Application of particle image velocimetry to combusting flows: design considerations and uncertainty assessment

Methodological aspects concerning the application of the PIV technique to t he study of turbulent flames are discussed in this paper. The physical feat ures of the flow, which have implications for the experimental set-up, imag e processing and measurement accuracy are identified. Design considerations are developed focusing on several factors: spatial resolution, particle pe rformance, seeding technique, image formation and recording, and image post -processing for the evaluation of the displacement. Relevant uncertainty co ncerns are related to the effect of the thermophoretic force, acting on a s eeding particle while crossing the flame front, and to the non-homogeneity and time-dependence of the refractive index field. The uncertainty due to t hermophoresis is assessed by numerically studying the motion of a particle crossing a reference temperature profile. The effect of the refractive inde x variation is evaluated by means of theoretical analysis of light propagat ion and image formation, supported by experimental tests designed for this special purpose.