2nd LPT Challenge Case 2 Datasets
Physical situation
The physical situation is that of the wake caused by two cylindrical pillars placed in a turbulent boundary layer. The flow medium is air, and its bulk velocity outside the boundary layer is equal to 10 m.s-1. At the streamwise position of the cylinders, the boundary layer is approximately 60 mm thick, with a momentum Reynolds thickness equal to 4,150. Numerical simulation is performed using Monotone Integrated LES, wherein embedded propagation of virtual particles, hypothesized as fully passive tracers, is included.
Axes X, Y and Z respectively correspond to the streamwise, spanwise and wall-normal directions (see Figure 2). Simulation is performed over an extension of 100 mm in Y, with spanwise boundary conditions. Cylinders have a diameter of 10 mm and their centres are located 25 mm from the simulation spanwise edges. For the challenge, different domains of 30 mm thickness (Z direction), starting 10 mm downstream from the cylinder centres, have been selected.
The optical setup consists of four virtual cameras which view these domains mainly from above (Z direction), onto the XY plane. They are located at the base of a square pyramid, at a height of around 0.45 m (Z direction). Edges of this base are along the X and Y axes and the edge size is equal to 0.6 m. All cameras have a 2048 x 2048 sensor with 10 µm pixel pitch, and are equipped with an f = 200 mm lens.
Among the varying parameters in this case is the ratio I/U between the volume of the intersection of the cameras' fields of view (denoted by I) and of their union (denoted by U). Value of this parameter determines whether all of the illuminated domain (and particles) are viewed by all cameras (I/U = 1), or if parts of the domain/particles are viewed only by a subset of them (I/U < 1). As depicted in Figure 2, the domain extensions in X and Y directions change depending on the I/U value: the domain is largest for I/U = 0.46, and smallest for I/U = 0.99, which are respectively the smallest and largest values for the I/U parameter in the dataset. The origin O of the coordinate system changes accordingly, as it is always supposed to be located at the centre of the domain in the X and Y directions, and at the wall (Z direction). As the camera system also adapts to the different domains, i.e. always has the same location relatively to the origin O, this allows to consider the same calibration for all cases. Note also that, in order to obtain the desired I/U values, illumination had to be cut artificially in both the X and Y directions, for all I/U > 0.46. In a sense, this amounts to using a slab for cutting in X, and to consider wind-tunnels of different spans for cutting in Y.
Input data
Camera calibration
Camera calibration can be performed by downloading the ASCII file LPT_CASE02_CalibPoints.txt (using the Camera Calibration link). Each line of this file contains the coordinate of a point in the domain together with its projection 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 contains both two-pulse (TP) and time-resolved (TR) image sequences. The inter-frame time is fixed at 40 µs. A constant particle image size (PSF/OTF) is used, and some typical camera noise is added on the images. Parameters explored are the seeding density, the I/U value and Mie scattering (Mie = 1 if accounted for, otherwise Mie = 0). Note that Mie scattering coefficients correspond in fact to different observation angles than that of the present setup. Indeed, the current setup would either lead to having a pair of cameras in forward scattering and the second in backward scattering, which is a situation that one would avoid in practice (case of light in the X or Y direction), or to having all cameras with the same scattering conditions (case of light in the Z direction). Instead, equivalent camera positions have been picked coresponding to different angles in the forward scattering domain (close to 30° and 45° relative to incident light).
For both TP and TR acquisition types, the parameter sweep is the following:
- Variation of seeding density for I/U = 0.99 and Mie = 0: densities equal to 0.025, 0.05, 0.08, 0.12, 0.16, 0.20 and 0.25 particles per pixel (ppp)
- Variation in I/U at 0.08 ppp, with Mie = 0: I/U values equal to 0.46, 0.59, 0.72, 0.85 (and 0.99, included in the ppp variation)
- Influence of Mie scattering at 0.08 ppp: cases with Mie = 1 at I/U = 0.99 and 0.46, to be compared with the same with Mie = 0
Images are named in the following format:
LPT_CASE02_YY_ppp_0_AAA_IU_BBB_Mie_D_IEEEE_C.tif, with:
YY: acquisition type (TR or TP)
AAA: fractional ppp value
BBB: value of I/U, multiplied by 100, with a leading 0
D: Mie accounted for (D=1) or not (D=0)
EEEE: snaphot number with leading zeros, starting from 0000
C: camera number, from 0 to 3.
In the TR case, sequences contain 50 images for ppp up to 0.16, and 100 images for higher-density cases.
Requested output and formatting rules
Participants can choose whether they want to process the TR or the TP data, or both. For either acquisition type, results have to be submitted at least up to ppp = 0.12 included; in particular, all cases at 0.08 ppp, including those corresponding to the I/U and Mie sweeps, are mandatory. Processing as well the higher seeded cases is of course encouraged.
Submission form and zip archive
Clicking on "Submit TP results" or on "Submit TR results" will open a form allowing you to upload a file containing your results. In either case, 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
For TP, the single computed flow field corresponding for a given parameter set needs to be supplied in the following format:
ASCII-file with first line
X0 Y0 Z0 X1 Y1 Z1
followed by one line for each particle with the two measured particle positions X0, Y0, Z0 and X1, Y1, Z1 in mm for time steps 0 and 1.
For TR, the tracked particles for time step 25 (images '_I0024', ppp up to 0.16) or 50 (images '_I0049', for ppp larger or equal to 0.2) for a given parameter set need to be supplied in 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 to the estimation of velocity and acceleration) Xfit, Yfit, Zfit in mm, the velocity VX, VY, VZ in m.s-1, and the acceleration AX, AY, AZ in m.s-2, all calculated at time step 25 or 50 depending on the seeding density of the case.
For both TP and TR, naming of each individual result file should follow the convention:
ZZZZ_LPT_CASE02_YY_ppp_0_AAA_IUBBB_Mie_D_PartFieldNN.dat, with:
ZZZZ: algorithm acronym or short name as provided on the submission form (see previous paragraph)
YY: acquisition type (TP or TR)
AAA: fractional ppp value
BBB: value of I/U, multiplied by 100, with a leading 0
D: Mie accounted for (D=1) or not (D=0)
NN: time-step index (24 or 49 depending on ppp for TR, 00 for TP).
Contact in case of questions: Benjamin Leclaire, ONERA: benjamin.leclaire@onera.fr