21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-7.1.1

INVESTIGATION INTO THE FORMATION OF WAVES ON THIN LAYERS OF DE-/ ANTI-ICING FLUIDS ON WINGS

Boelens O. J., Sijp J. C.
University of Twente, The Netherlands

Keywords: formation, waves, de-/ anti-icing fluids, wings

Due to the formation of waves on de-/anti-icing fluids used to protect an aircraft during take-off in winter conditions, the aircraft experiences a lift loss, a drag increase and a decrease of stall angle. The formation of these waves has been investigated by many authors using a temporal stability analysis. In this local analysis, it is assumed that the primary flow is parallel or weakly non-parallel. In case of the flow over a thin layer of liquid, however, the assumption of a parallel primary flow no longer holds. To include the effect of a non-parallel primary flow the analysis employing the one-layer Parabolized Stability Equations(PSE) has been extended to a two-layer analysis. As the PSE method is a spatial type of stability method, the stability characteristics of the flow of a gas over a thin layer of liquid have been investigated also using a local spatial stability analysis. The different modes previously observed in the temporal stability analysis, i.e. the Tollmien-Schlichting mode and the interfacial mode, are also observed in the spatial domain. The interfacial mode, characterized in the temporal domain by small growing rates, is the dominant mode(highest growing rates) in the spatial domain. The results of the local spatial stability analysis have been compared with the results obtained by applying the Gaster transformation to the results of a local temporal stability analysis. For the interfacial mode a modified Gaster transformation is introduced. The evolution of the modes in the streamwise direction has been calculated employing the two-layer PSE method. The effect of the non-parallel primary flow was found to be small. The link to experimental results has been indicated by introducing a growth rate based on the disturbance height of the interface.

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