| The trans-media aircraft is a new amphibious equipment which can fly in the air and dive underwater,and has the advantages of strong maneuverability,wide combat range and good mission accessibility.Its amphibious application requires that both aerodynamic characteristics and water entry characteristics should be considered in the layout design.Among them,the water entry of trans-media aircraft is a complex multi-phase flow problem involving attitude changes,coupling between the aircraft,air and water,and sudden load changes when crossing the gas-liquid interface.The main purpose of this study is to understand change law of forces on aircraft in the process of flying in the air and entering water,and study the influence of different conditions on the forces of aircraft,so as to provide theoretical basis for the development of trans-media aircraft.In this thesis,the computational fluid dynamics software STAR-CCM+ is used to solve the three-dimensional Reynolds average N-S equation and use the SST k-?turbulence model to simulate turbulent flow.Different grid distribution strategies are used to calculate the flow fields of the three aircraft configurations.The aerodynamic difference of the three aircraft configurations in the air is analyzed and co mpared with the wind tunnel test results,which verifies the feasibility of the numerical simulation method and calculation model used in this thesis.Based on the aerodynamic characteristics of the aircraft in the air,the overset grid techniques are used to simulate the different altitudes of the aircraft from the water surface,and the VOF method is used to simulate the interaction of the aircraft with the water surface.The aerodynamic differences between the optimized configuration and the deformed-wing configuration at the approach and entry of water are analyzed and their effects on the flight stability of the aircraft are estimated.The following conclusions are obtained: the deformed-wing configuration has little change in pitch moment coefficient compared to the optimized configuration before entering the water,which can ensure the aircraft to maintain a stable longitudinal moment;The aerodynamic forces have sudden changes with more than one order of magnitude during water entry for both the deformed-wing and optimized configurations.For the deformed-wing configuration,the absolute value of the negative lift coefficient increases and the drag coefficient increases,while the pitch moment coefficient does not change much,which keeps the better longitudinal stability.And the deformed-wing increases the transverse stability at the same time.Therefore,it is necessary to carry out the wing variant when the aircraft enters the water.The calculation method and grid generation method used in this thesis can be used for unsteady calculation of aircraft entering water in the future,and also can be applied to simulate other related fields. |
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