Dual flow turboshaft engine and improved hot flow nozzle

1. A bypass turbojet engine for an aircraft, provided with a longitudinal axis, said bypass turbojet engine comprising:

a nacelle delimiting, at a front portion of the turbojet engine, an air intake and axially containing a cold flow fan for generating a cold flow and a hot flow generator for generating a hot flow, with a turbine casing ending at a rear portion of the turbojet engine, and with a bulbous boss being connected to said turbine casing along a first connecting surface;

an engine cowl containing said hot flow generator, wherein said engine cowl comprises:

an external wall delimiting with said nacelle a cold flow duct, in which the cold flow duct is configured for flowing the cold flow generated by the cold flow fan and ends at a rear portion of the engine cowl, forming a cold flow nozzle, and

an internal wall delimiting with said turbine casing a hot flow duct configured for flowing the hot flow generated by the hot flow generator;

a hot flow nozzle extending from said internal engine cowl wall in a rearward direction, with the hot flow nozzle being connected to the internal engine cowl wall along a second connecting surface and positioned relative to said bulbous boss to delimit a nominal nozzle throat section and a nominal outlet section for the hot flow to flow from said hot flow generator, and

at least one ventilation opening positioned between said external wall of said engine cowl and said hot flow nozzle, with said at least one ventilation opening being outside said cold flow nozzle, and configured to discharge to the outside of the turbojet engine a ventilation air flow, bled from said cold flow generated from said cold flow fan and into said engine cowl, to temperature regulate said hot flow generator,

wherein:

said hot flow nozzle extending from said internal engine cowl wall is formed as a single skin having an external wall over which the ventilation air bled from the cold flow flows and an internal wall over which the hot flow flows, wherein said single skin is bulbous in shape, widening in diameter continuously along the longitudinal axis from said second connecting surface in a direction toward said external wall of said engine cowl, and said single skin is configured to include a concave shaped portion facing toward the bulbous boss in which there is no separation of the hot flow through the hot flow duct;

said ventilation opening is at a largest-diameter part along the single skin; and

said bulbous boss connected to said turbine casing is configured relative to said single skin to form said nominal nozzle throat section and said nominal outlet section of said hot flow nozzle.

2. The turbojet engine as claimed in claim 1 , wherein said hot flow nozzle throat coincides with said hot flow outlet.

3. A hot flow nozzle for a bypass turbojet engine for an aircraft, wherein said bypass turbojet engine is provided along a longitudinal axis and comprises:

a nacelle delimiting, at a front portion of the turbojet engine, an air intake and axially containing a cold flow fan for generating a cold flow and a hot flow generator for generating a hot flow, with a turbine casing ending at a rear portion of the turbojet engine, and with a bulbous boss being connected to said turbine casing along a first connecting surface;

an engine cowl containing said hot flow generator, wherein said engine cowl comprises:

an external wall delimiting with said nacelle a cold flow duct, in which the cold flow duct is configured for flowing the cold flow generated by the cold flow fan and ends at a rear portion of the engine cowl, forming a cold flow nozzle, and

an internal wall delimiting with said turbine casing a hot flow duct configured for flowing the hot flow generated by the hot flow generator;

a hot flow nozzle extending from said internal engine cowl wall in a rearward direction, with the hot flow nozzle being connected to the internal engine cowl wall along a second connecting surface and positioned relative to said bulbous boss to delimit a nominal nozzle throat section and a nominal outlet section for the hot flow to flow from said hot flow generator, and

at least one ventilation opening positioned between said external wall of said engine cowl and said hot flow nozzle, with said at least one ventilation opening being outside said cold flow nozzle, and configured to discharge to the outside of the turbojet engine a ventilation air flow, bled from said cold flow from said cold flow generated from said cold flow fan and into said engine cowl, to temperature regulate said hot flow generator,

wherein:

said hot flow nozzle extending from said internal engine cowl wall is formed as a single skin having an external wall over which the ventilation air bled from the cold flow flows and an internal wall over which the hot flow flows, wherein said single skin is bulbous in shape, widening in diameter continuously along the longitudinal axis from said second connecting surface in a direction toward said external wall of said engine cowl, and said single skin is configured to include a concave shaped portion facing toward the bulbous boss in which there is no separation of the hot flow through the hot flow duct;

said ventilation opening is at a largest-diameter part along the single skin; and

said bulbous boss connected to said turbine casing is configured relative to said single skin to form said nominal nozzle throat section and said nominal outlet section of said hot flow nozzle.