Effect of Hydrofoils’ Twist on the Lift-Drag Characteristics Based on Serial Production Sampling

  • Macikowski, Zbigniew (Gdańsk University of Technology)
  • Krata, Przemysław (Gdańsk University of Technology)
  • Karczewski, Artur (Gdańsk University of Technology)

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Hydrofoils are designed to achieve specified characteristics, but in most cases, the final product is not an ideal design representation. In the case of sailing racing, where hydrofoils are made of composite materials, competitors notice vast differences in the performance of the same products. Differences in performance are significant even within products produced by one manufacturer in one production series. This article addresses the problem of assessing the influence of deviation of the angle of attack on lift-drag characteristics for serially produced hydrofoils. In total, ten hydrofoils were measured. They were produced by one manufacturer for the monotype racing class and are made of carbon fiber composite. The first measurement was done by 3D scanning, and obtained models were analysed in Rhino3D. The parameters of foils and their sections were measured using codes written in the Grasshopper plugin. From a practical point of view, 3D scanning was too time-consuming and expensive to measure a larger number of foils. Therefore, the alternative method for measuring hydrofoil geometry was proposed. Physical measurement was introduced, which allowed testing more foils but was limited to measuring specified parameters. Parameters were chosen arbitrarily and had to be possible to measure on existing foils. During the experiment following quantities were measured: foil span, foil tip coordinates, angle of attack for specified sections, sections’ coordinates (for specified locations defined by foil mounting holes), and sections’ chord lengths. The aim of this article is to show the influence of differences in angles of attack for corresponding sections of hydrofoils on lift and drag characteristics. We began by comparing the foils’ geometry. The first criterion for comparison was the symmetry of both sides of the hydrofoil. Secondly, differences between foils for the same section were compared. Next, ranges and typical deviations of the angle of attack for this population were defined. Characteristics of wings were calculated by performing CFD simulations using OpenFOAM. The finite volume method with steady, turbulent k-w SST flow models was applied. Calculations were performed for scanned hydrofoils and models with a modified angle of attack at particular sections based on previously defined ranges. The calculations allowed defining the influence of changes in the angle of attack on foil lift and drag for the specified magnitude of deviations.