Particle Image Velocimetry, or PIV, is a technique for flow visualization and velocity measurement. Also frequently encountered in the literature is 'Large-Scale Particle Image Velocimetry', or LSPIV. What are the conceptual and technical differences between PIV and LSPIV? What kinds of applications are they most suitable for? Do they require the same equipment and procedure?
see
Large-scale eddies measured with large scale particle image velocimetry
J.F. Fox, A. Patrick
https://booksc.xyz/book/8681301/f92d05
LSPIV is derived from PIV measurement to observe very large structure such as rivers and more particularly surface runoff.
You can see the PIV technic as the fundamental lab-scale measurement and LSPIV as the large scale measurement. Therefore, the incorporation of seeding particles might not be necessary in that case.
Here you can find another reference:
https://hal.archives-ouvertes.fr/hal-01118478/document
Best regards,
" Do they require the same equipment and procedure? "
Recording the pictures may require different camera types (e.g. PIV often uses high-speed or double-frame cameras, whereas LSPIV can use regular cameras). Additionally, you usually need a laser light source for PIV to illuminate particles, but LSPIV requires only some sort of moving texture.
When you finished recording the images, then the rest (cross-correlation e.g. in PIVlab) is identical.
All the above answers are correct and useful. Probably one major difference that has to be taken into account is due to the different illumination and imaging methods: in PIV you trust the 2D position of the particle from a careful alignment of the laser sheet and the camera (usually 90 deg, thin laser sheet) and in LSPIV you probably will use some natural or white light or LEDs and quasi-2D approximation, and most probably not very well aligned camera. Therefore, I believe a bit different course of analysis and uncertainty estimate is required.
The software is probably identical, as William Thielicke mentioned, so PIVLab (his :)) or OpenPIV (disclaimer - our :)) can be used without modifications. The insight and meaning of the vectors is slightly different due to the experiment construction. Please take a look on 3D-PTV - seems to be a bit more suitable for complex large scale flows with 3D features. Another disclaimer - OpenPTV (ours :)) is also free and open.
There is a big difference that it is often overlooked: the subpixel accuracy.
In standard PIV, particles can be approximated as Gaussians. The cross correlation of patterns of Gaussians yields a Gaussian located in the position of the average displacement. This is what lets the PIV achieve subpixel accuracy using Gaussian interpolation or similar.
This is not the case for LSPIV, for which the subpixel interpolation via 2D Gaussian is usually meaningless. I am not aware of a detailed study on the topic and I would be very happy if you could suggest me some. In general, I would be very tempted to suggest other methods of image interrogation, from the family of optical flows, which do not rely on the classical assumptions used in standard PIV.
I do not see any problem with Gaussian or parabolic interpolation. It works with all kind of particle shapes not necessary Gaussian. Of course optical flow is also possible.
Thank you for your answer Alex. The problem is that the cc map is not at all Gaussian and often has fancy shapes that are not well fitted by a Gaussian. Hence the peak location becomes very ambiguous. I‘ll try to look for an example when I come back from holidays !
Miguel Alfonso Mendez, Alex Liberzon, William Thielicke, Hugo Quintens, and Maged Gumaan Bin-Saad,
I really appreciate your invaluable comments. I'm still uncertain about something: is it feasible to adapt the PIV facilities for measurement using LSPIV with the least modification? I mean, except for the illumination equipment which is, of course, different by each approach, could the rest of facilities (including whether equipment or software) be used in a multipurpose manner? This is important for me because my intended research project entails measurements of both micro (turbulence) and macro scales, for which PIV and LSPIV respectively seem to be suitable.
- Badges
- Science topic
- Similar topics
- Engineering
- Electrical Engineering
- Signal Processing
- Image Processing