Velocity Estimate from Schlieren Flow Visualization

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SUMMARY

The discussion focuses on estimating airflow velocity using Schlieren flow visualization techniques. Jagadeesh R replicated a setup using a convex lens, LED light source, and a Moto G4 Plus smartphone camera. While Schlieren visualization primarily measures variations in the index of refraction, it can be adapted for velocity estimation through frame-to-frame comparisons of moving features. However, for more accurate results, particle image velocimetry is recommended as a more reliable method for measuring turbulent flows.

PREREQUISITES
  • Understanding of Schlieren flow visualization techniques
  • Familiarity with convex lens properties and setup
  • Basic knowledge of frame-to-frame image analysis
  • Awareness of particle image velocimetry (PIV) principles
NEXT STEPS
  • Research how to implement particle image velocimetry (PIV) for airflow measurement
  • Explore advanced Schlieren visualization techniques for flow analysis
  • Learn about frame-to-frame image comparison methods for velocity estimation
  • Investigate the use of lightweight particles for enhanced Schlieren imaging
USEFUL FOR

Researchers, engineers, and hobbyists interested in fluid dynamics, particularly those utilizing Schlieren visualization for airflow analysis and velocity measurement.

jagadeeshr
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Hi,

I recently came across a blog on schlieren visualization (http://ottobelden.blogspot.in/2010/07/homemade-schlieren-photography-setup.html).

I replicated it with the following: Convex lens (130 mm dia and 350 mm focal length), LED light source (5 mm white LED) and smartphone camera (Moto G4 Plus).

Below is the flow visualization of a hair dryer:



Can anyone suggest how to estimate the velocity of the air flow?

Thank you
Jagadeesh R
 
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jagadeeshr said:
Can anyone suggest how to estimate the velocity of the air flow?
With suspended particles and hi-speed camera?
 
A.T. said:
With suspended particles and hi-speed camera?
Hi,

Thanks for the reply.

I'll try to suspend aluminium foil or other light weight objects in front of the dryer. For calculations, should I be familiar with any equations?
 
jagadeeshr said:
Hi,

I recently came across a blog on schlieren visualization (http://ottobelden.blogspot.in/2010/07/homemade-schlieren-photography-setup.html).

That's clever! Schlieren isn't really set up to measure velocities, it's more to measure variations in the index of refraction (often be due to temperature and/or pressure variations). To get velocity information, you could simply do a frame-to-frame comparison of the moving features and generate a velocity field from that- but there are a lot of technical issues I've skipped that you must address before claiming that you are actually measuring a velocity.
 
Schlieren velocimetry does exist, but usually for turbulent flows so that you can track the movement of small flow structures. Even then it's not very commonly used because particle image velocimetry is much more reliable.