ESDU 80037:1980

ESDU 80037 provides a method for estimating the pressure recovery of axisymmetric intakes at subsonic speeds. The method is based on a semi-empirical correlation of a wide range of experimental data, including many unpublished results. The two main components of intake loss, associated with the lip and the diffuser portions of the intake, are considered separately. ESDU 80037 provides the data needed to estimate values for each of these components, the interaction between them, and to determine other minor components of pressure loss arising from straight portions of intake between the lip and diffuser and between the diffuser and the engine entry. The effects of nacelle incidence, which can be taken to include sideslip in crosswind conditions, are taken into account. The data apply to axisymmetric intakes, such as those on pylon-mounted engine pods, with sharp or rounded lips, and with entry contraction ratios up to 1.4. Diffusers having area ratio up to 7, with semi-angle up to 10 degrees, are covered. These ranges cover all currently practical requirements for axisymmetric intakes. The data are presented for aircraft flying at Mach numbers up to 0.8 for zero engine incidence, and (at take-off and landing speeds) for engine incidences up to 25 degrees. The calculation method applies for intake mass flows up to the choking condition. A method is included for estimating approximately, when required, the pressure losses under choked flow conditions. Two comprehensive worked examples on the use of the data are included.