## 3 Results and Discussion
### Flow Field Analysis
When the distance between the leading edge of the airfoil and the ground is small, the change in velocity caused by the change in the shrinkage at the inlet of the flow channel will exceed that caused by the expansion or contraction effect of the flow channel. Figure 11 presents a significant difference in the pressure distribution of the airfoil at a 0\({}^{\circ}\) angle of attack and 4\({}^{\circ}\) angle of attack. Therefore, the trend of aerodynamic coefficient at the 0\({}^{\circ}\) angle of attack is different from that at other angles of attack. Figures 12 and 13 demonstrate the lift coefficient and moment coefficient in a period of different ride heights at 0\({}^{\circ}\) and 4\({}^{\circ}\) angles of attack, respectively. Since the time-averaged value and the fluctuation amplitude of the drag coefficient change little in the range of 0-8\({}^{\circ}\) angle of attack, the drag coefficient will not be discussed. Figure 13 presents that the aerodynamic coefficients of different ride heights have the same trend in a period at a 4\({}^{\circ}\) angle of attack, and the difference is that the position of aerodynamic coefficient curve has moved. The reason is that the ground effect is weaker and weaker with the increase in the ride height, the aerodynamic coefficients are gradually similar to those in the case of free stream, and the fluctuation amplitude is reduced. As can be seen from Figure 12, at a 0\({}^{\circ}\) angle of attack, the trend of the aerodynamic coefficient at the ride height of \(h\)/\(c\) = 0.1 is different from that at other altitudes. With the increase in ride height, the change in shrinkage near the inlet of the flow channel decreases and no longer plays a leading role in the acceleration and deceleration effect of the airflow. Figure 12: The change in the aerodynamics of different ride heights at \(\alpha\) = 0\({}^{\circ}\): (**a**) lift coefficient, (**b**) moment coefficient. \(10^{\circ}\), the fluctuations in the lift coefficient, moment coefficient, and drag coefficient are large, which will cause a deterioration in the WIG craft maneuverability. Therefore, WIG craft should cruise at a moderate angle of attack to avoid flying at small and high angles of attack. The time-averaged aerodynamics in the case of wavy ground is almost the same as those in the case of flat ground. The wavy ground mainly causes a fluctuation in the aerodynamics. Therefore, the trend and fluctuation amplitude of aerodynamics should be paid more attention when airfoils and WIG crafts move over wavy ground at a small ride height. The trend of aerodynamic coefficients at a \(0^{\circ}\) angle of attack and at other angles of attack are different because of its unique flow field structure. The trend of aerodynamic coefficients at other angles of attack is mainly caused by the contraction and expansion of the flow channel under the airfoil, while at 0 degrees of attack there is also the acceleration and deceleration effect of the airflow, caused by the change in the shrinkage of the flow channel. This paper studies the ground effect in the case of wavy ground and analyzes the flow field around the airfoil. All this is of practical significance to the design and safe flight of WIG crafts. [PERSON] and [PERSON] proposed the original idea. [PERSON] performed the numerical simulations and wrote the paper; [PERSON] reviewed the paper and helped to revise it. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors declare no conflict of interest.