Velocity Estimate from Schlieren Flow Visualization

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Discussion Overview

The discussion revolves around estimating the velocity of airflow using schlieren flow visualization techniques. Participants explore methods and considerations related to this experimental approach, including the use of suspended particles and high-speed cameras.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Jagadeesh R describes his setup for schlieren visualization and seeks advice on estimating airflow velocity.
  • One participant suggests using suspended particles and a high-speed camera as a method for estimating velocity.
  • Another participant notes that while schlieren visualization is primarily for measuring variations in the index of refraction, it is possible to estimate velocity through frame-to-frame comparisons, although this involves technical challenges.
  • It is mentioned that schlieren velocimetry exists but is typically used for turbulent flows, with a preference for particle image velocimetry due to its reliability.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of schlieren visualization for measuring velocity, with some suggesting alternative methods and others highlighting the limitations of the technique.

Contextual Notes

Participants indicate that there are technical issues to address when attempting to measure velocity with schlieren visualization, and the discussion includes references to the reliability of different methods for velocity estimation.

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.