Benchmarking a single-stem PIV endoscope in a spray

• Main Author: Lad, Neetin
• Other Authors: Aroussi, Abdelwahab ; Rona, Aldo ; Gao, Shian
• Published: University of Leicester 2011
• Subjects: 620.106
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548399

Flows with a limited optical access for PIV measurement can be probed using endoscopic PIV techniques. Conventional endoscopic PIV utilises two separate probes, one to relay a light sheet and the other to provide imaging optics to capture a two-dimensional image of the flow. This research aims to validate the velocity measurements taken from the novel single-stem endoscopic PIV system. The specific objectives are to determine the accuracy of the single-stem endoscopic PIV result, identify any shortcomings in the technique, and identify improvements for future single-stem endoscopic PIV systems. The single-stem endoscopic PIV system is applied to an atomised spray flow and velocity measurements are compared with conventional PIV and Pitot-static data. The endoscopic PIV system provides localised velocity maps that are comparable with the measurements from the conventional PIV system. This comparison is based on the spray ensemble mean flow field and its fluctuating velocity component statistics. A detailed analysis on the hardware setup, image capture, calibration and pre/post processing techniques is carried out to identify possible sources of systematic error in the measurement and how the measurement uncertainty accumulates. The mean velocity vector map, recorded from the single-stem endoscopic PIV system was used to estimate the spray mass flow rate and its entrainment characteristics, the centreline velocity decay, and the spreading rate similar to the corresponding estimates from conventional PIV. Furthermore estimates of the localised Strouhal number and of the spray fluctuation are also compared. By considering the measurement uncertainty as an accumulation of a series of component uncertainties, this study has identified and quantified the uncertainty contribution from each component. The largest sources of uncertainty are primarily due to two components. The first is the optical aberration, which leads to image defocusing and reduction in particle identification. The second component is the larger uncertainty source which is the uneven illumination of the measurement plane.