Weir Hall 120
Socorro, NM, 87801
A shadowgram of the firing of a sabot-fired rifle round.
We have developed a modern retro-reflective shadowgraph system for the visualization of refractive flows, especially shock wave and heat convection applications. This shadowgraph system uses a 2.4 x 2.4 m retro-reflective screen, white-light arc lamp source, and is compatible with digital cameras. This simple and portable system has been used in a wide variety of experiments both inside and outside of the laboratory.
Hargather, M. J. and Settles, G. S., "Retroreflective shadowgraph technique for large-scale flow visualization," Applied Optics, 48(22):4449-4457, 2009.
The shock wave produced from the explosion of a car
bomb is visualized with the background oriented
The background oriented schlieren (BOS) technique is a new approach to schlieren imaging wherein a refractive disturbance is observed through its distortion of a distant background. BOS uses a computer algorithm to compare an image with no flow disturbance to one with a flow disturbance in order to define the regions where light refractions have occurred. This technique was invented elsewhere by G.E.A. Meier and S. Dalziel, but here we are applying it to large-scale visualizations where traditional optics do not provide a large enough field of view.
Hargather, M. J. and Settles G. S., "Natural-background-oriented schlieren imaging," Experiments in Fluids, 48(1):59-68, 2010.
(A) A focusing schlieren image of a turbulent propane
flame, and (B) the average velocity vector field
calculated through an SIV analysis on 100 image pairs.
The experimental measurement of velocity fields is typically performed using the particle image velocimetry (PIV) technique. This technique "seeds" a flow with small particles and then tracks the motion of these particles to obtain the flow velocity vector field. Some scenarios exist where injecting seed particles is impractical or dangerous, thus "seedless-velocimetry" is desired. For these applications we have developed the technique of schlieren image velocimetry (SIV).
SIV works in a similar manner as traditional PIV, only the particles that are used are naturally-occurring refractive-turbulent eddies in the flow which are made visible through schlieren imaging. Two schlieren images of a flow are recordedb and then the motion of the turbulent eddies is measured as a method of determining the local velocity fields. This technique works well for turbulent flows where density, temperature, or species gradients exist, as in compressible and combustion flows. By using the naturally-occurring refractive-turbulent eddies, we are able to obtain seedless velocimetry with SIV.