This paper studies the quadcopter’s mutual interference phenomenon. The flow field of the quadcopter at different flight speeds is simulated by solving the three-dimensional unsteady Reynolds averaged Navier-Stokes equations with sliding mesh methods. “Virtual Modes” (VMs) are introduced to examine the mechanisms of aerodynamic interference among the quadcopter’s components (front rotors, rear rotors, and fuselage). By comparing the aerodynamic forces of different VMs, this work shows that mutual interference to the front rotors can be negligible, interference to the rear rotors is due to the wake of front rotors and fuselage, and mutual interference to fuselage is caused by front and rear rotors. Only the rear rotors’ thrust and pitch moment as well as the lift of the fuselage are significant. At the flight speed of 5–15 m/s, the mutual interference causes 11% loss of thrust and 35% loss of pitching moment to the rear rotors; In the cases of hovering and 25 m/s forward flight, the interference is negligible.
This paper presents a power-based analysis through 3D Reynolds-averaged Navier–Stokes simulations for a typical transonic transport aircraft resented by the DLR-F6 model. Two configurations were employed in CFD simulations. The original F6 model geometry was defined as the wing body configuration, and a wake-filling actuator disc was added to the F6 model to establish the BLI configuration. This study proposes a segregated 3D computational domain in RANS simulations to track the change in power terms in the flow field so that the power conversion process can be studied and visualized. For the wing body configuration, the power-based analysis illustrated the power conversion process, showing that about 35% of the total power input remains in the form of the mechanical power of aircraft wake at the outlet plane. For the BLI configuration, 22% of the total power input was left in the form of the mechanical power of downstream flow mixed with the wake and jet at the outlet plane. This study elaborates on the error of the mechanical power imbalance, showing that the convergence in aircraft drag does not necessarily lead to a small error in 3D RANS simulations. The high value of power imbalance error is associated with the wing.
The flow-induced vibration characteristic of the U-section rubber outer windshield structure of high-speed train is the key factor to limit its high-speed movement. Accurate and effective flow-induced vibration analysis of windshield structures is an important topic. In this paper, a hybrid modeling method for the analysis of flow-induced vibration of windshield structure is innovatively proposed for the U-section rubber windshield system of high-speed train. The method uses the external aerodynamic load obtained by aerodynamic simulation as the input condition of the flow-induced vibration model, and maps the aerodynamic load to the structural dynamics model characterized by the modal test data of the windshield structure. The flow-induced vibration model is established by means of modal superposition method and the time-domain response is effectively integrated by Runge Kutta method with variable step size. The results show that this method can effectively simulate the flow induced vibration of the wind baffle structure, and the real-time relationship between the aerodynamic load and the modal characteristics of the structure and the response of displacement and velocity can be obtained. On this basis, the comprehensive dynamic performance of the windshield system of high-speed trains at 400 km/h under external aerodynamic load is studied, that is, the force, displacement and velocity variation rules of the flexible structure are examined. It is determined that the displacement and velocity response curve of the measuring point near the lower side of the U-section rubber outer windshield is significantly higher than that of other parts. Moreover, the contribution of the first mode to the dynamic response of the structure is very obvious. This method provides an efficient calculation method for analyzing the flow-induced vibration characteristics of complex flexible structures.
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