On the Development and Application of the FRAP® (Fast-Response Aerodynamic Probe) System for Turbomachines: Part 1 — The Measurement System

Abstract

This contribution gives an overview of the current state, performance and limitations of the fast-response aerodynamic probe measurement system (FRAP® System) developed at the Turbomachinery Lab of the ETH Zurich. In particular, the following topics are addressed: • Probe technology: Miniature probes with tip diameter ranging from 0.84 to 1.80 mm (1-sensor and 3-sensor probes respectively) have been developed. New technologies derived from microelectronics and micromechanics have been used to achieve an adequate packaging of the microsensor chips used. Both the sensor packaging and the sensor calibration (time-independent and time-dependent) are crucial issues for the DC accuracy of any measurement. • Aerodynamic probe calibration: The methods used for the sensor calibration and the aerodynamic probe calibration, the pertinent automated test facilities and the processing of the output data are briefly presented. Since these miniature probes are also capable of measuring the mean flow temperature, aspects related to the recovery factor and the self-heating of the probe tip are treated and some recommendations related to sensor selection are given. • Measurement system and data evaluation: The early measurement chain described in Gossweiler, Kupferschmied and Gyarmathy 1995 has evolved into the FRAP® System. This automatic system incorporates dedicated measurement concepts for a higher accuracy and a more efficient operation in terms of time and failures. An overview of the data evaluation process is given. The FRAP® System has been tested in real-sized turbomachines under industrial conditions within the temperature limits of 140°C imposed by the sensor technology (axial-flow turbofan compressor, axial-flow turbine, centrifugal compressor). These applications confirmed the potential of the system and encouraged its further development. Now, the system is routinely used in the facilities of the Turbomachinery Lab and in occasional measurement campaigns in other laboratories. Part 2 of this contribution (Roduner et al.) will focus on the application of the FRAP® System in a transonic centri fugal compressor of the ETH Turbomachinery Laboratory, while Part 3 (Köppel et al.) treats more sophisticated data analysis methods.