Engineering calculation method of viscous force for air-breathing hypersonic vehicle

Viscous interference has an important influence on aerodynamic, propulsion and flight stability of the air-breathing hypersonic vehicle. The calculation precision based on inviscid theory cannot meet the actual engineering needs. In the work, the viscous force engineering estimating method was researched for the airbreathing hypersonic vehicle, which has an airframe/propulsion integration characteristics and is different from the conventional vehicle. First the properties of the flow was determined by using two-dimensional shock expansion theory and one dimensional flow model. Then viscousforce coefficients were calculated. Finally, viscous forces were obtained by integrating viscous force coefficients for vehicle. By calculating the viscous force on the vehicle surface and inside scramjet engine, the viscous effects on aerodynamic were analyzed and the law of viscous force varying with flying height was obtained. Result shows that the viscous effects are prominent, especially for drag force characteristic, viscous drag force accounts for 78% of total drag force. To validate the engineering method, a certain air-breathing hypersonic vehicle inlet was computed and the results were compared with CFD results. This method can be applied to analysis of viscous effect and rapid calculation of viscous force in aircraft conceptual design and preliminary research stage.