# Investigation and Design of the Transonic Laminar Flow Characteristics in a Laminar Aircraft
###### Abstract
The Japanese \"Honda jet\" adopted the NLF wing and NLF fuselage head design and achieved the expected goals and requirements on the first flight in 2003 [12; 13]. Northwestern Polytechnical University developed an \(\mathrm{e}^{\mathrm{N}}\) transition prediction method based on the linear stability theory and studied the infinitely stretched wing and the hybrid laminar wing-body combination [14; 15]. China Aerodynamics Research and Development Center carried out some calibration and application research based on the transition model \(\gamma-\mathrm{Re}_{\theta}\)[16]. Beihang University applied [PERSON] and [PERSON]'s methods, respectively, to the transition prediction of hypersonic flow [17]. A comparison of the two methods for hypersonic boundary layer transition prediction was accomplished via sharp cone at different \(Re\) and HIFiRE-5 shape. Results have proven that both the \(k\)-\(\omega\)-\(\gamma\) transition model and the \"laminar+transition criteria\" model can predict correct transition onsets and lengths at different Reynolds numbers but fail to predict the heat overshoot observed in experimental results. In recent years, the research of NLF technology has been further developed. In 2017, NASA proposed the NLF design method that addressed transition due to attachment line contamination/transition, Gortler vortices, cross-flow and Tollmien-Schlichting modal instabilities [18]. NASA and Boeing also conducted natural laminar flow tests on wings and studied the effect of TS (Tollmien-Schlichting) and cross-flow waves on the transition at different Reynolds numbers based on the common research model in the National Transonic Facility and European Transonic Wind tunnel wind tunnels in the US in 2018 [19; 20]. In 2019, [PERSON] et al. proposed to explain the mechanism by CFPG (examining cross-flow pressure gradient). Their finding suggested that we should pay more attention to the control of CFPG when designing an NLF forward-swept wing towards suppression of cross-flow instability to maintain extensive NLF [21]. At the same time, the effects of the angle of attack and Reynolds number on the Common Research Model with Natural Laminar Flow extent were studied, and the dominant transition mechanism was evaluated at a variety of test conditions by NASA [22]. In 2020, Airbus et al. designed the BLADE (Breakthrough Laminar Demonstrator in Europe) aircraft. The aircraft basis for the experimental aircraft is an A340-300 Flight Test aircraft from which the outer wings were replaced with carefully designed NLF panels of a lower sweep. Additionally, the correlation of data from a range of different test instrumentation provides a comprehensive analysis of the sensitivities of NLF, demonstrating the effectiveness of the BLADE platform [23]. In 2022, experiments with laminar boundary layer suction in adverse pressure gradient were performed on a wing in a wind tunnel. It was proven that applying boundary layer suction can lead to a drag reduction of up to 30% when compared with the no suction condition [24]. In the same year, the wind tunnel and flight tests of a natural laminar flow wing glove were simulated and analyzed by the numerical simulation method considering transition judgment by [PERSON] et al. (2015). It was found that the transition position obtained by numerical simulation in the design stage and the typical non-design state of the wing glove are in good agreement with the flight test results. Therefore, at present, NLF technology is mainly verified by numerical simulation computing and wind tunnel test. Some flight test verification of NLF technology has also been conducted. However, the NLF area of these flight tests is obtained by an NLF wing glove installed on the wing of the aircraft. There are the following shortcomings in this test flight mode. Firstly, the design of the NLF wing glove is subject to the limitations and constraints of the wing itself. The design space is reduced, which affects the diversity of NLF tests.