Adjunto una imagen:

Se puede observar, desde fuera hacia dentro, la salida de aire de derivación del ventilador ("Fan"), luego el escape de los gases del núcleo y, por último, está el cono que sobresale en la parte posterior, que tiene un orificio. Y es eso lo que no sé para que es. :)
EDITO:
He encontrado esto en inglés, a ver si lo puedo digerir correctamente:
"In some configurations, a small hole is located in the exit tip of the cone. This hole allows cooling air to be circulated from the aft end of the cone, where the pressure of the gases is relatively high, into the interior of the cone and consequently against the face of the turbine wheel. The flow of air is positive, since the air pressure at the turbine wheel is relatively low due to rotation of the wheel; thus air circulation is assured. The gases used for cooling the turbine wheel return to the main path of flow by passing through the clearance between the turbine disk and the inner cone. The exhaust cone assembly is the terminating component of the basic engine. The remaining component (the exhaust nozzle) is usually considered an airframe component.".