Abstract: A stall prediction apparatus of an axial compressor provided with: a rotor provided with a plurality of rotor blades; and a cylindrical casing facing the rotor blades and provided so as to cover the outer circumference of the rotor, comprising: pressure sensors provided in equal numbers at a plurality of locations in a circumferential direction of an inner wall surface of the casing, an index calculator for calculating an index (stall risk index) for evaluating the stall risk based on time-series data detected by each of the pressure sensors, and a signal processor for predicting the stall occurrence based on the stall risk indexes obtained corresponding to said each of the pressure sensors. In accordance with the present invention, it is possible to obtain a stall risk index which is highly accurate (supersensitive) and stable necessary for the active stall control, and to realize an engine control system with high reliability.

Abstract: A cavity has a longitudinal hollow having opposite open ends. An excitation source, such as a YAG rod, is accommodated in the hollow of the cavity. A hollow, cylindrical rod holder is inserted into each of the opposite open ends of the hollow and is fitted over a corresponding end of the YAG rod. A seal is fitted into a hollow of the rod holder adjacent to a portion of the rod holder fitted over the end of the YAG rod. The seal includes an annular seal body with a U-shaped section, e.g. made from Teflon®, and fitted over an outer periphery of the YAG rod to grip the YAG rod, as well as a spring fitted in a groove of the seal body provided by the U-shaped section so as to circumferentially surround a gripped portion of the YAG rod.