title: Large-aperture, tapered fiber-coupled, 10-kHz particle-image velocimetry.
abstract: We demonstrate the design and implementation of a fiber-optic beam-delivery system using a large-aperture, tapered step-index fiber for high-speed particle-image velocimetry (PIV) in turbulent combustion flows. The tapered fiber in conjunction with a diffractive-optical-element (DOE) fiber-optic coupler significantly increases the damage threshold of the fiber, enabling fiber-optic beam delivery of sufficient nanosecond, 532-nm, laser pulse energy for high-speed PIV measurements. The fiber successfully transmits 1-kHz and 10-kHz laser pulses with energies of 5.3 mJ and 2 mJ, respectively, for more than 25 min without any indication of damage. It is experimentally demonstrated that the tapered fiber possesses the high coupling efficiency (~80%) and moderate beam quality for PIV. Additionally, the nearly uniform output-beam profile exiting the fiber is ideal for PIV applications. Comparative PIV measurements are made using a conventionally (bulk-optic) delivered light sheet, and a similar order of measurement accuracy is obtained with and without fiber coupling. Effective use of fiber-coupled, 10-kHz PIV is demonstrated for instantaneous 2D velocity-field measurements in turbulent reacting flows. Proof-of-concept measurements show significant promise for the performance of fiber-coupled, high-speed PIV using a tapered optical fiber in harsh laser-diagnostic environments such as those encountered in gas-turbine test beds and the cylinder of a combustion engine.
authors.affiliation: Spectral Energies, LLC, 5100 Springfield Street, Suite 301, Dayton, Ohio 45431, USA.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Hsu
authors.forename: Sukesh
authors.initials: S
authors.lastname: Roy
authors.forename: Naibo
authors.initials: N
authors.lastname: Jiang
authors.forename: James R
authors.initials: JR
authors.lastname: Gord
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation* / Q000379:methods*; D012031:Refractometry / Q000295:instrumentation*; D012212:Rheology / Q000295:instrumentation* / Q000379:methods