James M Kilpatrick

Measurement of complex surface deformation by high-speed dynamic phase-stepped digital speckle pattern interferometry

We describe a high-speed digital speckle pattern interferometer incorporating a line-scan camera and a waveguide phase modulator for the measurement of complex deformation (vibration phase and amplitude) at audio acoustic frequencies. Experimental data show continuous phase-stepped recovery of out-of-plane surface deformation in one dimension, obtained at 100 kHz with 2pi/20-rad (0.02-mum) displacement resolution, for surface velocities of 3.2 mm s>(-1) .

Miniature fiber optic pressure sensor for turbomachinery applications

Development of pressure sensors for the instrumentation of experimental aerodynamic facilities has traditionally concentrated on electrical techniques. An improvement in the currently attainable temporal and spatial resolution in pressure measurement would be beneficial in the characterization of turbulent flows behind turbine rotor stages, for example. We present results obtained in a turbine test rig from a fiber optic pressure sensor based upon the interferometric response of an extrinsic cavity formed between the interrogation fiber and a reflective diaphragm. We discuss the design trade offs, optical interrogation and temperature sensitivity of such a configuration, and demonstrate the success of the design in small-scale shock tube experiments. We then describe the application of the sensor in a full scale turbine test facility in which pressure signals with frequency components exceeding 200 kHz were obtained.

Measurement of unsteady gas temperature with optical fibre Fabry-Perot microsensors

We describe the application of thin-film optical fibre Fabry-Perot (FFP) microsensors to high-bandwidth measurement of unsteady total temperature in transonic gas flows. An aerodynamic probe containing two temperature sensitive FFP microsensors was deployed in the rotor exit flow region of a gas turbine research rig. Measurements reveal gas temperature oscillations typically 4 K peak to peak at the blade passing frequency of 10 kHz with components to the third harmonic detected in the power spectrum of the temperature signal.

Phase-demodulation error of a fiber-optic Fabry–Perot sensor with complex reflection coefficients

The influence of reflector losses attracts little discussion in standard treatments of the Fabry-Perot interferometer yet may be an important factor contributing to errors in phase-stepped demodulation of fiber optic Fabry-Perot (FFP) sensors. We describe a general transfer function for FFP sensors with complex reflection coefficients and estimate systematic phase errors that arise when the asymmetry of the reflected fringe system is neglected, as is common in the literature. The measured asymmetric response of higher-finesse metal-dielectric FFP constructions corroborates a model that predicts systematic phase errors of 0.06 rad in three-step demodulation of a low-finesse FFP sensor (R = 0.05) with internal reflector losses of 25%.

Heat-flux measurement using fibre-Bragg-grating Fabry-Pérot sensors

We describe a fibre Fabry-Perot heat-transfer sensor that is capable of performing the high-spatial-resolution measurements required in turbomachinery research. The all-fibre cavity operates as a calorimeter embedded perpendicular to the test surface. The cavity incorporates a Bragg grating as the internal reflector, producing a mechanically robust sensor suitable for aerodynamic measurements. We present experimental results from an impinging flow rig, comparing the optical sensor with a thin-film resistance gauge subjected to a step increase in heat flux of 30 kW m-2.

Miniature fiber optic pressure sensors for turbomachinery applications

Development of pressure sensor for the instrumentation of experimental aerodynamic facilities has traditionally concentrated on electrical techniques. Such transducers have temporal and spatial resolutions that are currently insufficient to provide the accurate measurement of turbulent flows behind turbine rotor stages, for example. We present result obtained in a turbine test rig form a simple fiber optic pressure sensor based upon the interferometric response of an extrinsic cavity formed between the interrogation fiber and a reflective diaphragm. We discuss the design trade-offs, optical interrogation and temperature sensitivity of such a configuration, and demonstrate the success of the design in small-scale shock tube experiments. We then describe the application of the sensor in a full scale turbine test facility.

Miniature fibre optic pressure sensor for high-resolution measurements in turbomachinery applications

There is considerable demand in the field of turbomachinery research to make in-situ measurements of temperature, heat flux, and pressure in large-scale flow rigs. This is driven by the desire to increase engine efficiency and reliability by improving our understanding of the flow regimes within compressors and turbines.

Optical Fibre Aerodynamic Probes for Total Pressure and Total Temperature Measurement in Turbomachinery

Optical fibre sensors offer the prospect of miniature aerodynamic probes for highly localised flow measurements in aerospace wind tunnels and turbomachines. We discuss the design and construction of optical fibre sensors for temperature and pressure. The temperature sensors consist of multilayer coatings deposited on the fibre end face from which the reflected intensity is temperature-dependent. Two sensors were incorporated in a dual heated probe to measure total temperature. The pressure sensors are miniature diaphragms in which pressure-induced deflection is measured interferometrically in reflection. We present results from initial trials made in unsteady flow in a single stage research turbine, in which total temperature data with harmonic components up to 30 kHz and total pressure signals up to 230 kHz were recorded.Copyright

Optical fibre probes for total pressure and total temperature measerement in a turbine test rig

We describe two probes which incorporate interferometric optical fibre sensors for gas total temperature and pressure measurements in transient flow rigs for turbomachinery research. Experimental results are presented from both probes deployed downstream of a turbine rotor.

Fibre optic microsensor for measurement of temperature dynamics in gas turbine systems

The use of computational fluid dynamics (CFD) to model the temperature and pressure distributions which drive complex thermodynamic processes in gas turbine systems contributes to more cost efficient turbine design and development. However, experimental measurements are still required for validation of full-field CFD models, particularly in regions of highly unsteady flow where model stability is most severely tested. THis work concerns the development of fiber optic temperature and pressure microsensors for measurements combining high spatial resolution and high bandwidth in unsteady gas flows. The objective of the work presented in this paper was to measure gas total temperature in a large- scale turbomachinery test-rig at DERA Pyestock, known as the Isentropic Light Piston Facility. We have accordingly designed a dual sensor system, in which one of the elements is heated, so that gas total temperature can be measured independently of the convective heat transfer coefficient. While such dual element probes based on thin-film resistance gauges have been developed previously for aerodynamic studies, this is the first report of their development using optical sensors.