Aerodynamic Interference Effects of Airships
Second International Symposium on Transdisciplinary Fluid Integration, Hyuga, Miyazaki, Japan, October 26-27, 2005
The aerodynamics of airships is dominated by significant interference effects between the flow about the different components of the vehicle. The complex interaction causes nonlinear aerodynamic behaviour of the airship and represents a challenge for theoretical prediction methods. At angle of attack or sideslip free shear layers are separating from the airship hull. The induction of the wake alters the pressure distribution on the hull surface. Due to this interference effect, an aerodynamic lifting force along with induced drag results even for the inclined bare hull without lifting surfaces. A second interference effect stems from the interaction of the empennage with the hull flow. The flow about the stabilizers has a significant impact on the hull loading, increases the aerodynamic lift acting on the fuselage. This increase of the hull lift is known as Lift-Carry-Over. Also the propulsion can change the aerodynamic behaviour of the airship and vice versa. Depending on the position of the thruster, the propulsive efficiency can be increased or decreased by the interaction. Finally, severe ground interference effects appear for small clearances during landing or when the airship is masted. The present paper describes the most important interference effects being relevant for airships in some more detail. To illustrate the effects, experimental and theoretical results will be presented for the LOTTE configuration (Fig. 1), a remotely-controlled solar-powered airship of 16m length which is operated at University of Stuttgart. Detailed wind- and water-tunnel tests, CFD analyses and finally in-flight tests were conducted for this reference configuration during the activities of the airship research group "FOGL" which was funded by the German Research Foundation DFG during 1997 till 2002.