For distributed propulsion Vertical Take-Off and Landing (VTOL) aircraft, a similarity criterion of aerodynamic characteristics under identical advance ratios is proposed. The advance ratio is employed as a characteristic parameter to describe the aerodynamic/propulsive coupling effect, and an aerodynamic model of the distributed propulsion wing varying with advance ratio is established. The influence of advance ratio on the aerodynamic characteristics of the propulsion wing is then revealed. Wind tunnel and car-top tests are conducted to verify the similarity criterion of aerodynamic characteristics under identical advance ratios, as well as the predictive performance of the proposed model. Results show that the predictions of the aerodynamic/propulsive coupling model exhibit high consistency with experimental data, with the normalized root mean square error not exceeding 10%. The model thereby satisfies the accuracy and real-time requirements of flight dynamics and flight control systems simulation, providing theoretical support for modeling approaches of distributed propulsion VTOL aircraft.

Distributed Propulsion Wing (DPW) technology offers significant advantages in terms of flight energy savings, but the strong aerodynamic coupling between the propulsive internal flow and aerodynamic external flow brings significant design challenges. As the primary DPW profile design is of great significance, this paper proposes a hybrid method to solve the inverse problem mainly based on the formula relationship between the required aerodynamic loads and the profile shape, which is more direct and instructive compared with traditional parametric iterative methods. The aerodynamic characteristics are described by the circulation distribution in the Fourier series form, then the mean camber line of the profile is solved through the re-derived airfoil theory considering disk’s influence. Further CFD correction methods are also proposed. To validate the effectiveness and feasibility of the proposed hybrid inverse method, several DPW profile design tests are then conducted. Finally, the relationship between 2D and realistic 3D unit shape is also researched. The results show that the proposed inverse design method has great accuracy and convergence speed in the design tests, and shows good robustness against changes of the design parameters. The 2D profile shape and the actual 3D shape of DPW unit can establish an aerodynamic-propulsion equivalent relationship based on the same internal mass fluxes.

This paper proposes a propulsion/aerodynamic coupling model for the distributed-propulsion-wing with induced wing configuration based on the research on distributed-propulsion vertical takeoff and landing vehicles, combined theoretical models and engineering assumptions. This model enables real-time and rapid calculation of the aerodynamic performance of distributed-propulsion-wing with induced wing configuration within the entire flight envelope, including vertical takeoff, transition, and cruise phases. Firstly, a fast calculation method for ducted jet velocity is developed by combining the ducted flow field model and the ducted thrust enhancement coefficient. Then, based on the momentum theory, the propulsion-aerodynamic coupling model is derived for both powered and unpowered conditions. Finally, the characteristics of the propulsion-aerodynamic coupling model are analyzed, and CFD simulations and analyses conducted for typical flight conditions. The results show that the proposed propulsion/aerodynamic coupling model for the distributed-propulsion-wing with induced wing configuration exhibits high accuracy and fast computation speed, meeting the real-time calculation requirements for dynamic system analysis and flight control system design.

The influence of chord length and position on the design results of the Distribution-Propulsion-Wing (DPW) is compared at the same target lift and pitching moment, based on a two-dimensional inverse design method of the DPW aiming at chordwise circulation distribution. Additionally, the two-dimensional shape optimization design of the DPW is conducted to achieve minimum drag, minimum total pressure loss and minimum velocity distribution distortion of the disk inlet. The results show that the average relative error between the distribution of the chordwise circulation and the target value is 0.058 7 in the inverse design test. In the analysis of the duct parameter influence, a fixed chord length of the upper duct wall and a forward chord position, or a fixed trail edge position of the duct wall and a longer chord length lead to a lower surface drag and a higher lift coefficient slope, while the pitch moment slope changes from negative to positive as the angle of attack changes. After the optimization, the position of the two-dimensional DPW duct wall moves forward, the drag coefficient decreases by 160%, the total pressure of the disk inflow basically does not lose, and the velocity distribution uniformity is further increased.