Assessment of the Cold-Wire Resistance Thermometer for High-Speed Turbomachinery Applications

The paper first describes the fundamentals of cold-wire resistance thermometry. The transfer functions with and without wire-prong heat conduction effects are discussed and a new method for the description of complicated transfer functions describing both the prongs and wire frequency response is proposed. The experimental part of the paper starts with an investigation of the transfer function of various probes differing by the wire diameter, the l/d ratio, and the wire-prong connection using two simple methods: (1) electrical heating of the wire by a sine current and (2) a temperature step test consisting in injecting the probe into a hot air stream. The first test provides information on the wire response, whereas the second serves to study wire prong heat conduction effect. The tests cover a wide range of velocities and densities. A frequency bandwidth of 2 kHz is obtained with a 2.5 μm wire probe at an air velocity of 200 m/s at atmospheric pressure. A numerical compensation system allows us to extend the use of this probe to much higher frequencies. Finally, the probe is mounted onto a wheel in a high-speed rotating test rig allowing probe traverses through a stationary hot air jet at rotational speeds up to 5000 rpm with the probe positioned at a radius of 0.380 m. The probe signal is transmitted via an opto-electronic data transmission system. It is demonstrated that using the numerical compensation method, it is possible to reconstruct the hot jet temperature profile at frequencies up to 6 kHz.