# Research on the Aerodynamic-Propulsion Coupling Characteristics of a Distributed Propulsion System
## 1 Introduction  
Due to the severe problems of air pollution and excessive consumption of fossil fuels caused by the rapid development of the aviation industry, an increasing number of countries are advocating for the development plan of \"Green Aviation\". The National Aeronautics and Space Administration (NASA) of the United States has proposed the N + 3 development goal, requiring a 70% reduction in aircraft fuel consumption by 2030 [1, 2, 3]. However, it is difficult to meet the future requirements of aircraft in terms of energy conservation and emissions reduction merely by relying on existing technologies to improve traditional aircraft. Distributed electrical propulsion (DEP) has attracted much attention from scholars due to its advantages of low emissions, low consumption, and low noise [4, 5, 6, 7]. DEP aircraft have become a research hotspot among scholars due to its favorable economic performance and propulsion advantages. [PERSON] [8] and [PERSON] [9] provided detailedintroductions to distributed propulsion aircraft with different configurations and elucidated their potential aerodynamic--propulsion advantages. [PERSON] [10] and [PERSON] [11] conducted research on the aerodynamic-propulsion coupling characteristics of the DEP system through low-speed wind tunnel tests, revealing the potential benefits of this coupled layout for aerodynamic-propulsion interaction. [PERSON] [12] explored the influence of engine flow rate and the engine installation position on the aerodynamic performance of the blended wing body aircraft. [PERSON] [13] conducted research on the aerodynamic influence law and flow mechanism of the DEP system with the boundary layer ingestion (BLI) effect based on the two-dimensional calculation method and considering the influence of multiple variables. [PERSON] [14] revealed the influence law of the internal and external flow coupling effect on the aerodynamic performance and flow mechanism of the DEP system under different flight conditions. [PERSON] [15] analyzed the coupling interference mechanism and law among ducted fans in the DEP system by combining experiments and numerical simulations. [PERSON] [16] investigated the effects of different configurations, such as an isolated ducted fan layout, a single ducted fan and wing coupled layout, and a multi-ducted fan and wing coupled layout, on the performance of a single ducted fan through wind tunnel tests. The research showed that the coupling interference between the fan and the wing significantly disturbs the internal flow of the ducted fan, thus resulting in performance losses. [PERSON] [17] and [PERSON] [18], respectively, carried out numerical studies on distributed ducted fans, focusing on the influence of the internal and external flow coupling effect on the aerodynamic performance of the coupled configuration. The above research results indicate that there is a significant coupling effect between aerodynamics and propulsion in the DEP system. Although many scholars at home and abroad have carried out research on the complex interactive coupling mechanism and aerodynamic-propulsion characteristics of the DEP system, few have paid attention to the influence law of the internal and external flow coupling effect on the performance of ducted fans, especially the influence of boundary layer ingestion on the intake distortion of ducted fans, as well as the relevant details of the flow field. Therefore, this paper develops a body force model (BFM) which is capable of conducting rapid numerical simulations and calculations for complex rotating turbomachinery. And this model is applied to carry out numerical simulation research on an over-wing symmetric configuration with five distributed ducted fans. The influence of the internal and external flow coupling effect on the aerodynamic characteristics of the coupled configuration and the performance of the ducted fans is deeply explored.