2nd LPT Challenge Case 1 Dataset
Physical situation
This test case considers the square duct DNS simulations of Pirozzoli et al. (2018), to study a fully developed turbulent flow. The figure below illustrates the simulation results, conducted at a bulk Reynolds number of Reb = 2hub/nu = 40,000 and a friction Reynolds number Retau approximately equal to 1,000, where h denotes the duct half-width, ub is the bulk velocity and nu the fluid’s kinematic viscosity.
For the challenge, a domain of h x h x h is considered, where x denotes the streamwise direction, and y = 0 and z = 0 are the duct walls. A virtual experiment is conducted in water (rho = 1000 kg/m3, nu = 1 . 10-6 m2/s), with h = 100 mm and ub = 0.2 m/s. The experimental setup is sketched below, including the four-camera arrangement for the LPT challenge. A cloud of virtual particles, hypothesized as fully passive tracers, has been propagated within the DNS simulation.
Input data
This test case of the LPT challenge considers four cameras viewing the fully-illuminated measurement region of 100 x 100 x 100 mm. The cameras view the measurement volume mainly from above (z-direction). The cameras (1,024 x ,024 pixels, 10 µm pitch) are located at a height of about z = 1 m with a viewing angle of theta = +/- 30° relative to the z axis. Equipped with f = 105 mm objectives and aiming at the centre of the measurement domain, the full volume is not entirely in view by each camera.
Camera calibration
Camera calibration can be performed by downloading the ASCII file LPT_CASE01_CalibPoints.txt. Each line of this file contains the coordinates of a point in the domain together with its projections on the four cameras:
X Y Z x1 y1 x2 y2 x3 y3 x4 y4
where (X,Y,Z) are the point coordinates in units of mm and (xi,yi) the coordinates of its projection on camera i in units of pixel. Pixel position (0,0) corresponds to the centre of the pixel located at the top left corner of an image.
Cases and images
This test case comprises three different situations, with varying particle displacements in the bulk. The time separation between frames is set to 5.916, 8.283 and 10.649 ms for each case, such that particles at the bulk velocity displace approximately 10, 15 and 20 pixels respectively. For every condition, the seeding density is kept constant at 0.1 ppp. Some typical camera noise is added to the images. A constant particle image size (PSF or OTF) is used. A sequence of 100 frames (starting at frame 0) is provided for each situation, and the images are stored in 16-bit tiff compressed format.
The images are named in the following format:
LPT_CASE01_TR_dtT_IBBBB_C.tif, with:
T: dt value (1, 2 or 3), corresponding to the approximate bulk displacement of 10, 15 and 20 px respectively
BBBB: snapshot number, starting from 0000
C: camera number, from 0 to 3
Requested output and formatting rules
Submission form and zip archive
Clicking on "Submit results" will open a form allowing you to upload a file containing your results. This file should be a zip archive (.zip extension), containing directly (no folder) one result file per seeding density, each being an ASCII file (see further precisions regarding file naming and format in the paragraphs below).
The upload form should also be filled with the following information, which is used for result presentation only if you choose to publish your result based on the evaluation sent by email:
- the short name or acronym of the algorithm used for data processing (should match with the prefix name of your result files, see below). This name should have a length of 24 chars maximum, and contain no space. Authorized chars are alphanumeric chars and one of the following: [ ] _ - @
- the full name of the algorithm. This name should have a length of 100 chars maximum, and should not contain commas.
- Optionally, you may provide the URL address of the publication (if any) about your algorithm, or of a webpage describing it
- If needed (e.g. in the situation where the algorithm is due to a collaboration between two or more institutions), you can correct the name of the Institution which will appear in the public result tables (set by default to your institution). For this field, the maximum length is of 24 chars and commas are not allowed.
Requested data and file format
The zip archive should contain three files, one for each value of parameter dt. Each file should contain information about the flow field for time step 49 (from the sequence starting at 0), using the following format:
ASCII-file with first line
X Y Z Xfit Yfit Zfit VX VY VZ AX AY AZ
followed by one line for each particle track with raw position, X, Y, Z in mm, fitted position (i.e. associated with the estimation of velocity and acceleration) Xfit, Yfit, Zfit in mm, the velocity VX, VY, VZ in m/s, and the acceleration AX, AY, AZ in m/s2.
Naming of the files should be as follows:
XXXXX_LPT_CASE01_TR_dtT_PartField49.dat
where XXXXX corresponds to the acronym / short name of your algorithm (3 characters minimum, no space, only [A-Z0-9a-z]_-@ chars) as indicated in the corresponding field of the upload form (i.e. both should match, including for upper and lower case letters), and T to the dt value (1, 2 or 3), corresponding to the approximate bulk displacement of 10, 15 and 20 px respectively.
Contact in case of any questions: Andrea Sciacchitano, TU Delft: a.sciacchitano@tudelft.nl
References
Pirozzoli, S., Modesti, D., Orlandi, P., & Grasso, F. (2018). Turbulence and secondary motions in square duct flow. Journal of Fluid Mechanics, 840, 631–655. doi:10.1017/jfm.2018.66