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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

# High Temperature Fast Response Aerodynamic Probe

[+] Author and Article Information
Christian Lenherr

Department of Mechanical and Process Engineering, Laboratory for Energy Conversion, ETH Zurich, Sonneggstr.3, 8092 Zurich, Switzerlandlenherr@lec.mavt.ethz.ch

Anestis I. Kalfas

Aristotle University of Thessaloniki, School of Engineering, 54124 Thessaloniki, Greece

Reza S. Abhari

Department of Mechanical and Process Engineering, Laboratory for Energy Conversion, ETH Zurich, Switzerland

J. Eng. Gas Turbines Power 133(1), 011603 (Sep 17, 2010) (10 pages) doi:10.1115/1.4001824 History: Received April 08, 2010; Revised April 13, 2010; Published September 17, 2010; Online September 17, 2010

## Abstract

In order to advance the technology for measurements in higher temperature flows, a novel miniature (diameter 2.5 mm) fast response probe that can be applied in flows with temperatures of up to 533 K $(500°F)$ has been developed. The primary elements of the probe are two piezoresistive pressure transducers that are used to measure the unsteady pressure and unsteady velocity field, as well as the steady temperature. Additional temperature and strain gauge sensors are embedded in the shaft to allow a much higher degree of robustness in the use of this probe. The additional temperature sensor in the shaft is used to monitor and correct the heat flux through the probe shaft, facilitating thermal management of the probe. The strain gauge sensor is used to monitor and control probe shaft vibration. Entirely new packaging technology had to be developed to make possible the use of this probe at such high temperatures. Extensive calibration and thermal cycling of the probe used to bind the accuracy and the robustness of the probe. This novel probe is applied in the one-and-1/2-stage, unshrouded axial turbine at ETH Zurich; this turbine configuration is representative of a high work aero-engine. The flow conditioning stretch upstream of the first stator is equipped with a recently designed hot streak generator. Several parameters of the hot streak, including temperature, radial and circumferential position, and shape and size can be independently controlled. The interactions between the hot streak and the secondary flow present a perfect scenario to verify the probe’s capability to measure under real engine conditions. Therefore, measurements with the novel probe have been made in order to prove the principle and to detail the interaction effects with blade row pressure gradients and secondary flows.

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## Figures

Figure 1

FRAP-HT probe presented with a match for scale comparison

Figure 2

Yaw and pitch angle definition, including explanation of FRAP virtual four-sensor mode (stemwise rotation of the probe ±42 deg from the central position, p1)

Figure 3

Typical output signals, U (left) and Ue (right) in voltage (V), as a function of temperature and pressure, resulting from the probe sensor calibration

Figure 4

Aerodynamic calibration coefficient curves for flow angles, Kφ and Kγ, and for total and static pressure, Kt and Ks; calibration range: yaw is ±24 deg and pitch is ±20 deg

Figure 5

Piezoresistive miniature silicon chip including electrical schematic of Wheatstone bridge working principle

Figure 6

Amplitude response of both sensors of the FRAP-HT probe: the measured response results from grid-generated turbulence

Figure 7

Two views onto the same 6 mm FRAP-HT probe shaft presented with a match for scale comparison. The bottom view (PT100) shows the same shaft position as the top view (strain gauge) after a 180 deg stemwise rotation.

Figure 8

Cylindrical four-hole probe (FRAP shape) presented with a match for scale comparison

Figure 9

Close-up view of the one-and-a-half stage unshrouded axial research turbine equipped with a hot streak generator (inlet duct and vane-shaped support strut)

Figure 10

Normalized total temperature Ttot,mav/TMF measured with FRAP-HT at the inlet of stator 1 (pitchwise mass-averaged) for configurations 2 and 3

Figure 11

Steady normalized total temperature (Ttot/TMF) over one stator pitch. Ideal case simulation at the HS injection plane for configurations 2 (a) and 3 (c); FRAP-HT results at the inlet of stator 1 for configurations 2 (b) and 3 (d).

Figure 12

FRAP-HT pitchwise distribution of time-averaged Ttot/TMF (a) and flow yaw angle φ (b) at the span positions of the respective HS core for configurations 2 and 3

Figure 13

Pitchwise mass-averaged differences of FRAP, FRAP-HT, and 4HP (including error bars). (a) Deviation in flow angles φ and γ and (b) nondimensional pressures. All measured for configuration 1 at the exit of stator 1.

Figure 14

Time resolved (t/T=0.41) area plot at the exit of stator 1 measured for configuration 1 (absolute frame of reference); (a) Cpt measured with FRAP-HT. (b) Difference in Cpt FRAP and FRAP-HT, expressed by the rms at the same sample time.

Figure 15

Steady normalized total temperature (Ttot/TMF) over one stator pitch measured with FRAP-HT at the exit of the rotor for configurations 2 (a) and 3 (b).

Figure 16

Time resolved (t/T=0.85) area plot at the exit of the rotor measured with FRAP-HT and presented over one stator pitch (absolute frame of reference). (a) rms of the random part of Ptot for configuration 2 and (b) rms of the random part of Ptot for configuration 3.

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