Abstract:

This Data Item is the third in the series of Items concerned with the prediction of the drag of rectangular planform cavities for Mach numbers up to 3. ESDU 00006 (Part I) deals with cavities having closed flow, and ESDU 00007 (Part II) is for cavities having open or transitional flow. Those Items are only applicable to cavities without doors, so the present Data Item (Part III) completes the series with the provision of methods for the prediction of the drag of a pair of equal width doors open at 90°, typical of weapons bay applications.

The prediction methods use data (where available) from the ESDU Aerodynamics Series, and involve planar doors at subsonic or supersonic speeds. The effects of three types of door leading and trailing edges are considered: straight (i.e. unswept) with either square edges, chamfered (i.e. wedge or chiselled) edges or sawtoothed with chamfered edges. A summary of the door drag prediction components is given, including tables of the components and references to the relevant prediction equations. The way in which door drag is used in the determination of the total drag coefficient due to the presence of a rectangular cavity with doors open at 90° is also given.

The drag prediction methods for cavity doors were developed using wind-tunnel data for flat plates at zero angle of attack in uniform flows. As with the methods for the drag of cavities without doors (ESDU 00006 and ESDU 00007), in order to apply the methods to a practical situation in which a cavity with a pair of doors open at 90° is in a non-uniform flow, an artifice employed in the application of excrescence drag data is used, see ESDU 90029. With regard to base drag, ESDU 10017 provides a guide to the effectiveness of the various types of trailing-edge device used to alleviate the drag of blunt trailing edges. The possible use and appropriateness of such devices for weapons bay doors is discussed. In order to gain some appreciation of the effects on drag of the different door leading-edge and trailing-edge geometries, a set of examples based on the cavity in Example 2 of ESDU 00006 at M₁ = 0.8 and 2.0 is given.

The door drag prediction methods use available data from the ESDU Aerodynamics Series, but there are three main areas where there are no suitable ESDU data, and they are dealt with in Appendices A to C. Those areas concern the pressure drag due to blunt leading edges (Appendix A), blunt trailing edges (Appendix B) and chamfered (wedge) leading edges (Appendix C) of flat plates at subsonic speeds.

Software for the method is provided as ESDUpac A1607 and also with an interface as Toolbox 16007.