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Real Flight-Vehicle Effects
The infinitely thin flat plate is the canonical configuration of boundary-layer theory and also of stability and transition research. Basic concepts and fundamental results are gained with and for the boundary-layer flow over it. However, we have seen in Section 7.2 that on real configurations, which first of all have finite length and volume, boundary-layer flow is influenced by a number of effects, which are not present in planar boundary layers on the flat plate. Regarding stability and transition, the situation is similar.
At CAV – and RV-configurations large flow portions exist, which are only weakly three-dimensional, see, e. g., the computed skin-friction line patterns in Figs. 7.8, 7.9, and 9.5. At such configurations appreciable three – dimensionality of the boundary layer is found usually only at blunt noses and leading edges, and at attachment and separation lines, see also [28].
This holds also for possible CAV’s with conical shape and for configurations, where the upper and the side faces are aligned with the free-stream flow (free-stream surfaces), and the lower side is a fully integrated ramp-like lift and propulsion surface, see, e. g., [35]. The lower sides of such, typically slender configurations exhibit more or less parallel flow between the primary attachment lines, Fig. 7.8. This is necessary—for airbreathing vehicles—in order to obtain an optimum inlet onset flow [1]. Of course on axisymmetric configurations at angle of attack and on spinning configurations the attached viscous flow is fully three-dimensional.
In the following sub-sections we discuss shortly—in a descriptive way, in general without giving results of more recent investigations—the influence of the most important real flight-vehicle effects on stability and transition. In Section 8.3 receptivity issues regarding surface and free-stream properties are treated. Other possible real-vehicle effects like noise of the propulsion system transmitted through the airframe and dynamic aeroelastic surface deformations (vibrations, panel flutter) are difficult to assess quantitatively. To comment on them is not possible in the frame of this book.
