CFD analysis of aerodynamic correlation mechanism in ski jumping takeoff-flight

While previous studies have extensively examined how takeoff and flight techniques affect performance (e.g., jump distance) from a kinematic perspective, few have focused on aerodynamic dynamics, nor the intrinsic relationship between these two phases. Using winter field-measured data, this study identifies key moments during the continuous takeoff-to-flight motion to establish dynamic action phases. It aims to: 1) examine variations in aerodynamic characteristics of the athlete-ski system throughout the entire motion, and 2) through correlation analysis, assess how aerodynamic parameters during both takeoff and flight relate to jump distance and interact with each other. A detailed model of the athlete-ski system was developed in 3D modeling software, incorporating event-specific and anthropometric characteristics. CFD simulations were performed using commercial CFD software. The external flow field was simulated with a turbulence model applying symmetry boundary conditions longitudinally. The Reynolds-Averaged Navier-Stokes (RANS) approach modeled complex external flows over moving interfaces. Real-time climate data such as wind force, speed, direction, temperature, humidity, CO₂ concentration, and atmospheric pressure near the platform were collected. The study focused on the phase from take-off to stable flight, with ten key kinematic instants (M₁～M₁₀) representing a continuous dynamic process. The simulations replicated 24 successful long-distance jumps by eight male athletes from national and provincial teams. Pearson correlation analysis examined relationships between aerodynamic parameters and jump distance during take-off (M₁～M₅) and flight (M₆～M₁₀), and inter-phase connections. The results proved that: 1) The aerodynamic characteristics shifted from drag-dominated during take-off to lift-dominated during the flight phase (M₅～M₁₀), with both the total and ski lift-to-drag ratios exceeding 1 and increasing markedly, indicating significantly improved aerodynamic efficiency; 2) Jump distance showed strong positive correlations with total lift, body moment, and total moment during the late flight phase (M₁₀), while exhibiting negative correlations with drag throughout most of the take-off and mid-to-late flight phases; 3) Significant associations were observed between the aerodynamic parameters of the take-off (M₁～M₅) and flight (M₆～M₁₀) phases, with moderate to strong positive correlations between lift, drag, and moment in mid-to-late take-off (M₃～M₅) and mid-to-late flight (M₇～M₁₀). During the takeoff-to-flight process, the athlete-ski system undergoes a shift from drag-dominated to lift-dominated aerodynamic forces. After leaving the ramp, forward lean and the V-shaped ski technique increase lift while reducing drag, enabling the lift-to-drag ratio to exceed 1 and significantly improving aerodynamic efficiency. Lift and moment positively enhance performance throughout, most notably during stable flight, whereas drag consistently has a suppressive effect. The lift-to-drag ratio plays a key role in stabilizing flight and sustaining glide. Strong correlations were observed between total lift, drag, and moment during takeoff and flight, indicating that positive or negative aerodynamic effects in the takeoff phase propagate into flight. Furthermore, flight aerodynamic parameters can serve as indicators of takeoff technique quality.