INTRODUCTION This Item provides data for the estimation of the drag and pressure recovery of small auxiliary air inlets totally or partially immersed in the boundary layer. The prediction method given is applicable at subsonic speeds and is semi-empirical. In the main@ it uses a theoretical calculation of two-dimensional boundary-layer characteristics as a basis and modifies this in the light of the available experimental data. A qualitative introduction to the drag characteristics of scoop and flush inlets is given in Section 3. The drag quantities to be estimated are identified and the variation of overall drag with mass flow ratio is considered. The theoretical data that are of use in the prediction of inlet performance are contained in Derivation 13 which gives a two-dimensional analysis of the effect of boundary-layer thickness on the mass and momentum flows of a given streamtube along a flat plate. Derivation 13 also gives the pressure recovery just aft of the inlet plane for a thin-lipped inlet running full. Numerical values of the theoretical data have been extracted from Derivation 13 and are reproduced herein@ as described in Section 4. The drag of a scoop inlet protruding from the main surface and having a rectangular@ circular or semi-circular entry is considered in Section 5. The pressure recovery in the entry has been obtained from the theoretical calculations in Derivation 13 for full mass flow. A semi-empirical correction to allow for the loss in pressure recovery at lower mass flows has been added from Derivation 19. The drag of a flush inlet with a rectangular entry and an inlet ramp planform that is rectangular or of the NACA curved-divergent type is considered in Section 6. A prediction of the pressure recovery in the entry for a rectangular planform ramp has been obtained by making empirical corrections to the data from Derivation 13. A separate method is given for predicting the pressure recovery for inlets with a NACA curved-divergent ramp planform*. For both scoop and flush inlets the experimental data available are very restricted in their range of flow conditions and inlet geometries@ particularly in regard to lip profile@ which is often sharp for the configurations tested. This must be remembered when considering the empirical corrections made to the basic theoretical predictions. Section 7 on accuracy and applicability discusses this point in more detail. Section 8 lists the Derivation and References that have been used in producing this Item. Section 9 gives worked examples which compare the drag characteristics of scoop and flush inlets. * This method was previously issued in Item No. 66029. That Item has now been withdrawn since it is superseded by the present Item. A description of the basic method in Item No. 66029 in its original form is available in Reference 27.
ESDU 86002 B-1996 history
1996ESDU 86002 B-1996 DRAG AND PRESSURE RECOVERY CHARACTERISTICS OF AUXILIARY AIR INLETS AT SUBSONIC SPEEDS