Incorporation of an infrared suppressor is generally accompanied by a compromise in engine performance, which indirectly reduces the effectiveness of infrared signature suppression. This investigation illustrates the percentage increase in the infrared signature level in the 1.9-2.9 μm and 3-5 μm bands resulting from an increase in engine backpressure in a jet engine due to a reduction in the exit area of a choked converging nozzle. The effectiveness of optically blocking the hot engine parts by reducing the choked nozzle-exit area is estimated. Thermodynamic offdesign point analysis of the jet engine is done using GasTurb software to evaluate the percentage reduction in thrust and the net change in infrared signature level for the reduced choked converging nozzle-exit area relative to that for the design point. NomenclatureA ne = converging nozzle-exit area, m 2 A ne;dp = design point nozzle-exit area, m 2 A pl = planar projected area of discretized elements of engine components, m 2 c = velocity of light in vacuum; 2.99792 × 10 8 , m∕s D a = axial distance measured from the turbine-exit disk, m E = irradiance incident on a surface; ∫ E λ dλ, W∕m 2 F = thrust, kN F C = engine thrust with converging nozzle, kN F C−D = engine thrust with converging-diverging nozzle, kN h = Planck's constant; 6.62606 × 10 −34 , J · s k = Boltzmann's constant; 1.38065 × 10 −23 , J∕K L = directional radiance from a surface; ∫ L λ dλ, W∕m 2 · sr M e = nozzle-exit Mach number M ∞ = flight Mach number _ m = engine mass flow rate, kg∕s P = absolute pressure, kPa P o = nozzle total pressure, kPa T = absolute temperature of a surface, K T e = temperature at the nozzle exit, K V e = exhaust gas velocity at the nozzle exit, m∕s α = semicone angle, deg Δ = difference operator ΔA ne % = percentage change in A ne relative to A ne;dp ΔA ne;red % = percentage reduction in A ne relative to A ne;dp ΔF% = percentage change in thrust relative to F dp for case 1 ΔIRSL% = percentage change in infrared signature level relative to the design point infrared signature level λ = wavelength, μm λ 1 = lower limit of detector's wavelength band λ 2 = upper limit of detector's wavelength band τ = atmospheric transmissivity between infrared detector and aircraft along a line of sight ϕ = viewing aspect angle; 0 deg for direct rear view along engine axis, deg ω = solid angle subtended, srSubscripts atm = atmospheric bg-tp = background replaced by tailpipe in detector's field of view det = infrared detector dp = design point f = constant design point thrust IS = internal source jp = jet pipe red = due to a reduction in the choked converging nozzleexit area T = constant turbine-exit temperature tp = tailpipe λ = spectral quantity λ 1 − λ 2 = in detector's wavelength band λ 1 − λ 2 1 = decrease in infrared signature level for case 1 2 = increase in infrared signature level for case 2 I = i n1.9-2.9 μm band II = in 3-5 μm band

No abstract

No abstract

No abstract

No abstract