Dynamic stability analysis of a propeller-wing wind tunnel model

Kurzfassung

The research project “Bürgernahes Flugzeug” deals with the configuration of a future airplane with the properties of short take-off and landing and with reduced noise from the acoustic aspect. These properties should permit flight from a smaller airport closer to a city. In this project, under the cooperation of the main research partners: University of Braunschweig, German Aerospace Center (DLR) and University of Hannover, a wind tunnel model for the mainly aerodynamic and acoustic investigations was designed. In 2012, this model will be utilized in low speed German-Dutch wind tunnel (DNW-NWB) in Braunschweig for different research activities and measurements. Occurrence of any kind of dynamic instability during the wind tunnel test will cause lots of cost and loss of time. Even it is possible to have the situation that the model is stable and no dynamic instability occurs but the oscillation of the model is not desirable. An undesirable oscillation of the model would have cross effects on the aerodynamics and acoustics of the model and therefore would have effect on measurements. To prevent all the well known dynamic problems during the wind tunnel test, performing dynamic stability analysis in both design stage and after the construction the model is an inevitable task. This paper gives a review of aeroelastic analysis of the designed wind tunnel model under the predefined wind tunnel test conditions. Wing flutter is one of the dynamic instability phenomena that should be prevented from occurring. In general, movement/oscillation of a wing due to its elasticity induces aerodynamic forces/moments. Depending on the structure of the wing, these originated forces and moments could make the wing to oscillate with increasing amplitude (Flutter). For a propeller-wing system with rotating propeller, gyroscopic effect of the propeller could change the dynamic behavior of the whole system (comparing to a model with non rotating propeller). This effect should be also considered for the flutter analysis. Another dynamic instability, which can happen for this model is “whirl flutter”. Whirl flutter is a self induced dynamic instability, which originates from the propeller. In general, gyroscopic and aerodynamic coupling effects of the propeller create a so called whirl mode on the propeller. Again, depending on the structure of the model, wind and rotor rotation velocity an unstable whirl movement of the propeller head (hub) can occur. In this work, the occurrence of two aforementioned dynamic instabilities of the wind tunnel model with the usage of different simulation tools was investigated. Analysis performed includes: (a) - wing flutter analysis with the consideration of the propeller gyroscopic effect and its motion induced forces/moments (b) - propeller-nacelle-wing whirl flutter analysis with the consideration of the wing elasticity and aerodynamics.