Rising fuel prices and IMO pressure to reduce the energy efficiency design index have renewed interest in energy saving devices (ESDs). Many ESD concepts date back to the 1970s, when the first oil crisis triggered worldwide research activities to make ships more fuel efficient. A joint industry project between Hyundai Heavy Industries (HHI) and DNV GL take a fresh look at Grim’s vane wheel.
In later decades, many interesting ideas were abandoned again, as low energy prices deflected the focus on building prices rather than fuel efficiency.
“It is time to look at some of the great ideas of that time”, says Woo-Chan Seok, project manager at Hyundai Heavy Industries (HHI). “Especially Grim’s vane wheel has not received the attention it deserves.”
This was the starting point of a joint industry project between HHI and DNV GL.
Professor Otto Grim, director of the Hamburg Model Basin in the early 1970s, developed and patented the vane wheel, a freely rotating device located behind the propeller. The vane wheel consists of a turbine portion and a propeller portion. The main function of the vane wheel is to extract energy from the propeller slipstream in the turbine portion and convert this energy into additional thrust in the propeller portion. In the 1970s, Grim’s vane wheel was shown to give 5% to 10% improvement in required power, exceeding the fuel savings that can be expected from most any other ESDs.
However, after some 60 installation, the high-profile case of the “Queen Elizabeth 2” sealed the fate of the vane wheel for decades to come. The QE2 was refitted in 1986 with vane wheels. During her first voyage, some of the blades broke off and the remaining vanes were all removed. The reputation of being mechanically too sensitive stayed, even though years later the investigation ruled that inappropriate grease had been used. “With the lessons learnt back then, and our modern capabilities for flow simulations and structural investigations, it is time to take a fresh look at Grim’s vane wheel”, says fluid dynamics expert Dr. Vladimir Shigunov of DNV GL.
The JIP team combined intelligently fast and simpler models where possible with advanced CFD (Computational Fluid Dynamics) tools where required, forming a design and analysis approach that is both efficient and accurate. Results for model scale were validated against experiments in HMRI (Hyundai Maritime Research Institute) model basin. As there is no extrapolation method to full scale available for the vane wheel, CFD was used for extrapolation to full scale.
The results of the JIP indicate that correct prediction of the wake field is necessary in simulations to obtain good agreement with model tests. The wake field in model scale seems to be much more sensitive to the employed turbulence model than in full scale. The differences in the wake field between model and full scale explain also the significant differences in performance of the vane wheel between model and full scale. “Using high-fidelity CFD is really the only way forward for the design of such energy saving devices”, summarizes DNV GL’s CFD group leader Tobias Zorn.
Source: DNV GL
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