<p>With increasingly tighter tip
clearances in modern turbomachinery, it is essential to precisely measure this
parameter during turbomachinery characterization. Benefits from measuring tip
clearances include monitoring the structural integrity of the machine and estimating
aerodynamic losses incurred due to leakage flows. At present, capacitance probes
are one of the most commonly used sensors for tip clearance measurements in
turbomachines as they are accurate and robust. One of the main challenges when using
capacitance probes is properly calibrating the sensors, which usually involves
complex positioning systems and blade representative targets. This manuscript
describes in detail the development of a
methodology for in-house calibration of capacitance probes for tip clearance
measurements. A novel calibration procedure that does not involve rotating
components is investigated and compared against established calibration
methods. First, a calibration bench was developed to demonstrate the static and
dynamic performance of the acquisition system and perform quasi-static as well
as dynamic calibrations in a controlled environment. An in-situ methodology was
then developed to calibrate the sensors once installed in a two-stage rotating
turbine rig. The proposed methodology does not require complex positioning
systems and a regression analysis using a least squares scheme resulted in a coefficient
of determination of 0.9998. The calibration was validated using specially
designed instrumentation at various speeds that span the operating envelope of
the rig. A Bayesian model that was developed to estimate measurement
uncertainties for each method showed that uncertainties as low as ± 5μm can be
achieved with the proposed system. The proposed methodology was used in a two-stage
turbine rig. Measurements taken at three different circumferential locations
were subsequently used to map the spatial distribution of tip clearances throughout
the speed operational envelope of the turbine. Finally, a reduced order rotor displacement
model was developed and fitted to capacitance probes data. The work presented
in this thesis lays the foundation for high fidelity tip clearance measurement
capabilities at the Purdue Experimental Turbine Aerothermal Laboratory and can
be implemented into any rotating rig. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14750925 |
| Date | 08 June 2021 |
| Creators | Santiago D Salinas (10941474) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY-ND 4.0 |
| Relation | https://figshare.com/articles/thesis/SENSOR_CALIBRATION_SYSTEM_AND_METHODOLOGY_FOR_TIP_CLEARANCE_MEASUREMENTS_IN_TURBOMACHINES/14750925 |
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