Actuator Line Methods for Non-Conventional Offshore Renewable Energy Applications

Project Aims

The aim of this project is to refine and enhance the Oxford in-house OpenFOAM embedded actuator line method (ALM) software to allow for the modelling of non-conventional marine ORE devices. The ALM code is currently validated for conventional offshore renewable energy applications such as horizontal axis turbines. The project will benefit from a national collaboration with Dr Pal Schmitt from Queen’s University Belfast (QUB) who is an expert in both OpenFOAM programming and marine CFD simulations. 

Under the project the code will be refined to develop a high-quality software, which allows modelling of blades of alternative offshore renewable energy devices such as transverse axis crossflow turbines (TACT). The numerical wave tank simulation framework, provided by Dr Schmitt will be integrated with the ALM. The software will be validated against loads and flow measurements from a fully instrumented TACT developed by the Ocean Renewable Power Company’s (ORPC), aiming to be among the first validation studies of the ALM for the numerical modelling of TACTs. 

The  project addresses the need for a generalisable and well documented actuator line tool for marine applications, by establishing a collaboration between an ALM and a marine CFD expert and is amongst the first validations of the ALM for crossflow turbines against experimental data. 

Dr Markella Zormpa, University of Oxford

This project emerged from discussions during the OceanFOAM Hackathon 2024 in Røsnæs, Denmark. There, a need for a modular implementation of the actuator line method (ALM) in OpenFOAM was highlighted, able to support several applications other than horizontal axis turbines. Special attention was given to modelling cross-flow turbines, an intersection of interests between Pal Schmitt from Queen’s University Belfast (QUB), ORPC, and myself. The question of implementation as well as applicability of the ALM for similar devices is an active research topic.

The funded project involved:

1. Two week-long visits to QUB: knowledge transfer in the topics of actuator methods, OpenFOAM, and cross-flow turbine hydrodynamics was the primary goal of the visits. The QUB group and ORPC have extensive experience in cross-flow turbine hydrodynamics, with activities in experiments, design, simulations and OpenFOAM solvers. My research has centred around horizontal axis turbine aerodynamics, and their ALM modelling in OpenFOAM. Consequently, conversations on the hydrodynamics of cross-flow turbines and their ALM modelling were fruitful. Measurements from ORPC’s fully instrumented cross-flow turbine constitute a rare validation dataset to be used. However, the question of applicability of the ALM for transverse axis marine devices emerged during talks, an active research topic. Cross-flow turbines are subject to a range of complex hydrodynamic interactions, absent in horizontal axis turbine aerodynamics. Further studies into this question led to the project described in the next activity.
2. Numerical modelling of cross-flow turbines: Before proceeding to the full 3D simulation of a cross-flow turbine, a spanwise section of the device was first simulated using a 2D actuator framework implemented for this work in OpenFOAM (supported by activity (4), see below) to allow for a reduction in the sources of uncertainty for the problem. The aerofoil loads calculated using the ALM were compared to blade-resolving (BR) simulation results performed by QUB: the ALM could capture the main load trends predicted by the BR methods, however further calibration is required for the more complex regions of the blade sweep.
3. MARINE 2025 Conference, Edinburgh, Scotland 23-25 June 2025 (conference fees and travel not directly funded by the grant): the work of activity (2) was summarised in “Numerical modelling of cross-flow turbines: 2D blade-resolved against 2D actuator line method simulations, M. Zormpa, J. L. Johnston, C. R. Vogel, P. Schmitt, Oral Presentation, MARINE 2025.” Furthermore, two oral presentations between QUB, ORPC, and the University of Oxford on crossflow-turbines were presented by other project collaborators.
4. Programming CFD, OpenFOAM Training, CFD Direct: A three-day long OpenFOAM programming course was ideal for consolidating several OpenFOAM coding concepts. This has contributed to progress toward generating generic ALM classes within our in-house Oxford ALM software, part of a wider effort of generalising the ALM code.
5. Ongoing collaboration: we are continuing to collaborate and meet monthly with QUB, to discuss further progress on the continuation of activities (2) and (4).

From a broader perspective, the topic of marine energy modelling using affordable hydrodynamic models such as the ALM is crucial for the upscaling of marine renewables.