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A test case for pressure field reconstruction from particle image velocimetry (PIV) and Lagrangian particle tracking (LPT) has been developed by constructing a simulated experiment from a zonal detached eddy simulation for an axisymmetric base flow at Mach 0.7. The test case comprises sequences of four subsequent particle images (representing multi-pulse data) as well as continuous time-resolved data which can realistically only be obtained for low-speed flows. Particle images were processed using tomographic PIV processing as well as the LPT algorithm ‘Shake-The-Box’ (STB). Multiple pressure field reconstruction techniques have subsequently been applied to the PIV results (Eulerian approach, iterative least-square pseudo-tracking, Taylor’s hypothesis approach, and instantaneous Vortex-in-Cell) and LPT results (FlowFit, Vortex-in-Cell-plus, Voronoi-based pressure evaluation, and iterative least-square pseudo-tracking). All methods were able to reconstruct the main features of the instantaneous pressure fields, including methods that reconstruct pressure from a single PIV velocity snapshot. Highly accurate reconstructed pressure fields could be obtained using LPT approaches in combination with more advanced techniques. In general, the use of longer series of time-resolved input data, when available, allows more accurate pressure field reconstruction. Noise in the input data typically reduces the accuracy of the reconstructed pressure fields, but none of the techniques proved to be critically sensitive to the amount of noise added in the present test case., Aerodynamics

A test case for PIV-based pressure evaluation techniques has been developed by constructing a simulated experiment from a ZDES simulation for an axisymmetric base flow at Mach 0.7. The test case comprises sequences of four subsequent particle images (representing multi-pulse data) as well as continuous time-resolved data. Particle images were processed using tomographic PIV processing as well as the PTV algorithm ‘Shake-The-Box’. Multiple pressure reconstruction techniques have subsequently been applied to the PIV results (Eulerian approach, iterative least-square pseudo-tracking, Taylor’s hypothesis approach, instantaneous Vortex-in-Cell) and PTV results (FlowFit, Vortex-in-Cell-plus, Voronoi-based pressure evaluation and iterative least-square pseudo-tracking). All methods were able to reconstruct the main features of the instantaneous pressure fields, including methods that reconstruct pressure from a single PIV velocity snapshot. Highly accurate pressure field reconstructions could be obtained by using PTV approaches in combination with more advanced techniques. In general, the use of longer series of time-resolved input data, when available, allows more accurate pressure field reconstruction. Noise in the input data typically reduces the accuracy of the reconstructed pressure fields, but none of the techniques was found to be critically sensitive to the amount of noise added in the present test case, Aerodynamics

A new time-resolved PIV (TR-PIV) method is introduced by integrating both two concepts, the fluid parcel tracking [1] and the ensemble averaged correlation [2, 3]. The dynamic range is extended by applying the polynomial trajectory as the fluid motion [1]. The tracking procedure is not performed by using individual locations of the fluid parcel along the time, but the ensemble averaged cross-correlation value of the trajectory. The random errors caused by the crosscorrelation maps could be then reduced. Each polynomial coefficient is considered individually for economizing the computational cost by introducing the V-cycle search [4]. To taking into account the curved fluid motion, a new iterative corrector based on the shear rate of deformed image according to the trajectory is proposed for stabilizing the process. Not only the present method, but also the state-of-the-art TR-PIV methods, such as the trajectory correlation method [1] and the multi-frame pyramid correlation method [3] are carried out for the comparison. The quantitative evaluations are performed by analyzing synthetic image sequences of translation and rotation motions. An experimental image sequence of the flow around an airfoil is obtained by the High Rate-PIV measurement system, and used to evaluate the performances of the methods. The material acceleration from each methods is also calculated from the trajectory profile or the spatial velocity derivatives with respect to the measurement grid.

The increasing interest for high repetition rate global optical measurement techniques such as Time-Resolved Particle Image Velocimetry (TR-PIV) raises a number of questions concerning their ability to provide relevant statistical and spectral quantities. In an effort to address this issue, complementary TR-PIV and Laser Doppler Velocimetry (LDV) measurements have been carried out. An application to the analysis of the detached flow over a NACA 0015 airfoil at a Reynolds number Re=105 in a water tunnel is proposed.

A three-dimensional (3D) particle image velocimetry (PIV) measurement technique capable of simultaneously monitoring 3D fluid flows and the structure of an arbitrarily moving surface embedded in the flow was proposed with a heavy emphasis on image processing methods [1]. The costs associated with the experimental apparatus were reduced by recording the surface and the trace particles at one image plane without the use of additional cameras or illumination devices. An optimal exposure time for surface and particle imaging was identified using red fluorescent tracer particles in conjunction with a long-pass glass filter. The particle image and surface image were then separated using an image separation process that relied on the feature scaling differences between the particles and the surface texture. A feature detection process and a matching process facilitated estimation of the 3D surface points, and the 3D surface structure was modeled by Delaunay triangulation. The particle volume reconstruction algorithm constrained the voxels inside the surface structure to zero values to minimize ghost particle generation. Volume self-calibration [2] was employed to improve the reconstruction quality and the triangulation accuracy. To conserve computing resources in the presence of numerous zero voxels, the MLOS-SMART reconstruction [3] and the direct non-zero voxel cross-correlation method [3] were applied. Three-dimensional experiments that modeled the flows around an eccentric rotating cylinder and a flapping flag were conducted to validate the present technique.