Effect of Air Permeability of Ski Jumping Suit Fabric on Stall Characteristics

Abstract

Ski jumping is a sport which competes the flight distance and the flight form. Generally, it is assumed that lower air permeability of ski jumping suit fabric is advantageous for getting more lift. Therefore, one of the regulations for ski jumping competition is that the outstretched fabric should have a medium air permeability of a minimum of 40 L/m²/s at a water pressure of 10 mm Aq. However, the effect of the air permeability of ski jumping suits on aerodynamic characteristics has not been completely clarified yet. The purpose of this study is to investigate the effect of air permeability of jumping suit fabric on aerodynamic characteristics. In the present study, four types of fabric with different air permeability were installed, and the flow behavior around the surface of the fabric clothed elliptic cylinder was investigated by wind tunnel experiments. The stall delay occurred by alterations in the air flow between the inner surface of fabric with higher air permeability and the elliptic cylinder, and the air flows out of the elliptic cylinder surface into the separation region. The stall characteristics for the fabric-clothed elliptic cylinder also vary, depending on the air permeability of the fabric. The higher air permeability improves the stall characteristics.