Examples in Foregoing Chapters

In the next sections several examples of viscous thermal surface effects are discussed. Before that is done, examples mentioned and/or discussed in pre­vious chapters are recalled.

— The thermal reversal during low-speed flight after the re-entry of the Space Shuttle Orbiter is mentioned at the end of Section 3.1. Thermal reversal means that the wall has a temperature, which is larger than the recovery temperature belonging to the momentary flight Mach number. The result is that the skin-friction drag is smaller than at a cold wall, which is given in wind-tunnel experiments for the creation of the low-speed aerodynamic data set. This possibly is the reason for the observation during the re-entry first flight of the Orbiter that the lift-to-drag ratio in the low supersonic and subsonic flight phases was larger than predicted. However, because of the thicker boundary layer the pressure (form) drag of the wing will increase [3]. This may change the conclusion.

— The influence of the temperature gradient in the gas at the wall and the wall temperature itself on the point-of-inflection behavior of the tangential flow profile of the boundary layer is discussed in Sub-Section 7.1.5, see also the previous section of this chapter.

— Properties of attached viscous flow as they are influenced by the wall temperature are considered in Section 7.2 with the help of the reference – temperature concept. Some of the results are summarized in the previous section.

— In Section 7.3 results of a numerical study of the flow past the forebody of the lower stage of the TSTO space transportation system SANGER are presented. Different assumptions regarding the gas model (perfect gas, equilibrium real gas) and surface radiation cooling (off: є = 0, effective: є = 0.85) influence the skin friction distribution as shown for the lower symmetry line. The general result is that the hotter the surface, the smaller is the skin friction. The effect is mainly seen for turbulent flow, much less for laminar flow, as summarized in the previous sub-chapter, too.

— The influence of the thermal state on the surface on the stability behavior is discussed in Sub-section 8.1.4. A numerical example shows the influence of the wall temperature—smaller or larger than the recovery temperature— on the amplification rates of the first and second mode in the boundary layer at a blunt cone at M= 8. Another numerical example shows for different free-stream Mach numbers the influence of the wall temperature on the transition location in the boundary-layer flow past a flat plate.

— In Section 9.2 shock/boundary-layer interaction is studied. For the laminar flow past a flat plate/ramp configuration numerical results show the influ­ence of different wall temperatures on the extent of the separation zone around the flat plate/ramp junction. The larger the wall temperature, the larger is the separation zone. The surface pressure distribution is affected accordingly.

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