Leakage Through Loaded Flat-Flanged Joints without Gaskets

Abstract

Experimentally determined air leakage data are interpreted using fluid flow theory, finite element deflections and initial gap measurements. It is shown that laminar flow equations do not apply at practical aero-engine pressures and that the leakage flow can be overestimated by assuming choked isentropic flow at the outside diameter of the joint. Design against leakage is thereby reduced to a structural consideration of gap height at the outside diameter. It is shown that the gap height will usually reduce with load. A ‘divergent’ initial gap is shown to cause excessive leakage. However, the machining of a very small cone angle on the contact face is shown to be an effective method of significantly reducing leakage.