An Empirical Inlet Pressure Recovery Model for Engine Inlet Barrier Filters for Rotorcraft Applications

From the Navier-Stokes momentum equation, this paper presents the application of Darcy's law for flows at moderate Reynolds numbers and thin filter media in the development of an empirical model of engine inlet total pressure recovery for rotorcraft (helicopters in particular) equipped with an Engine Inlet Barrier Filter (EIBF). The assumptions and limitations of the empirical model are discussed. The model treats the inlet filter media, structural features, and geometry as an integrated entity and has been validated using flight test data for three inlet configurations. The validation has been performed by directly comparing the model-predicted inlet recovery map with inlet total pressure measurements. The potential applications of the model are also discussed.