# Experimental Study on the Effect of Wind Speed on Hail Impacts
## 3 Experimental Analysis and Results  
### Investigating the Influence of Wind Speed on Hail Impact Force Dynamics  
In this experiment, with wind speed as the variable, 3.2 cm diameter hailstone particles were selected as test objects to investigate the time-history curve of the impact force during vertical impacts (90\({}^{\circ}\) angle of attack) on a metal force-measuring panel at a velocity of 26 m/s. The experimental results are shown in Figure 4. \begin{table}
\begin{tabular}{c c c} \hline
**Hail Diameter (cm)** & **Hail Mass (g)** & **Theoretical Velocity (m/s)** \\ \hline
2.40 & 6.35 & 22.04 \\
2.80 & 10.12 & 23.47 \\
3.20 & 15.22 & 24.79 \\ \hline \end{tabular}
\end{table} 
Table 2: Determination of the theoretical velocity of hailstones. Figure 4: Time-course curves of hailstone impact forces under different wind speeds. \begin{table}
\begin{tabular}{c c c} \hline
**Hail Diameter (cm)** & **Hail Launch Velocity (m/s)** & **Wind Velocity (m/s)** \\ \hline
2.40 & 17/20/23 & 0/5/9/11 \\
2.80 & 20/23/26 & 0/5/9/11 \\
3.20 & 23/26/29 & 0/5/9/11 \\ \hline \end{tabular}
\end{table} 
Table 3: Experimental conditions. As shown in Figure 4, during the impact tests, although the total duration of hailstone impacts showed no significant variation with changing wind speeds, the time required to reach the peak impact force decreased progressively as the wind speed increased, while the peak impact force magnitude rose substantially. At a wind speed of 13 m/s, the peak impact force of the hailstones reached its maximum value, exhibiting an increase of approximately 18.9% compared to the windless condition (0 m/s). The reason for this phenomenon was hypothesized to be based on the theory of hydrodynamics: when wind interacts with spherical hailstones, the resulting aerodynamic forces arise from the superposition of pressure and tangential shear stresses acting on the hailstone interface. These forces can be decomposed into streamwise (axial) and transverse (normal) components relative to the incoming direction. The transverse component consists of lift and downward pressure and is determined by the pressure gradient around the surface of the hailstones. For vertically descending hailstones, downforce is greater than lift due to asymmetric flow separation and unfavorable pressure gradients in the windward hemisphere. This downward net lateral force amplifies the vertical impact force through momentum transfer. These findings demonstrate that wind speed is an indispensable parameter for evaluating the damage potential of hailstorms. Hailstones driven by strong winds exhibit significantly enhanced destructive capacity. Ignoring wind effects and considering only hail impacts in isolation would lead to an overestimation of structural impact resistance, thereby compromising the accuracy of risk assessments for wind-hail disasters. Study on the Effects of Wind Speed on Hail Impact Force Variation Patterns Across Different Diameters  
To further investigate the coupling mechanisms between wind speed and hailstones of varying diameters, this study analyzed the time-history curves of impact forces for three hailstone diameters (2.4 cm, 2.8 cm, and 3.2 cm) at a constant launch velocity of 23 m/s under different wind speeds, as illustrated in Figure 5. As shown in Figure 5, the impact force-time curves for all hailstone diameters exhibit a pulsed shape, with short impact durations concentrated between 0 s and 0.0025 s. Due to the limited variation in hailstone diameters, the influence of wind speed on impact duration was negligible at 0 m/s. However, with increasing wind speeds, smaller diameter hailstones reached peak forces earlier and exhibited shorter interaction times. This indicates that wind exerts distinct effects on hailstones of different sizes. Figure 5: Impact force–time-course curves under simultaneous variations in wind speed and hailstone diameter. Peak hail impact is the value of the maximum impact force produced instantaneously by hail when it strikes the surface of an object.