This dataset is that of the 1st Challenge on Lagrangian Particle Tracking (LPT) and Data Assimilation (DA), co-organized in 2020 by Benjamin Leclaire (ONERA), Andrea Sciacchitano (TU Delft) and Andreas Schröder (DLR), within the European Union funded project HOMER (Horizon 2020 research and innovation program, grant agreement No. 769237). Data have been made open to participants on March 9th, 2020, with a requested submission of results by July 17th, 2020. Results have been presented during the 3rd workshop on CFD and DA for PIV and LPT, held online on November 19-20, 2020, as well as during the 14th International Symposium on Particle Image Velocimetry - ISPIV 21.

Physical situation

In order to address a flow configuration with significant turbulent structures, and large enough pressure fluctuations on the solid walls, the wake of a cylinder in ground effect is considered in that test case. Coordinate system is defined with X the streamwise, Y the spanwise and Z the wall-normal directions, respecting the right-handed rule. The cylinder has a diameter of 10 mm and its centre is located 15 mm above the wall, thus creating a gap of 10 mm. Flow numerical simulation is performed by Monotone Integrated Large Eddy Simulation, using the ONERA HPC solver FASTS. The boundary layer upstream of the cylinder is fully turbulent, with a thickness of 60 mm and a momentum thickness Reynolds number of 4,150, probed ten diameters upstream of the cylinder. The medium considered is water, and the bulk velocity is U_∞=0.667 m/s. Figure 1 illustrates the turbulent structures and wall pressure fluctuations on a flow snapshot, while Figure 2 provides information on mean flow velocity. More details can be found in Leclaire et al. (2021).

Figure 1 - Time evolution of the LES flow simulation, including Q-criterion iso-surfaces color-coded by streamwise velocity u, iso-contours of pressure p at the lower and side walls

 

Figure 2 - Streamwise mean and fluctuating velocity components, with averaging performed in time and span. Profiles on the right correspond to streamwise locations identified by the vertical dashed lines in the left figures

To build the LPT and DA datasets, a cloud of virtual particles, hypothesized as fully passive tracers and initially located at random positions in space, has been propagated within the simulation, by interpolating the LES velocity field.

Domain of interest and setup

Figure 3 - Schematic of the location and extent of the measurement domain, together with the definition of the coordinate system

As depicted in Figure 3, the region of interest for the challenge starts 35 mm downstream of the cylinder centre, and is a parallelepipedic domain of 100 mm×50 mm×30 mm (streamwise × spanwise × wall-normal). In span, it is centred and covers half of the numerical domain; in the wall-normal direction, it starts at the lower wall.

The virtual setup consists of illumination with a limited extension in the streamwise and wall-normal directions (simulating the use of a slab) and a set of four cameras viewing the measurement volume mainly from above (Z-direction) onto the XY-planes. The cameras are located along the X axis at Y=0 at a height of about Z=600 mm with a viewing angle of (+30,+10,-10,-30) degrees relative to the Z axis. Each camera sensor is made of 1920 x 1200 pixels with a 10 µm pitch. Pixel position (0,0) corresponds to the centre of the pixel located at the top left corner of an image. The calibration parameters correspond to a basic camera pinhole model with focal length f=100 mm without any extra optical distortion.

Camera calibration can be performed by using the ASCII file CalibPoints.txt (download button also available on the LPT, Two-Pulse page).

References

Leclaire, B., Mary, I., Liauzun, C., Peron, S., Sciacchitano, A., Schröder, A., ... & Champagnat, F. (2021). First Lagrangian Particle Tracking and Data Assimilation challenge: datasets description and evolution to an open online benchmark. In Proceedings of 14th International Symposium on Particle Image Velocimetry (Vol. 1, No. 1, pp. 1-2). ILLINOIS Tech/Paul V. Galvin Library.