Natural laminar flow wing design method for supersonic civil aircraft considering full-aircraft sonic-boom characteristics

Low drag and low sonic-boom design technologies both play significant roles in the re-introduction and sustainable commercial operations of next-generation supersonic civil aircraft. Although the potential of natural laminar flow wing to reduce the drag of supersonic civil aircraft has been verified, further research is still needed to achieve laminar flow wing design under the constraint of low sonic-boom intensity. Considering that the laminar flow region of the wing is determined by the wing pressure distribution, the influence of wing pressure distribution on the sonic-boom characteristics of the aircraft is first investigated. A method for supersonic natural laminar flow wing design considering low sonic-boom intensity requirement of the aircraft is then proposed. Firstly, the influence of wing pressure distribution on the equivalent areas and sonic-boom waveform of the aircraft is analyzed. Results indicate that on the low-boom configuration, changing the wing pressure distribution mainly leads to changes in the distribution of axial lift of the aircraft. In addition, the original configuration's shock-expansion waves that feature low-sonic boom characteristics are also affected, leading to increase of intensity of ground sonic boom. Based on these discoveries, a three-step method for supersonic natural laminar flow wing design is proposed considering the sonic-boom constraint of the aircraft. The first step is to conduct low boom design to determine the layout of the configuration and fuselage shape. The second step is to conduct multiple rounds of pressure gradient inverse design on the wing to obtain the pressure distribution required by natural laminar flow. The third step is to carry out multiple rounds of low sonic-boom design on the fuselage, horizontal tail and vertical tail to compensate for changes in sonic boom characteristics caused by changes in wing pressure distribution. The proposed method is applied to achieve natural laminar flow on a wing of a 30 t low boom supersonic civil aircraft configuration. The designed configuration not only maintains low sonic-boom characteristics (sonic boom intensity equals 81.7 PLdB), but also achieves 33% natural laminar flow on the upper surface of the wing and a 5.2% reduction in friction drag compared to the baseline configuration. The results verify the effectiveness of the proposed method.