Interface Characteristics and Drag Reduction Performance of Skis Based on Air-Snow Two-Phase Flow Simulation

In the game of skiing, the factors, which affects the results of the competitive sport include not only the athlete's own skills and environment, but also the interaction between snowboard and snow which is limited by the structure and posture of snowboards. There are few literature focusing on the interaction among snowboard air fluid and snow flow. At present, researchers are mainly engaged in snowboard design principle and method, considering the interface interaction mechanism between ski and snow. The interface between snowboard and snow has the coupling effect between snow, air and snowboard at the same time. The interaction time is short, so it is very difficult to be investigated by conventional experimental methods.　In this paper, the CFD simulation was carried out at the macro scale, ignoring the interaction between snow particles and skis. The traditional CFD simulation method was adopted to take air and snow as two different fluids (mixed fluids). The movement of two-phase fluid, one according to the air parameter settings, the other according to the snow parameter settings, was depended by the skis structure and posture. According to the competition equipment rules of the International Ski Federation, the structural parameters of the snowboard were selected for the design process.　The structural optimization design of snowboards involved four parameter variables, and each parameter has three different values. For the design of single factor, the total number of CFD simulation reached 3⁴=81. So the orthogonal experimental design method was adopted. Orthogonal experimental design method was a method to arrange and analyze multi-factor test by using orthogonal table. The experiment considered the effect of four parameters on the joint force of skis, and did not consider the interaction between various factors L₉ (3⁴) orthogonal table was selected, so nine models and nine tests can find out the best design of snowboard and the biggest influencing factors. The results showed that the edge chord length was the most influential factor among the four factors. At the same time, the optimal combination of the four factors was found that the minimum width of the side edge was 230.5 mm, the chord length of the side edge was 1 050 mm, the arch height of the body was 4.5 mm, the warping height of the head was 56 mm and the warping height of the tail was 46.5 mm. The minimum resultant force on interface between the snowboard and snow was 13.64 N, compared with 17.34 N of the original design of snowboard.　Skiing pose was a comprehensive concept, including the position of knee, hip, back, arms and other body parts as well as ski pose. The angle of attack pose of snowboard directly affected the air mixing state of the sliding interface, and thus indirectly affected the resultant force of the interface. According to the optimal combination of attack angle optimization simulation on snowboard, when the angle of attack of the snowboard was about 5°, air flow state was better. This was the optimal choice, which can play a guiding role in the process of movement of an athlete.