Can CFD (Computational Fluid Dynamics) Replace Model Tests in Ship Propeller Design?
Author: Jeroen Berger • Publication date:
When designing and optimizing ship propellers, Computational Fluid Dynamics (CFD) is increasingly used as a primary design tool. With this numerical flow analysis, the water flow around the propeller, the afterbody and relevant appendages, such as the rudder and nozzle, can be simulated digitally. The influence of flow-conditioning devices can also be included when they materially change the inflow to the propeller. Examples include Energy Saving Devices (ESDs) such as a Pre-Duct, a Pre-Swirl Stator (PSS), a Propeller Boss Cap Fin (PBCF), a Twisted Rudder and a Rudder Bulb. Based on such simulations, design choices can be substantiated at an early stage.
For shipping companies and shipowners, this can offer practical advantages. CFD provides faster insight into expected efficiency within a specific operational profile, reduces the number of iterations during development and supports better substantiation of potential fuel and emissions effects, provided input data and the computational approach align with the intended application. At the same time, the core question remains nuanced in practice: to what extent can CFD replace physical model tests, such as towing-tank tests and cavitation investigations, when reliability, validation and class acceptance must be assured?
This article explains where CFD is demonstrably strong in propeller design, which uncertainties arise particularly with cavitation and unsteady inflow, and why validation with model tests still plays a decisive role in many projects. It then sets out how a hybrid approach is built in practice, in which CFD results, test data and class and client acceptance requirements are brought together in a single consistent and auditable substantiation.
Strengths of CFD
Computational Fluid Dynamics adds particular value in clarifying complex flow phenomena that conventional measurement methods can capture only to a limited or indirect extent. By computing the flow numerically, it becomes possible to analyze in detail how velocity distributions, pressure fields, vortex structures and interactions develop around the propeller, the hull form and any stern components. This enables assessment not only of overall performance, but also of local effects that directly influence efficiency, loading and cavitation sensitivity.
A key advantage of CFD lies in flexibility during the design phase. Variants in blade geometry, pitch distribution, diameter and positioning relative to the hull and rudder can be evaluated relatively quickly, without manufacturing a new physical model for each change. The influence of flow-conditioning devices, such as Energy Saving Devices, can also be included at this stage, provided the modeling is set up carefully and consistently. This yields early insight into trends and relative differences between design options, rather than only after costly and time-consuming test setups.
For shipping companies and shipowners, this translates into a more efficient and better-substantiated decision-making process. CFD makes it possible to assess the expected effect of a propeller design or optimization within a specific service profile and speed range before physical tests are undertaken. This shortens development and reduces the risk that a design choice proves suboptimal late in the process. The strength of CFD does not lie in absolute certainty, but in systematically comparing and substantiating design choices based on consistent assumptions and reproducible analyses.
Limitations and Validation
At the same time, Computational Fluid Dynamics has inherent limits. The reliability of outcomes depends strongly on the computational models, boundary conditions and assumptions used to describe the flow. Turbulence modeling, rotating reference frames and computational-grid resolution directly affect results. Relatively small differences in modeling can therefore produce noticeable variations in predicted forces, efficiency or pressure distributions.
These limitations are most visible with cavitation. The inception, stability and collapse of vapor cavities are highly non-linear and time-dependent processes that numerical models can only approximate. Although modern cavitation models provide valuable insight into trends and relative sensitivities, uncertainties remain in exact intensity, noise levels and erosion potential. This effect is amplified under unsteady inflow, such as a non-uniform wake aft of the hull or varying loads due to maneuvers and changing water depth.
For these reasons, CFD in practice is almost always coupled to physical model tests. Towing-tank tests and cavitation-tunnel investigations provide reference data against which numerical results can be checked and calibrated. This validation establishes whether the computational approach is representative for the intended operating point and allows deviations to be identified in time. The combination of CFD and model testing ensures that digital predictions do not stand alone, but demonstrably align with measurable reality and with client and class acceptance requirements.
Complementary Rather Than Replacing
The common position in the maritime sector is that Computational Fluid Dynamics does not fully replace model tests, but is deployed primarily as a complement. In the design phase, CFD provides speed and flexibility, because variants in blade geometry, stern configuration and inflow conditions can be evaluated and compared relatively quickly. When substantiation for decision-making, contracting or class must be demonstrable and verifiable, physical model testing remains valuable, for example to establish cavitation behavior, pressure pulses and vibration risks reliably under representative and varying operating conditions.
For shipping companies and shipowners, this typically results in a hybrid approach. CFD guides design choices and helps select promising variants efficiently. Towing-tank tests and cavitation investigations then provide the verification with which predictions can be confirmed, bounded or, where necessary, corrected. The result is a substantiation that is efficient during design and at the same time sufficiently auditable for the client, yard and class, with reproducible and traceable assumptions, settings and measurements.
Strategic Value for the Sector
The combination of Computational Fluid Dynamics and physical model testing makes it possible to align propeller designs more closely with rising requirements from regulation and market developments. By clarifying hydrodynamic performance early in the design process and then verifying it with model tests, shipyards and designers can steer more effectively on propulsive-power demand, cavitation control and operational robustness within the intended deployment profile.
In that context, the hybrid approach supports substantiation of measures relevant to frameworks such as MARPOL Annex VI, the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII). Its value does not lie in claiming absolute performance gains, but in improving the predictability of hydrodynamic behavior and energy use across diverse operating conditions. That predictability is becoming increasingly important as performance is assessed over longer periods and within tightly defined reference frameworks.
For shipping companies and shipowners, this means that CFD, in conjunction with model tests, can contribute to better-substantiated investment decisions. Not as a standalone solution for compliance or emissions reduction, but as part of a systematic design and validation approach that makes efficiency improvements demonstrable and verifiable. In this way, the role of CFD grows from a purely technical tool into a strategic instrument within future-proof fleet management, in which technical feasibility, class acceptance and regulation are assessed consistently in concert.
About This Article
This article forms part of the background information on the propeller as a product and falls within the cluster Ship Propeller Validation, CFD and Performance Measurement. Its core premise is that Computational Fluid Dynamics (CFD) is a powerful predictive tool within propeller design, but that the extent to which model tests can be replaced is constrained by validation requirements and by the demonstrability of performance under representative operating conditions. For that reason, CFD results only gain full significance when outcomes are traceably linked to model testing and, where relevant, to in-service measurements. For a project-specific elaboration, the page Custom Ship Propeller logically builds on this topic.
For insight into the propeller configurations and applications to which CFD and model testing are applied, What Types of Ship Propellers Are There and What Are Their Characteristics connects logically, because that article outlines the functional and hydrodynamic field within which design analyses take place.
The limitations of numerical predictions are most evident in practice with cavitation and unsteady inflow. In that context, What Is Cavitation and How Does It Affect Ship Propellers provides direct depth, because it explains why this phenomenon typically requires physical validation.
For the step from design to demonstrable acceptance, How Is Ship Propeller Performance Measured and Validated fits best, because it sets out how CFD results, model tests and in-service measurements are combined in a verifiable and reproducible substantiation for the client and class.