Measurements and simulations are presented of the flow past a tailplane research airfoil which is designed to show a mixed leading-edge trailing-edge stall behaviour. The numerical simulations were carried out with two flow solvers that introduce transition prediction based on linear stability theory to RANS simulations for cases involving laminar separation bubbles. One of the methods computes transition locations across laminar separation bubbles whereas the other assumes transition onset where laminar separations occur. For validation of the numerical methods an extensive measurement campaign has been carried out. It is shown, that the methodology mentioned first can simulate the size of laminar separation bubbles for angles of attack up to where the separation bubble and the turbulent separation at the trailing edge are well behaved and steady in the mean. With trailing edge separation involved, the success of the new numerical procedure relies on the diligent choice of a turbulence model. Finally, for flows with increased unsteady behaviour of both, separation bubble and turbulent separation, which were observed at higher angles of attack in the experiment between maximum lift and leading-edge stall, steady state prediction methods for transition can no longer be applied and time-accurate methods have to be developed in a further step.

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A generic wind tunnel model for tailplane stall investigations was designed to establish an experimental database for code validation. The configuration is numerically optimised to obtain large Reynolds numbers at the horizontal tailplane in a wind tunnel of limited size. It consists of a fuselage, a detachable horizontal stabiliser and a tip-truncated wing, that mounts the model at the turntables of the closed test section. Fuselage and wing are used to create representative downwash conditions in the tailplane region inside the wind tunnel, compared to free-flight. The tests were conducted at a freestream Mach number of 0.16 and at a Reynolds number based upon the mean tailplane chord of 0.72 • 10 6. Tailplane stall with natural and fixed transition is visualised by tufts and oil-flow. In case of natural transition, pressure measurements and Particle Image Velocimetry in the area of turbulent trailing-edge separation provide qualitative data for the validation of numerical simulation approaches. First numerical simulations, using an unstructured Reynolds-averaged Navier Stokes Code, are in good agreement with the experiments. They show a separation of the boundary layer starting at the trailing edge with high crossflow velocities at the outer tailplane. Depending on the boundary-layer transition, the stall occurs abruptly for natural transition, initialised by a burst of a laminar separation bubble, or gradually for fixed transition. A deflected elevator shifts flow separation towards lower incidence angles of the tailplane without changing the process of flow separation.

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