In English

Numerical Modelling of Steady and Unsteady Sail Aerodynamics

Adam Persson
Göteborg : Chalmers tekniska högskola, 2016. 68 s. Report. X - Department of Shipping and Marine Technology, Chalmers University of Technology, Göteborg, Sweden, 2016.
[Examensarbete på avancerad nivå]

A method for prediction of aerodynamic forces produced by a jib and main sail plan for steady and unsteady upwind conditions has been developed, and validated against experimental results. Computational uid dynamics, with a RANS approach, is used to model the viscous ow on a sti , model scale sail plan, where the sail shape has been captured in the experimental studies used for validation. An unstructured, overset grid is used, allowing movement of the sail plan. Two rounds of simulations were performed, where the second was started since the tunnel geometry as well as experimental results used for the rst round of simulations proved to be incorrect. Correct tunnel geometry and experimental results were later provided by one of the authors of the experimental paper. For the initial simulations, a veri cation and validation was performed for steady con- ditions. The veri cation was successful, and the solution shown to have insigni cant grid dependence for the tested grids. However, due to undocumented corrections applied to the experimental data, the validation was unsuccessful, showing large di erences. This prompted an investigation concerning physical modelling, where the e ects of tunnel conditions, turbulence modelling, scale e ects as well as grid topology were investigated. For the nal simulations, the correct tunnel geometry was used, and results of the physical modelling investigation were considered. Again, veri cation and validation were performed. In contrast to the veri cation in the initial round of simulations, some grid dependence is apparent for the tested range of grids. For the steady case, the subsequent validation was successful, with a 2:8% di erence for the driving force coecient Cx and a 3:2% di erence for the side force coecient Cy. The method was also validated for one unsteady, pitching case. A low amplitude, high frequency pitch motion was tested, and showed good agreement for mean values, with a 2:1% di erence for the driving force Fx and a 3:6% di erence for side force Cy. The phases of the forces were well predicted but force amplitudes were under predicted, with a 14:3% di erence for the amplitude of Fx, and a 18:5% di erence for the amplitude of Fy. The prediction of mean value and amplitude for vertical centre of e ort zCE was poor, with a 10:2% di erence for the mean value, and a 52% di erence in amplitude.

Nyckelord: Sail aerodynamics, steady, unsteady, CFD

Publikationen registrerades 2017-03-07.

CPL ID: 248455

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