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An assessment of high-power light-emitting diodes for high frame rate schlieren imaging

Willert, Christian and Mitchell, Daniel M. and Soria, Julio (2012) An assessment of high-power light-emitting diodes for high frame rate schlieren imaging. Experiments in Fluids, 53 (2), pp. 413-421. Springer Verlag. DOI: 10.1007/s00348-012-1297-1. ISSN 0723-4864.

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Official URL: http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1007/s00348-012-1297-1

Abstract

The feasibility of using high-power light-emitting diodes (LED) as a light source for high frame rate schlieren imaging is investigated. Continuous sequences of high-intensity light pulses are achieved by overdriving the LED with current pulses up to a factor of ten beyond its specifications. In comparison to commonly used pulsed light sources such as gas discharge lamps and pulsed lasers, the pulsed LED has several attractive advantages: the pulse-to-pulse intensity variation is on the same order of magnitude as the detector (camera) noise permitting quantitative intensity measurements. The LED’s narrow emission bandwidth reduces chromatic abberations, yet it is spectrally wide enough to prevent the appearance of speckle and diffraction effects in the images. Most importantly, the essentially lag-free light emission within tens of nanoseconds of the applied current pulse allows the LED to be operated at varying frequencies (i.e., asynchronously), which generally is not possible with neither lasers nor discharge lamps. The pulsed LED source, driven by a simple driver circuit, is demonstrated on two schlieren imaging setups. The first configuration visualizes the temporal evolution of shock structures and sound waves of an under-expanded jet that is impinging on a rigid surface at frame rates of 500 kHz to 1 MHz. In a second application, long sequences of several thousand high-resolution images are acquired on a free jet at a frame rate of 1 kHz. The low-intensity fluctuation and large sample number allow a reliable computation of two-point correlation data from the image sequences.

Document Type:Article
Title:An assessment of high-power light-emitting diodes for high frame rate schlieren imaging
Authors:
AuthorsInstitution or Email of Authors
Willert, Christianchris.willert@dlr.de
Mitchell, Daniel M.Monash University
Soria, JulioMonash University
Date:5 April 2012
Journal or Publication Title:Experiments in Fluids
Refereed publication:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:53
DOI:10.1007/s00348-012-1297-1
Page Range:pp. 413-421
Publisher:Springer Verlag
ISSN:0723-4864
Status:Published
Keywords:high speed imaging, flow visualization, schlieren, density gradient, pulsed light source, light emitting diode
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:Propulsion Systems
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Virtual Engine and Validation Methods
Location: Köln-Porz
Institutes and Institutions:Institute of Propulsion Technology > Engine Measurement Systems
Deposited By: Dr.phil. Christian Willert
Deposited On:22 Aug 2012 11:18
Last Modified:26 Mar 2013 13:39

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