The rotating rake fan mode measurement system

Abstract

An experimental measurement system was developed and implemented by the NASA Glenn Research Center in the 1990s. The system is a continuously rotating radial rake immersed into the duct. This rotating rake provides a complete map of the acoustic duct modes present in a ducted fan and has been used on a variety of test articles: from a low-speed, concept test rig to a full-scale production turbofan engine. The rotating rake has been critical in developing and evaluating a number of noise reduction concepts as well as providing experimental databases for verification of several aero-acoustic codes. This paper will describe the physical theory (Sofrin) and the analytical techniques (Moore) upon which the rotating rake is based will be described. Data processing and analysis as well as implementation issues will be discussed. Several Rotating Rake systems have been custom built for 3 facilities. In order of complexity of the turbo machinery test article, these are (1) the Advanced Noise Control Fan, (2) various 22-inch fan rigs in the NASA Glenn 9×15 wind tunnel, and (3) a full scale turbofan, the Honeywell TFE-731-60. Descriptions and measurement achievements of these systems will be provided (Heidelberg, Sutliff).