Computational model of high altitude aircraft aerodynamics

The paper presents computational fluid dynamics hybrid model for analysis of complex flow composed of flow zones at low Reynolds number and flow zones at relatively high Reynolds number conditions. In the described model both ranges of the flow are separated and resolved independently using different way of simulation. That kind of phenomenon is typical for aerodynamics of unmanned propeller driven aircrafts operating at very high altitude conditions (stratospheric). That type of aerial vehicles is now used for military and scientific purposes. In many cases, the wings of a plane are operating at relatively high Reynolds number flow conditions and low angles of attack while the parts of the propeller blades are working at low Reynolds number flow condition and high angles of attack. Described numerical model was used for analysis of the impact of working propellers on the aerodynamics of the aircraft. Analysis was made on the example of a twin-engine, unmanned aircraft with electric motors during the high altitude flight. Three configurations were studied and compared: the plane without propellers, the plane with pusher propellers and the plane with tractor propellers. For each configuration, distributions of aerodynamic coefficients along the span of the wing and their global values for the entire aircraft were estimated. Calculations were performed using the Fluent solver with implementation of a model of propeller based on the Blade Element Theory. Results of the analysis indicate a slight advantage of the tractor propellers configuration.