Question

In the lecture videos you have seen different techniques to visualize flow field and
gather qualitative and quantitative information flow characteristics. Obtain information
about new laser based techniques for measuring velocity fields. Give some information /
examples of case studies on their usage on following topics at differe nt disciplines using
scientific literature: building aerodynamics, a utomotive a erodynamics , river flow,
offshore structures.
Notes:
This part should not exceed 2 paragraphs . You can use library website to reach
scientific databases and online resources . Cite your references at the end.

Answer 1

Laser based techniques for measuring velocity fields

The laser based techniques such as Particle Image Velocimetry (PIV), Laser Doppler Velocimetry (LDV), Molar Tagging velocimetry allows to detect the fluids velocity in liquids as well as gases. These techniques are non intrusive which means that they dont require sensors.The working rule of a PIV system is simple and the velocity is determined by fundamental principle displacement and time.Using cylindriacal lens two laser pulses are projected into a 2-D sheet. These laser pulses are adjusted to a CCD camera to capture the firing of laser beam. User sets the time seperation between two images and displacement of particle images is measured. The working principle of LDV technique is based on the exposure of the frequency shift of laser light. The laser light has been scattered by small particles.According to the Doppler principle scattered light has frequency shifted. The light bears information about the velocity of the particle.PIV and LDV techniques are based on the concept of visualization of small tracer particles introduced in the flow.

The PIV technique is very useful in aerodynamics research. Because PIV helps to understand the unsteady flow phenomena like shear and boundary layers, wake vortices, and separated flows above models at high angle of attack. It possess spatially resolved measurements of the instantaneous velocity field within a very short time. Also allows the detection of large and small scale spatial structures in the flow.The PIV method was adapted in the specific constraints of high flow conditions of river. Using a usual PIV data processing, significant variations of the water surface elevation were taken into consideration for the image rectification. Non-intrusive flow measurement is used widely in offshore engineering laboratories, mainly in the form of Laser Doppler Velocimetry (LDV). LDV can provide extremely precise measurements which have proved valuable . and these data are essential for the development and validation of numerical hydrodynamic models.

http://www.forbrf.lth.se/english/research/measurement-methods/laser-based-velocity-measurement-techniques-ldv-and-piv/

https://www.sciencedirect.com/topics/engineering/particle-image-velocimetry

https://www.researchgate.net/publication/224784616_Application_of_PIV_in_Large_Wind_Tunnels

https://hal.archives-ouvertes.fr/hal-01016952/document

https://www.onepetro.org/conference-paper/ISOPE-I-95-277