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SUMMARYThis paper details a multigrid-accelerated cut-cell non-conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow. This is done via a single equation set that describes sub-, trans-, and supersonic flows. Cut-cell technology is developed to furnish body-fitted meshes with an overlapping mesh as starting point, and in a manner which is insensitive to surface definition inconsistencies. Spatial discretization is effected via an edge-based vertex-centred finite volume method. An alternative dual-mesh construction strategy, similar to the cell-centred method, is developed. Incompressibility is dealt with via an artificial compressibility algorithm, and stabilization achieved with artificial dissipation. In compressible flow, shocks are captured via pressure switch-activated upwinding. The solution process is accelerated with full approximation storage (FAS) multigrid where coarse meshes are generated automatically via a volume agglomeration methodology. This is the first time that the proposed discretization and solution methods are employed to solve a single compressible-incompressible equation set on cut-cell Cartesian meshes. The developed technology is validated by numerical experiments. The standard discretization and alternative methods were found equivalent in accuracy and computational cost. The multigrid implementation achieved decreases in CPU time of up to one order of magnitude.

A five-degree-of-freedom dynamic wind-tunnel rig is used in the observation of large-amplitude, stall-related and self-sustaining, pitch oscillations of a model aircraft. These oscillations are investigated on the dynamic wind-tunnel rig during a quasi-steady ramp input to the aircraft model's elevator surfaces in one-degree-of-freedom pitch mode and in the longitudinal two-degree-of-freedom pitch and heave modes. A mathematical model of the aerodynamics, incorporating the effects of dynamic stall, is proposed. The aerodynamic model is coupled to the test rig equations of motion, which include terms for joint friction, and its parameters are fitted to the experimental data. This latter process is achieved using continuation and bifurcation analysis, which also helped to reveal the influence of friction forces on the oscillatory behavior. The quality of the fit and the use of a phenomenological model allow a possible cause for these oscillations to be proposed.

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