The main objective of this research is to propose a method for decomposing the total drag of a nacelle into external, internal, and wake drag. From a bookkeeping agreement, the internal drag (i.e., the drag generated inside a nacelle) is the engine manufacturer's responsibility and is not to be included in the aircraft's total drag. Consequently, computing the internal drag is mandatory for the airframe and engine constructors concerned and can be achieved either experimentally or by computational-fluid-dynamics analysis. Up to now, aerodynamic engineers have used a near-field approach to compute the internal drag using computational-fluid-dynamics analysis, but this method has serious drawbacks, including its dependency on the accurate location of the stagnation line. The new method proposed here has been applied to multiple two-and three-dimensional test cases, and results show that it is independent of the location of the stagnation line and yields accurate results that agree well with experimental and empirical data. Results also show that the wake drag of a through-flow nacelle is caused by the flow passing through the nacelle and so needs to be added to the internal drag.
Nomenclatureextrapolated near-field drag coefficient from a refinement study c = reference chord, m D NF = near-field drag (pressure friction), N D FF = far-field drag (viscous wave spurious induced), N D V = viscous drag, N D W = wave drag, N D I = induced drag, N D SP = spurious drag, N D c = configuration drag, N D Install = installation drag, N D WBPN = drag of a wing-body-pylon-nacelle configuration, N D WB = drag of a wing-body configuration, N D irr = irreversible drag (viscous wave spurious), N F V = viscous sensor F W = shock sensor f = momentum vector f vw = momentum vector associated with irreversible processes f i = momentum vector associated with reversible processes I = impulsion M = Mach number n = n x ; n y ; n z , normal vector pointing to the outside of the volume p = static pressure, kPa p ∞ = freestream static pressure, kPa q = u v w, velocity vector, m∕s R = perfect gas constant, J∕kg · K Re c = Reynolds number based on a reference chord S ref = reference area, m 2 S A = aircraft surface area S ∞ = surface surrounding the configuration where the flow is undisturbed S T = Trefftz's plane u, v, w = velocity components in the x, y, and z directions, m∕s u ∞ = freestream velocity, m∕s= spurious volume α = angle of attack, deg γ = ratio of specific heats ΔH = enthalpy variation from the freestream state, J∕kg Δs = entropy variation from the freestream state, J∕K Δ u = axial velocity defect, m∕s μ l = laminar viscosity, N · s∕m 2 μ t = turbulent viscosity, N · s∕m 2 μ ∞ = freestream viscosity, N · s∕m 2 ρ = density, kg∕m 3 ρ ∞ = freestream density, kg∕m 3 τ x = τ xx τ xy τ xz , vector of viscous deviatoric stresses, N∕m 2
