Over the last two decades, many new branches of hybrid methods with better computational performance have been developed and applied for numerical prediction of separated flow of complex aircraft configurations by researchers as listed in Table 1. The investigation and improvement of the RANS/LES hybrid method have always been the focus of research. Since the 21st century, with the development of the hybrid RANS/LES method, CFD has gradually become a common research tool for stall problems as the hybrid method can greatly improve the simulation accuracy of turbulent flow structures in separation regions without a significant increase in computational resources. Anderson reviewed the primary factors which had affected stall/spin behavior of general aviation aircraft over the history of flight and proposed several prospects for aerodynamic improvements in stall/spin. investigated the poststall characteristics of two rectangular planform wings with leading-edge modifications through a series of low-speed wing tunnel tests. , respectively, to analyze the influence of leading-edge modification on the flow separation state and stall pattern of the wing. Wind tunnel and full-scale flight tests were performed on a general aviation configuration by Johnson et al. A large number of theoretical and experimental investigations of stall and aerodynamic characteristics have been carried out at the end of the 20th century and are very helpful to our research in this paper. In a stall situation, the aerodynamic forces of aircraft show obvious nonlinear characteristics due to the appearance of massive flow separation on the suction side and the flow physics at poststall conditions are not well understood neither by experimental nor computational research until now. Therefore, for business jet, turboprop aircraft, and small civil airplane which are unsuitable for the installation of leading-edge slats, it is particularly important to equip the high-lift configuration with mild-stall characteristics to enhance the flight safety of aircraft. However, their effects are highly dependent on aircraft configuration and must be further validated by a flight test program. In addition to the installation of a slat, aerodynamic accessories such as stall strips, wing fences, and vortex generators can be utilized for improving the local stall behavior without major configuration modifications in the final stages of design. One commonly used approach of delaying wing stall is by installing a well-designed leading-edge slat to effectively lower adverse pressure gradients and suppress separation on the upper side as the angle of attack increases. Stall behavior of aircraft is one of the most important aspects that should be emphasized in the preliminary design stage as it directly affects the safety and maneuverability of aircraft during takeoff and landing. By using the evaluation method, together with design rules summarized from the present study, high-lift configuration with mild-stall characteristic can be obtained in the preliminary stage of design. And through further research, an efficient evaluation method that is capable of qualitatively predicting the stall performance of two-element high-lift configuration by stall angle distribution of wing sections is proposed. Based on the analysis of the calculated results, conclusion can be made that the stall behavior of the configurations is directly related to the onset and evaluation of flow separation on the suction side. Focusing on the low-speed stall and poststall conditions, we investigated the aerodynamic characteristics and flow mechanism of high-lift configuration without slats using an improved delayed detached eddy simulation (IDDES) model which is validated by numerical simulations of the Common Research Model (CRM). In order to simplify the manufacturing process or because of the limitation of the propulsion system, business jet, small civil airplane, and turboprop aircraft are always designed without leading-edge slats, which poses a great challenge to the flight safety during takeoff and landing.
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