Attached High-Speed Viscous Flow
At the beginning of Chapter 6 we have noted that in the hypersonic flight regime, like in the lower speed flight regimes, flow fields can be separated into inviscid and viscous portions. At high altitudes this separation may become questionable. However, the central topic of this chapter is attached highspeed viscous flow, whose basic properties are described with the help of the phenomenological model “boundary layer”.
We look first at the typical phenomena arising in viscous flows and their consequences for the aerothermodynamic vehicle design. Attached viscous flow is characterized, in general, by the molecular transport of momentum, energy and mass, Chapter 4, towards the vehicle surface, with wall-shear stress, the thermal state of the surface, thermo-chemical wall phenomena, etc., as consequences. We treat the boundary-layer equations, consider their limits in hypersonic flow, examine the implications of radiation cooling of vehicle surfaces, and define integral properties and surface parameters, including viscous thermal-surface effects. (Examples of viscous thermal surface effects were given in some of the preceding chapters. More are collected and discussed in Chapter 10.)
Finally we give simple relations for laminar and turbulent flow—with extensions to compressible flow by means of the reference temperature/enthalpy concept—for the estimation of boundary-layer thicknesses, wall-shear stress, and the thermal state of a surface (wall heat flux and wall temperature) for planar surfaces, spherical noses and cylindrical swept edges. A case study closes the chapter.
Laminar-turbulent transition and turbulence in attached viscous flow, which we have to cope with at altitudes below approximately 40 to 60 km, are considered in Chapter 8. We discuss there the basic phenomena, their dependence on flow and surface parameters, and on the thermal state of the surface. The state of the art regarding transition prediction and turbulence models is also reviewed.
(C Springer International Publishing Switzerland 2015 E. H. Hirschel, Basics of Aerothermodynamics,
DOI: 10.1007/978-3-319-14373-6 _7
Connected too to viscous flow are the flow-separation phenomenon and other strong-interaction phenomena. In Chapter 9 we treat separation and the typical supersonic and hypersonic strong interaction phenomena including hypersonic viscous interaction, and finally rarefaction effects, which are related to the latter phenomenon. All these phenomena are of large importance in aerothermodynamic design, because they may influence not only performance, flyability and controllability of a flight vehicle, but also, and that very strongly, the thermal and mechanical loads on the airframe and its components.