors, is still a great concern. Therefore, a need is opened up to supplement model scale tests with CFD tools to accurately predict the azimuth propulsor performance.
Shape your housing: An optimized gear housing is essential from the perspective of overall azimuth propulsor unit performance. CFD, coupled with 3D modeling tools, has enabled us to carry out detailed investigations by defining and optimizing the housing in terms of geometry parameters, like housing length, torpedo diameter, strut distance from propellers and more.
A better understanding of their individual and combined effects through interaction on overall propulsor performance has enabled designers at Steerprop to better design our units, even in off-design and steering conditions.
With developed accuracy and confidence in modern computational tools, our focus has nowadays been more on optimizing the housing and thus our units at ship scale, rather than defining the unit’s performance with model tests.
Design your propeller for actual flow conditions: In times when there are conflicting design requirements for minimum-to-no-cavitation, low-noise and high-efficiency propeller units, it becomes more essential for designers to ensure that the inflow conditions are properly captured.
Traditionally, the design of propeller blades considers the nominal wake data obtained from model test and couples it with not-so-reliable empirical extrapolation schemes. Today, computational tools, like BEM-RANS coupling, further improve the design process by making ship-scale effective wake available.
This has greatly improved our ability to predict behind-the-ship cavitation performance and thus avoids overly conservative designs.
A sea of new opportunities
The integration of these tools in our daily design process, with the level of detail in their prediction, is limited only by computing power. Additionally, the growing availability of on-board monitoring data on modern vessels will further extend the reliability and performance of these tools in days to come. At Steerprop, we’re always on the lookout for new ways to put our computational tools to use for improved propulsion power.
About the author:
Mahish Mohan brought his CFD knowledge to Steerprop just over one year ago. He is now driving the company’s and team’s capabilities forward in their use of computational tools for tailor-made customer solutions. After Steerprop brought this advanced capability in-house, the company now has a competitive edge when putting this special expertise into practice.