The Influence of geometric Simplifications of an Aircraft with Respect to the Optimization of the Aerodynamic Characteristics of the Vertical Tailplane

Kurzfassung

Having as long-term strategy the multi-disciplinary optimization of the vertical tailplane (VTP) of a conventional transport aircraft in mind, some basic studies targeting the aerodynamic analysis were conducted as part of a cooperative project between Airbus and DLR. A first study in this context, which was carried out as part of the AeroNext research project, led to the conclusion, that due to the complexity of the flow around the VTP caused by the flow conditions at the identified design cases and its main geometric characteristics (low aspect ratio and high sweep), at least 3d RANS methods are required to capture all relevant flow-physical effects. Because 3d-RANS-methods are still expensive when considering them as analysis method for a numerical optimization, other ways were sought after to decrease the computational time required for each analysis. Therefore an assessment was carried out to decide whether one would obtain the same optimization result when performing the optimization with the VTP on the complete aircraft geometry compared to an optimization where parts or even everything but the VTP is removed in order to reduce time and cost for mesh generation and flow analysis. This was checked using two different VTP geometries in combination with four different simplification levels of the aircraft. One set of VTP characteristics was derived from each of those simplification levels by calculating different coefficients and gradients for low and high speed flight conditions, believed to be a necessary part of the objective function required for an actual optimization. In order to understand the differences in the VTP characteristics obtained for the different simplification levels, the effects which lead to the changes in the aerodynamic behavior are discussed. The numbers obtained for the two exemplary VTPs alone do not deliver final proof that any considerable simplification will lead to a different optimization result. However, the fact that the differences between the configurations vary in magnitude between the two VTPs, compounded by the very different local flow conditions found on and around the VTP depending on the configurations and onset flow conditions, leads to the conclusion, that it is in general not advisable to heavily simplify the configuration to be optimized unless robust knowledge about the characteristics of the objective function is available in order to avoid detrimental effects on the optimization result obtained.