What the camera actually measures is the Rayleigh scattering signal from the propane. A pulsed Nd:YAG laser serves as the light source. The laser beam is formed into a sheet that cuts through the jet across the camera's field of view with the amount of light scattered toward the camera being proportional to the propane concentration. The measurement area here is in the far-field of the turbulent jet (i.e. well downstream of the jet nozzle), where the Reynolds number is about 4000. The spots that you see here-and-there in this and the following image are due to stray dust particles in the flow, which scatter light much more effectively than the propane molecules.
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Cryocam Model: T5BF1245 Exposure time: 10 ns laser pulse Image size: 300 x 500 pixels (600 x 1000 pixels binned 2 x 2) Area Imaged: 1.8 x 3 cm Pseudo color and color bar were created in post processing. Courtesy of the University of Texas at Austin |
This image is the scalar dissipation rate field calculated from the scalar field of the image above. The scalar dissipation rate is found from the derivatives of the scalar field, by adding the squares of the x and y derivative components. Put another way, it's the squared magnitude of the scalar gradient vector. The scalar dissipation rate measures the amount of molecular mixing in the flow.
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Area Imaged: 1.8 x 3 cm Pseudo color and color bar were created in post processing. Courtesy of the University of Texas at Austin |