CFD Discrete Error Estimation of Low-Aspect-Ratio Flying-Wing Aircraft on Large Attack Angle

The low-aspect-ratio flying-wing (LARFW) is widely used in the design of high-speed aircraft, and it is very important to obtain high-accurate prediction of aerodynamic characteristics. Therefore, how to reduce the discrete error in numerical simulation is always the goal of Computational Fluid Dynamics (CFD), especially at high attack angle. The adjoint equation establishes the relationship between the local residuals and the global discretization error of the objective function, which can directly measure the effect of spatial mesh discretization on the simulation error of aerodynamic characteristics. Based on discrete adjoint theory and hybrid mesh, this paper developed a discrete error estimation and spatial mesh adaptation method, which could quantitatively evaluate the discrete errors caused by spatial grids, correct the errors of aerodynamic characteristics and guide the mesh adaptation optimization, and finally improve the computational accuracy of aerodynamic characteristics of aircraft. Based on the adjoint error estimation method, the spatial discretization error of a LARFW aircraft at a high Angle of attack is studied in this paper. Numerical results show that the discrete errors at the head of aircraft, the leading edge of the wing-body, the separation area at the leeward side, and the high-pressure area of the windward side are very large on high attack angle. From the perspective of flow mechanism, the separated vortices at the wing tip generate and develop at these regions, which have a great influence on aerodynamic characteristics of the LARFW aircraft. Besides, the results in this paper can provide a theoretical support for the grid generation in the numerical simulation of LARFW aircraft at large attack angle.