Weekly_4-17 - Weekly Progress Report#9 Background Oriented...

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Weekly Progress Report #9 Background Oriented Schlieren AAE 490R/590R 17 April 2008 Hrs. Worked Landon Baur John Tapee
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Week’s Goals 1) Return to Mach 2 tunnel with prepared PIV procedure and test using backgrounds at different distances (thus changing the sensitivity of the system). Also, use the double wedge model to reduce boundary layer effects. 2) Test the shop nozzle against both aluminum and steel backgrounds. 3) Figure out how to solve for the density field given the density gradient field. Week’s Accomplishments 1) As of Monday of this week, the compressor that maintains high pressure in the outside storage tank at ASL was not operating correctly, which prevented us from running the Mach 2 tunnel to test smaller sensitivities. 2) BOS tests of the shop nozzle against the aluminum background showed a hint of the shock diamonds we would expect, but only a hint. The only reason we could see this general effect is because we knew what to expect, so this by no means represents an arrival as a satisfactory solution for an undergraduate lab. Although the shock structure was difficult to see visually, we hoped that the BOS software could still extract density. As of this writing, we are still unsuccessful at this endeavor. 3) While working towards extracting a density field, several observations arose: a) The filtering algorithm in the PIV code is useful in that it “fixes” any stray vectors; however, it would be best to eliminate these stray vectors by adjusting the initial image correlation process. Adjusting the grid point locations seemed to be a good way of doing so (see more explanation in the detail section). b) Initially, the calculated density gradient vectors pointed in the opposite direction of what was needed, causing the regions of expected high density to be computed as regions of low density (and vice versa). While negating these results is a simple solution for this issue, we believe the problem stems from the non- standard x and y directions defined in the initial image (origin at the top left, x in vertical direction, y in horizontal direction). c) With a fine enough distribution of density gradients, the extracted density field reflect what is expected; however, since we are now using the unsteady candle flame as our baseline image, it is more difficult to predict the density field theoretically. This is one of the reasons that testing in the Mach 2 tunnel again was a high priority this week. Next Week’s Plan 1) If the compressor at ASL is fixed before the end of the week, our plan is to try to find some time to run the Mach 2 tunnel as we had planned for this week. If the tunnel is still inoperable at the end of this week, the time constraints on the remainder of this project will probably preclude any additional tunnel testing. 2)
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Weekly_4-17 - Weekly Progress Report#9 Background Oriented...

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