Drag due to a leak discharging into an external stream
ESDU 16006 provides a method of predicting the drag due to a leak which discharges into an external stream. A leakage flow discharging into an external stream affects drag in two main ways. First, the leakage efflux momentum exiting the leak orifice contributes directly to the drag. Second, the interference effects of the emerging leakage flow on the external flow boundary layer are expected, in some cases, to influence drag.
The drag due to leakage efflux momentum is the component of force due to the efflux momentum measured in the freestream direction. It may have a positive value (i.e. drag) or a negative value (i.e. a thrust) depending on the location of the leak on the air vehicle, the geometry, size and orientation of the leak orifice and the external flow conditions. The drag component due to the interference of the leakage flow with the external flow boundary layer is dependent on the geometry and orientation of the leak orifice, as well as the leak mass flow rate.
The method requires knowledge of the leak orifice area together with values of the maximum orifice dimensions in both the streamwise direction and perpendicular to it. Leak mass flow ratio is also required and is obtained using ESDU 16005.
The method is derived using test data for flows discharging into external streams through various well-defined orifice geometries in thin plates. The method is applicable to rectangular, square, elliptical and circular orifice geometries. In addition to these geometries the method should also be applicable to other similar geometries. A sketch comparing predicted leak drag coefficient data with test data shows that in most cases predictions lie within ± 0.1 for rectangular orifices and ± 0.05 for circular orifices.
|Data Item ESDU 16006|