Design Optimization of a WIG Craft’s High Lift Device Considering Ground Effect

The WIG (Wing-in-Ground) craft is a novel vehicle that makes use of the ground effect to realize cruising above the water. Contrary to the lift increase when a single wing in proximity of the ground at low angles of attack, the high lift device will experience a decrease in lift when in proximity of the ground, resulting in poor lift enhance when the high lift device is designed without considering ground effect, making it difficult to meet the takeoff requirements of low angles of attack, low speeds, and low flying heights for WIG crafts. In order to improve the lift increasing effect of the high lift device under low altitude conditions, this paper proposes a design optimization method for the high lift device of WIG crafts considering ground effect, which is based ona surrogate-based optimizer, a high lift device with significant lift increase was obtained at low altitudes. Firstly, based on the RANS solver, the aerodynamic performance of a two element high lift device designed without considering ground effect was evaluated. It was found that the high lift device would exhibit severe flow separation on the upper surface of the flap when in proximity of the ground, resulting in a significant reduction in lift of the high lift device. Therefore, it is not suitable for the WIG crafts that operate in the ground effect zone throughout the entire take off process. To address the above issues, with the abovementioned high lift device (designed without considering ground effect) as baseline, a design optimization for a high lift device considering ground effect is carried out, the results showed that the designed high lift device considering ground effect did not encounter flow separation when in proximity of the ground, resulting in a significant increase in takeoff lift by 26.6%. Further, targeting the high takeoff lift requirement of a certain WIG craft, taking the shape of flap’s front slit, shape of flap’s back slit, flap deflection angle and flap hinge position as design variables, an design optimization of the high lift device considering ground effect was carried out. The designed high lift device increased the take off lift by 34.7%. The WIG craft mounted with the designed high lift device resulted in an increase in takeoff lift from 10.3 tons to 11.1 tons tons, which makes an increase of 7.8%.The design optimization results verified the effectiveness of the method developed in this paper.