High-Thrust CoFlow Jet Cylinder Wind Sail at Varying Wind Directions (2-D Part)

What is it about?

Global marine shipping delivers over 80% of the goods in the world. As the Paris Agreement comes into effect, there is an increasing demand to reduce marine shipping fossil fuel consumption and carbon emissions. A part of this demand can be realized by introducing rigid wind sails to modern ships, which use the wind energy to generate a part of the propulsion force. This paper provides a theoretical rigid sail solution by applying CoFlow Jet to cylinder wind sails. Instead of the traditional Flettner rotor that is rapidly spinning, CFJ cylinder sail does not spin by itself. This paper numerically studies the 2-D performance of a CFJ cylinder at different wind directions, represented by angles of attack, and jet strength. The in-house Reynolds-averaged Navier-Stokes (RANS) solver, FASIP, is used in simulation, where SA turbulence model and the dual-time step method is used.

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Photo by Ivan Bandura on Unsplash

Photo by Ivan Bandura on Unsplash

Why is it important?

The numerical results of 2-D CFJ cylinders indicate that the CFJ cylinder has the potential to provide very high lift coefficient at low drag and low power consumption with a large tolerance range of AoA. Such features are very beneficial as rigid wind sails for shipping. A comparative analysis of the lift coefficients, drag coefficients and energy expenditure at various jet momentum coefficients and angles of attack are conducted. When Cμ = 0.5, the lift coefficient at zero angle of attack reaches 12.63. The power coefficient at this flow condition is only 5% of CL, resulting in a CL/CD,c of 19.92. When Cμ is increased to 2.0, the lift coefficient reaches 25.13, about doubled, but the power coefficient is increased exponentially by 10 times. As AoA varies from -90◦ to 90◦, the lift does not vary much within AoA of ±20◦ at high CL level of 20. At a lower CL level of 12, the CL has a much broader insensitive range to AoA from -20◦ to +60◦. The drag coefficient and CFJ power coefficients are also similar.

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