A remarkable change in nacelle plume geometry via iso-stagnation enthalpy is observed in Figure 16, when the freestream Mach number is increased from M∞ = 6.673 to 12.189. At M∞ = 12.189 and the altitude of 65.16 km, the nacelle plumes engulf the Skylon aft fuselage. The normalized temperatures at M∞ = 12.189 are significantly higher than those observed at M∞ = 3.508 [Figs. 16(b) and 13]. Figure 17 presents perspective views of the thermal environment around the aft fuselage and in a plane downstream of a Skylon nacelle. At M∞ ≥ 12.189, there are regions where the static temperature is roughly 8-16 times that of the freestream temperature. Where the SABRE plume shock wave hits the fuselage there is a static temperature spike. Subsequently, the static temperature again increases, as hot gases from engines pass over the aft fuselage [Figs. 17(c)-17 (d)]. As seen in Fig. 18, two plume shock waves, one from each SABRE, intersect at the vehicle symmetry plane. In front of the vertical tail, there is a bow shock wave. This shock wave also elevates static temperatures on the fuselage around the base of the vertical tail.
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