title: Performances of motion tracking enhanced Tomo-PIV on turbulent shear flows.
abstract: The motion tracking enhancement technique (MTE) is a recently introduced method to improve the accuracy of tomographic PIV measurements at seeding density higher than currently practiced. The working principle is based on the fact that the particle field and its projections are correlated between the two exposures. Therefore, information from subsequent exposures can be shared within the tomographic reconstruction process of a single object, which largely reduces the energy lost intoghost particles. The study follows a previous work based on synthetic particle images, showing that the MTE technique has an effect similar to that of increasing the number of cameras. In the present analysis, MTE is applied to Tomographic PIV data from two time-resolved experiments on turbulent shear flows: a round jet atRe= 5,000 (facq= 1,000 Hz) and a turbulent boundary layer at the trailing edge of an airfoil (Rec= 370,000) measured at 12,000 Hz. The application of MTE is extended to the case of more than two recordings. The performance is assessed comparing the results from a lowered number of cameras with respect to the full tomographic imaging system. The analysis of the jet flow agrees with the findings of numerical simulations provided the results arescaledtaking into account the concept of MTE efficiency based on the volume fraction whereghost-pairs(Elsinga et al. 2010a) are produced. When a large fraction of fluid has uniform motion (stagnant fluid surrounding the jet), only a moderate reduction inghost intensityis expected by MTE. Nevertheless, a visible recovery of reconstruction quality is observed for the 3-cameras system when MTE is applied making use of 3 recordings. In the turbulent boundary layer, the objective is set to increase the seeding density beyond current practice, and the experiments are performed at approximately 200,000 particles/megapixel. The measurement robustness is monitored with the signal-to-noise ratio S/N for the cross-correlation analysis. An estimate of the precision error is obtained for the turbulent boundary layer case following the peak height of the spatio-temporal cross-correlation function (frozen-turbulence). The MTE approach appears to be essential for the increase in robustness and measurement precision at such seeding density.
authors.affiliation: Department of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands.
authors.forename: Matteo
authors.initials: M
authors.lastname: Novara
authors.affiliation: Department of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands.
authors.forename: Fulvio
authors.initials: F
authors.lastname: Scarano