GB791463A - Means inducing a flow of cooling air for internal combustion engines - Google Patents

Abstract

791,463. Gas turbine jet propulsion plant. KUZYK, W. Feb. 6, 1956 [Feb. 7, 1955], No. 3621/56. Class 110 (3). A gas turbine engine comprising an exhaust duct for the combustion products has a hood overlying the duct to form a cooling air passage in which a flow of cooling air is induced by a Coanda nozzle in the duct wall which is positioned to receive a portion of the combustion products and discharge them into the cooling air in the passage. A Coanda nozzle is a rectangular nozzle in which one of the edges of the nozzle is extended and removed continuously away from the initial direction of flow. A gas turbine engine comprising an air intake 11, compressor 12, combustion system 13, turbine 14 and exhaust system consisting of a tail bullet 15, tail cone 16, tail pipe 18 and outlet 19, is enclosed by a hood or nacelle 20 through which cooling air passes from apertures 23, and annular passage 24 to an annular nozzle 22. The passage 24 is of such a volume that the air in it has, for all practical purposes, zero velocity. A narrow, almost continuous peripheral slot 25 is cut in the aft portion of the tail pipe 18 and has at its upstream and downstream edges respectively a triangular shaped ring 26 and a peripheral ring 27 of aerofoil cross-section. The rings 26 and 27 may be formed of sheet metal welded to the tail pipe although shown as solid components. The rings 26, 27 and slot 25 form what is known as a Coanda nozzle 30. A small lip 31 attached to the downstream edge of the slot projects into the jet pipe and deflects a portion of the combustion products into the nozzle. The basis of the Coanda nozzle is shown in Fig. 2. If the nozzle flow at point B has a velocity V<SP>1</SP>, this velocity increases to V<SP>2</SP> at point C and to V<SP>3</SP> at point D and so on. This increase in velocity is accompanied by a decrease of pressure which is used to induce a flow of almost stagnant air from the chamber 24. Although the extended wall of the nozzle is shown in Fig. 2 by a finite number of straight lines the slope of which relative to the axis of the jet pipe decreases in a downstream direction, these lines may be replaced by a continuous curve as shown at 27. It is stated that this arrangement gives an increased thrust when compared with the usual arrangement in which the propulsion jet is used to suck cooling air through the cowling. Specification 456,063, [Group XXXIII], is referred to.