Modified Target Pressure Distribution for Supersonic Natural Laminar Flow Wing Design

Abstract

Natural laminar flow (NLF) is an important technique for reducing drag of the next-generation supersonic transport aircraft. However, achieving NLF on supersonic transport wings is challenging due to the large swept angles and high-Reynolds-number conditions, which significantly amplify Tollmien–Schlichting (TS) and crossflow (CF) instabilities. To address this problem, this paper proposes a modified target pressure distribution to attenuate the TS and CF instabilities. Compared with conventional targets defined using empirical functions, it is derived in two steps: the first step is to prescribe an initial flat target pressure distribution with a narrow leading-edge flow acceleration region and conduct inverse designs; the second step is to modify the target pressure distribution according to the stability analysis results of the designed wing in order to achieve a balance of disturbance growth at positive and negative wave angles. The proposed approach is validated on a 60°-swept infinite-span wing at Ma=2 and Re=1.39×107. Results demonstrate that TS and CF instabilities are well-suppressed under the modified target pressure distribution, with the transition location delayed from xtr/c=0.26 on the baseline wing to xtr/c=0.95 on the designed wing, suggesting that the proposed method is effective for NLF design on supersonic highly swept wings.