DEVELOPMENT OF NEW CASCADES WITH PROFILES OF VARIABLE GEOMETRY FOR APPLICATION IN INLET AND EXIT GUIDE VANES OF SWIRL CONTROLLED TURBOMACHINES .1.

The control of axial flow turbomachines by variable geometry inlet and exit guide vanes is a very economical control method with regard to investment and maintenance costs. On the other side, the method in its present state of development is not as good (in terms of efficiency) as some of the other, more expensive methods - the method of variable geometry rotors for example. In order to develop the effectiveness of the variable stator method to the same level as that of the variable rotor method, new inlet and exit guide vanes have to be designed for axial flow machines like pumps. blowers and compressors. The present work, published in this and the next issue of the periodical (part I and II), describes theoretical and experimental investigations having been accomplished to develop new guide vane and stator cascades with optimized profiles having extremely extended low loss regions compared to those of the usual cascades with conventional profiles. On the theoretical side two direct design methods are introduced, methods by which inlet and exit cascades with special profiles can be generated and optimized with regard to a maximum working range with minimum losses. In case of the inlet guide vanes these are unstaggered cascades of profiles with mechanical flaps at the rear ends and in case of the exit guide vanes these are tandem cascades having variable stagger blades in the first blade row. On the experimental side the measured results for two newly designed inlet and exit cascades are presented and compared to the pertinent results of conventionally designed cascades. Thereby the most important results of these investigations become evident, namely: With the newly developed cascades it is demonstrated that the low loss inlet angle range can be increased by 260% in case of the inlet cascade, by 150% in case of a single row exit cascade and by 250% in case of the double row or tandem exit cascade with variable stagger blades in the first row. This article is published in two parts. Part I deals with inlet cascades, part II deals with stator cascades.