STEP-BY-STEP INSTRUCTION FOR EXAMPLE 6

 

This image group consists of 1022 pairs of PIV recordings for measuring the xy-plane wake flow of a flat plate (L=1.2m), which is vertically towed in the IIHR towing tank at a speed of Uc=1.37 m/s. The laser light sheet is parallel to the water surface at depth of z/L=-0.0833. The measurement area includes the trail edge of the flat plate (x/L=1.00, y/L=0). The PIV image pairs are taken with a DANTEC towed PIV system with a frame rate of 7.5 HZ, and the time interval in each recording pair is 650 microseconds. The view area of the CCD Camera in the measurement plane is 74.7-mm x 75.4-mm. This measurement area is resolved with 1008x1018 pixels in the digital recording. Note that the sample recording pairs are only small portions of the original recordings. More details of the experiment can be obtained from paper “Biases of PIV measurement of turbulent flow and the masked correlation-based interrogation algorithm “ (Gui et. al., 2001, Exp. Fluids 30: 27-35). The evaluation of this image group can be done in following steps:

Step 1: Create image file list

- Execute file “Edpiv.exe” - The start window is shown on the screen;

- Select menu “Edit \ File list” - Dialogue box “Creating file list” appears;

- Press “Input files” button - Dialogue box “Data file list” appears;

- Browse hard drives to find folder “…\ PIVsamples \ 6_TurbulentFlow\ ”;

- Select one of the Windows Bitmap (BMP) files, and then press “Open” button;

- Press “Output file” button - Dialogue box “Data file list” appears again;

- Browse the hard drives to find an empty folder;

- Type in a name for the file list, and then click “Save” button;

- Set “Recording type” to 2

- Click menu “Create” to generate the image file list;

- Close the dialogue box to return to the start window.

Step 2: Open the image group

- Click menu “File \ Image group” - Dialogue box “Recording group” appears;

- Browse the file system to find the image file list created in step 1;

- Press “Open” button - The first image of the first pair is shown in the picture frame.

Step 3: Determine imaging scale and time interval

- Click menu “Edit / Scale & time” in the start window to open dialogue box “Imaging scale / time interval”;

- Select radio button mm;

- Input 74.7 in edit box “Reading on ruler”;

- Input 1008 in edit box “Corresponding pixels”;

- Input 650 in edit box “Time interval [mu-s]”;

- Press “OK” button to return to start window.

Step 4: Setup evaluation parameters

- Click menu “Edit / Evaluation settings” in the start window to open the “Evaluation settings” window;

- Setup parameters as follows
Method & algorithm:
PIV
Ellipse window: Selected
Recording mode:
Recording group: individual evaluation
Exposure type:
Single
Flow type:
One phase
Initial window shift:
(X,Y), X=0, Y= -8.0
Interrogation grid:
16x16
Error limits:
Dx=1.5, Dy=3
Iteration number:
0 (Initial), 6 (Final) 
Window width :
32 (Initial), 32 (Final)
Window height :
32 (Initial), 32 (Final)
Search radius:
12

- Close “Evaluation settings” window.

Step 5: Evaluate the PIV recording pairs

- Press button “Evaluation” in the start window;

- Click menu “Start” in “Evaluation” window;

- Answer “Yes” to question “Do you want to start an evaluation?”

- Set “Start number” and “End number” as 1 and 1022, respectively and press “OK” button in dialogue box “Group evaluation”;

- Wait until the evaluation is completed;

- Press button “OK” to close the dialogue box that notices the end of the evaluation;

- Close “Evaluation window”.

Step 6: Generate data file list

- Select menu “Edit \ File list” - Dialogue box “Creating file list” appears;

- Press “Input files” button - Dialogue box “Data file list” appears;

- Browse the file system in the hard drives to find the folder that contains the image file list;

- Set “Files of type” to “Data files [*.dat]”;

- Select one of the vector map (DAT) files in the folder, and then press “Open” button;

- Press “Output files” button - Dialogue box “Data file list” appears again;

- Browse the hard drives to find a desired folder;

- Type in a file name for the data file list, and then press “Save” button;

- Click menu “Create” to generate the data file list;

- Close the dialogue box to return to the start window.

Step 7: Load vector maps

- Press button “Evaluation” in the start window - “Evaluation” window is opened;

- Click menu “File \ Load vector map” - Dialogue box “Import evaluation data” appears;

- Set “Files of type” to “Task Files [*.tsk]”;

- Browse the file system to find the data file list (TSK file) created in step 6;

- Press “Open” button to start data import;

- Press “OK” button in the information box that notices the end of data import.

Step 8: Conduct statistical analysis

- Select menu “Edit \ Accept results \  valid + corrected”;

- Select menu “Tools \ Statistics - dialogue box “Vector-map/image number” appears;

- Determine start and end numbers of vector maps used for the statistical analysis (e.g. 1 and 1022) and then press “OK” button in the dialogue box.

Step 9: Output statistical analysis results

- Click menu “File \ Save data” - Dialogue box “Save evaluation results” appears;

- Find a desired folder, type in a file name in the dialogue box;

- Press button “Save” to complete the saving procedure.

Step 10: Plot vector map

- Close EDPIV;

- Use TECPLOT to make plots.

 

Mean flow:

 

Normal stress uu:

Normal stress vv: