System for infrared emission suppression (sires)

A film cooling apparatus adapted to be connected downstream of an exhaust conduit carrying hot exhaust gases from an aircraft gas turbine engine to prevent direct sighting of the exhaust conduit by infra-red detecting devices, said film cooling apparatus being formed about the longitudinal central axis extending from the exhaust conduit and comprising:

• means for supplying cooling fluid;
• a contoured body connected to an exhaust conduit symmetrically located about said longitudinal central axis having internal and external surfaces and a single thickness of material therebetween, said contoured body having an upstream end proximal to the exhaust conduit of increasing cross section relative to said longitudinal central axis, a center of maximum cross section and a downstream end distal to the exhaust conduit of decreasing cross section, said contoured body having first annular passages for the flow of cooling fluid therebetween, said passages comprising upstream edges which curve radially outwardly to promote generally laminar flow of cooling fluid through said first annular passages such that a first film flow is formed on said internal surface of said contoured body;
• a plurality of hollow struts extending radially inwardly from said upstream end of said contoured body;
• a tear-drop shaped hollow, inner body supported by said tubular struts radially inwardly and concentrically within said contoured body, said inner body having an interior, an exterior surface, an upstream end proximal to the exhaust conduit and a downstream end distal to the exhaust conduit and having a plurality of second annular passages therebetween, said hollow struts operating to deliver cooling fluid from said cooling means to the interior of said inner body and through said second annular passages so as to form a second film flow adjacent the interior surface of said inner body, said inner body having a turbulence generator located slightly upstream of the downstream end of said inner body comprising a ring and plate combination, said ring being positioned slightly upstream of said plate;
• said turbulence generator operating to promote mixing of cooling fluid from within said inner body with the exhaust gases;
• said contoured body and said inner body being so positioned that the exhaust gases escaping from the exhaust conduit pass through a passage defined by said internal surface of said contoured body and said exterior surface of said inner body, said inner body and said contoured body being aerodynamically configured and positioned to generate a zero pressure gradient in the flow of exhaust gases in said passage thereby promoting stability of said first and second film flows and facilitating efficient film cooling of the external surface of said inner body and the internal surface of said contoured body;
• a network of thermally insulated ducting located radially outwardly of said contoured body which carries cooling fluid from said cooling means to said contoured duct, said ducting and said contoured body operating to form a plenum chamber therebetween, said cooling fluid within said plenum chamber operating to cool of said external surface of said contoured body;
• an entraining diffuser connected to said contoured body at its downstream end extending along said longitudinal central axis and having a series of third annular passages, said diffuser operating to entrain quantities of cooling fluid into the exhaust gases;
• whereby the maintenance of a zero pressure gradient within said passage promotes the stability of said first and second film flows which form over the respective internal and external surfaces of said contoured body and said inner body to maintain the temperatures of the respective surfaces to a low radiation level by substantially precluding transmission of heat from the exhaust gases to said contour body and said inner body.

A film cooling apparatus adapted to be connected downstream of an exhaust conduit carrying hot exhaust gases from an aircraft gas turbine engine to prevent direct sighting of the exhaust conduit by infra-red detecting devices, said film cooling apparatus being formed about the longitudinal central axis extending from the exhaust conduit and comprising:

• means for supplying cooling fluid;
• a contoured body connected to an exhaust conduit symmetrically located about said longitudinal central axis having internal and external surfaces and a single thickness of material therebetween, said contoured body having an upstream end proximal to the exhaust conduit of increasing cross section relative to said longitudinal central axis, a center of maximum cross section and a downstream end distal to the exhaust conduit of decreasing cross section, said contoured body having first annular passages for the flow of cooling fluid therebetwen, said passages comprising upstream edges which curve radially outwardly to promote generally laminar flow of cooling fluid through said first annular passages such that a first film flow is formed on said internal surface of said contoured body;
• a plurality of hollow struts extending radially inwardly from said upstream end of said contoured body;
• a tear-drop shaped, hollow, inner body supported by said tubular struts radially inwardly and concentrically within said contoured body, said inner body having an interior an exterior surface, an upstream end proximal to the exhaust conduit and downstream end distal to the exhaust conduit and having a plurality of second annular passages therebetween, said hollow struts operating to deliver cooling fluid from said cooling means to the interior of said inner body and through said second annular passages so as to form a second film flow adjacent the interior surface of said inner body;
• said contoured body and said inner body being so positioned that the exhaust gases escaping from the exhaust conduit pass through a passage defined by said internal surface of said contoured body and said exterior surface of said inner body, said inner body and said contoured body being aerodynamically configured and positioned to generate a zero pressure gradient in the flow of exhaust gases in said passage to thereby promote stability of said first and second film flows and facilitating efficient film cooling of the external surface of said inner body and the internal surface of said contoured body;
• a network of thermally insulated ducting located radially outwardly of said contoured body which carries cooling fluid from said cooling means to said contoured duct, said ducting and said contoured body operating to form a plenum chamber therebetween, said cooling fluid within said plenum chamber operating to cool of said external surface of said contoured body;
• whereby the maintenance of a zero pressure gradient within said passage promotes the stability of said first and second film flows which form over the respective internal and external surfaces of said contoured body and said inner body to maintain the temperatures of the respective surfaces to a low radiation level by substantially precluding transmission of heat from the exhaust gases to said contoured body and said inner body.