Browsing by Author "Lincoln, Daniel"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Development and characterization of an inexpensive LED-based light source for high-frame-rate schlieren imaging
    (AIAA, 2015) Lincoln, Daniel; Murari, Kartkik; Johansen, Craig
    This work presents characterization results of a 623 nm light emitting diode (LED) based light source developed for low-cost, high frame rate schlieren imaging. The LED was overdriven up to 20 times the rated current while generating 100 ns pulses at a 1 MHz repetition rate. Circuit response, pulse train characteristics, and temperature effects were observed over a large range of input voltages. Relative brightness data was measured with a photodiode and further examined within a schlieren system. Flow visualization of a decaying Mach 3 shock wave were obtained with the system. The wave was produced in a shock tube facility used for aerodynamic measurements. The effect of the light source on image quality, including motion blur are analyzed. Furthermore, shock velocity measurements obtained from the schlieren images are reported.
  • Thumbnail Image
    ItemOpen Access
    Development and Characterization of an LED-Based Light Source for High-Speed Schlieren Imaging
    (2016-02-03) Lincoln, Daniel; Johansen, Craig; Murari, Kartikeya; De Visscher, Alex; Morton, Chris; Wood, David
    This work investigates the viability of using a cost effective, 623 nm light emitting diode (LED) based light source for high-speed schlieren imaging. The pulser circuit used to drive the LED was characterized on the basis of input response, pulse train characteristics, and pulse energies. Relative brightness data was measured with a photodiode and further examined within a schlieren system. Flow images of decaying, cylindrical shocks were obtained with the LED system and benchmarked against a high intensity discharge (HID) lamp. It was found that the LED could be overdriven up to 20 times the rated current while generating down to 100 ns pulses at up to a 1 MHz repetition rate. Moreover, although the LED system produced higher signals and reduced exposure times, similar image detail was observed for each light source. However, the LED exhibited a distinct advantage over the HID lamp in terms of image blur.
  • Thumbnail Image
    ItemOpen Access
    Performance evaluation of an overdriven LED for high-speed schlieren imaging
    (Journal of Visualization, 2015-02) Wilson, Steven; Gustafson, Garrett; Lincoln, Daniel; Murari, Kartik; Johansen, Craig
    A quantitative comparison of an overdriven light-emitting diode (LED) and a high-intensity discharge (HID) lamp as illumination sources for high-speed schlieren imaging is presented. A custom pulser circuit utilizing a new and improved driver circuit was developed to overdrive the LED by a factor of ten while simultaneously reducing pulse widths to sub-microsecond durations. The LED system has been developed as a simple and inexpensive alternative light source to discharge lamps and pulsed laser systems, which are typical for high-speed schlieren imaging. Image quality of a decaying spherical shock wave, produced from the unsteady release of an under-expanded helium jet, is analyzed to assess comparative performance. The effects of framing rate, camera exposure time, and pulse duration on image quality were assessed and compared for the novel LED and an HID. Framing rates of 10,000 and 50,000 fps and exposure times of 1 and 10 µs were tested. Image quality was assessed qualitatively through side-by-side comparisons of fluid dynamic features such as the resolution of shock waves, compression waves, and shear layers. Quantitative analysis was performed through the comparison of the signal-to-noise ratio at the various conditions. LED performance was found to be superior when imaging fast events and inferior when imaging slower events. Results and potential system improvements indicate that the LED system is ideal for low-cost, high-speed flow imaging.