Analysis of Infrared Signature from Aircraft Frontal Aspect due to Skin Friction Heating

At supersonic aircraft speeds, aerodynamically heated surfaces, e.g., nose, wing leading edges, are infrared (IR) signature sources from the tactically crucial frontal aspect. This study numerically predicts and then illustrates the minimization of IR contrast between the nose and background sky radiance by the emissivity optimization (ε_w,opt) technique, which has the least performance penalties. The IR contrast between the aircraft nose and its replaced background in 1.9-2.9 μm short-wave IR (SW-IR), 3-5 μm medium-wave IR (MW-IR), and 8-12 μm long-wave IR (LW-IR) bands are obtained. The IR contrast especially in LW-IR (i) increases with flight Mach number (M _∞) for a given flight altitude (H) and ε_w (ii) decreases with increasing H for a given M _∞ and ε_w. The ε_w,opt for a flight altitude of 5 km is found to decrease from 0.99 at M _∞ = 0.001 (low subsonic) in all three bands to 2 × 10⁻⁴ in MW-IR and 0.0213 in LW-IR bands at M _∞ = 3 (high supersonic). Maximum contrast radiance due to skin friction heating for a given ε_w is obtained in the LW-IR band up to M _∞ ≤ 2.5, which shifts to the MW-IR band for M _∞ > 2.5.