Device for mixing two flows of fluid, which are initially guided separate from one another, in a bypass jet engine
The invention relates to a device for mixing two fluid flows, which are initially guided separately from one another, in a bypass jet engine.
To this end, it is known that “lobe mixers” are used in bypass jet engines in order to mix the hot core stream of the jet engine and the cold bypass flow before discharge from the jet engine nozzle. In this case, the hot core stream of the jet engine is guided through a “mixing tube”, whereas the cold bypass flow flows along the outside of the mixing-tube lateral surface. The mixing of the two fluid flows is forced by the special shaping of the downstream lateral surface of the mixing tube. For this purpose, that lateral surface of the mixing tube which is formed downstream has “lobes” which extend radially outward. In this case, after flow has taken place through or respectively around the downstream section of the mixing tube, these lobes direct said hot core stream into the cold bypass flow, and also direct the cold bypass flow into the hot core stream. With regard to the known prior art, reference is made, for example, to GB 2 160 265 A.
A disadvantage with these known lobe mixers is in this case the fact that the lobe mixers, on account of the large radial extent of the lobes at the downstream end, tend to vibrate and in addition deformations occur due to material heating and pressure differences. It has therefore been attempted to remove these disadvantages by “struts” which support the lobe mixer on the outlet cone or the nozzle housing of the reaction engine. However, these struts constitute an additional source of weight.
In addition, on account of the large radial extent of the lobes of the lobe mixer, interference may occur in the region of the engine suspension between the lobes of the lobe mixer and the engine suspension. To avoid such interference, the relevant lobes of the lobe mixer, the “pylon lobes”, are designed differently. However, this has the disadvantage that a decrease in the mixing efficiency is associated with the redesign of the “pylon lobes”.
The object of the invention is to provide a remedy here by a new design of the device for mixing the hot core stream of the reaction engine with the cold bypass flow.
Based on a device of the type mentioned at the beginning, this object is achieved according to the invention in that the mixing tube is designed in the form of a truncated cone narrowing in the direction of flow of core stream and bypass flow, and in that the mixing tube has openings arranged at the downstream end in the circumferential direction of the mixing-tube lateral surface in a cross-sectional plane lying perpendicularly to the longitudinal axis of the mixing tube, through which openings the hot core stream flowing through the mixing tube penetrates into the cold bypass flow flowing around the mixing-tube lateral surface.
The mixing tube design according to the invention leads to substantial advantages. By the openings being provided in the mixing-tube lateral surface, lobe mixers with the large radial extent of their lobes are dispensed with. The vibration tendency is thus substantially reduced, so that the hitherto requisite struts are dispensed with. The risk of possible interference with the engine suspension thus does not arise either. In addition, the smaller radial extent has the advantage that the novel mixing tube according to the invention is also suitable for confined installations.
Furthermore, the closed annular lateral surface at the downstream end of the mixing tube leads to a robust, low-vibration construction, so that disturbances on account of fluctuations in operating pressure and temperature have less effect on the mixing tube. Since supporting struts are no longer necessary for fixing the mixing tube, this omission of the supporting struts at the same time also entails a lighter construction and thus lower weight of the reaction engine.
Furthermore, the simplified form of the mixing tube leads to a more cost-effective production, since the complicated deep-drawing operations required for producing the lobes are dispensed with.
According to a further feature of the invention, the openings in the mixing-tube lateral surface have passage areas of elliptical shape with a major axis and a minor axis. In this case, the major axis of the elliptical passage areas runs on the mixing-tube lateral surface in the direction of flow of the hot core stream and of the cold bypass flow, and the minor axis is arranged perpendicularly thereto.
Further features of the invention follow from the subclaims.
A combination of the novel mixing tube according to the invention with sufficiently well-known conventional lobe mixers is possible. The replacement of existing mixers with mixers according to the invention is conceivable, since the changes of the new mixer regarding mixer efficiency (lower) and overall pressure loss (lower) act in a neutral manner with regard to the gain in thrust.
The invention is described below with reference to an exemplary embodiment shown more or less schematically in the drawing.