Abstract: The integrated design of fuselage and nozzle after-body structure is particularly important in improving the lateral and backward stealth performance of high stealth UAV. However, the design also brings new challenges in fields of aerodynamics, structure and strength. The prediction of aerodynamic load under the effect of jet is one of the key problems. Therefore, based on the CFD method and wind tunnel test data, the steady and dynamic aerodynamic loads and their influence laws of high stealth UAV nozzle and after-body structure are studied. The main conclusions are as follows:the complex wave system formed by the jet projected onto the after-body wall will form the aerodynamic loads of alternating pressure and suction, which are rather sensitive to the nozzle pressure ratio. A small pressure ration change may lead to the change of lad direction, and the steady-state aerodynamic load distribution is also affected by the inflow velocity and the secondary/mainstream flow ratio. The numerical calculation based on IDDES method also has good prediction accuracy for dynamic aerodynamic load. The flow field is divided into several regions, such as the mixing region of jet mainstream and secondary flow, the core region of jet, the mixing region of jet mainstream and secondary flow, the core region of jet, the mixing region of jet and outer-flow, which is helpful to reveal the distribution law of fluctuating pressure from the flow mechanism, and has been verified by experiments. The results show that the extreme region of dynamic load is located at the boundary of jet region, where the shear mixing is the strongest. While, in the core region of the jet, although the steady aerodynamic load is strong, the dynamic aerodynamic load is relatively low.

Key words: jet, after-body, load, UAV, aerodynamic