Projected Background-Oriented Schlieren Imaging

The Projected BOS imaging system provides a significant advancement over other BOS flow visualization techniques. Specifically, the present BOS imaging method removes the need for a physically patterned retroreflective background within the flow of interest and is therefore insensitive to the changing conditions due to the flow. For example, in a wind tunnel used for aerodynamics testing, there are vibrations and temperature changes that can affect the entire tunnel and anything inside it. Any patterned background within the wind tunnel will be subject to these changing conditions and those effects must be accounted for in the post-processing of the BOS image. This post-processing is not necessary in the Projected BOS process here. In the Projected BOS system, a pattern is projected onto a retroreflective background across the flow of interest. The imaged pattern in this configuration can be made physically (a pattern on a transparent slide) or can be digitally produced on an LCD screen. In this projection scheme, a reference image can be taken at the same time as the signal image, facilitating real-time BOS imaging and allowing the pattern to be changed or optimized during measurements. The Projected BOS imaging technology has been proven to work by visualizing the air flow out of a compressed air canister taken with this new system. The Projected BOS is available for patent licensing. Inventors at NASA's Langley Research Center (LaRC) have developed a new background-oriented schlieren (BOS) imaging technique. The new technique enables vibration-tolerant, real-time, and reference-free BOS imaging for scientific investigations or industrial flow monitoring. Typically, BOS imaging requires a physical pattern on a retroreflective surface within the flow of interest to visualize that flow through changes in the pattern due to density changes between the pattern and a camera. Here, the BOS imaging technique does not require a physical pattern within the flow, and it is instead projected through the flow onto a retroreflective surface and imaged by a camera. Projecting the pattern allows the pattern to be changed mid-measurement and reduces the cost of BOS imaging for a variety of flow visualization applications.