Abstract
In this paper the development of a high-power pulsed LED line light and its use to apply particle image velocimetry (PIV) during wave impact measurements are described. An electrical circuit that generates high-current pulses is designed and built, which is used to overdrive a number of commercially available LEDs. The limit for this overdrive-capacity is determined as function of pulse duration for various commercial available LEDs. Two systems of cylindrical convex lenses are designed to act as a collimator and reduce divergence of the LED bundle and the resulting light sheet properties (maximum light intensity and sheet thickness) are investigated. An array of LEDs of 60 cm length (referred to as the LED line light) is designed and manufactured. For the two lens systems, the LED line light provides proper light sheet conditions to illuminate measurement regions in the order of either 0.3 × 0.3 m2, or 1 × 1 m2, at a sufficiently constant light sheet thickness of 5 mm. The application of the LED line light is demonstrated by quantifying the instantaneous flow field of a wave impacting on a blunt object in a wave flume. PIV measurements are conducted at an acquisition rate of 25 frame pairs per second, quantifying maximum flow velocities in the order of 1.0 m s−1 at a LED pulse width of 200 μs. The system, consisting of the LED line light, a CMOS camera and open source PIV processing software provides the possibility to perform 2D planar PIV measurements for a fraction of the costs of a commercially available laser based PIV system.
Highlights
Particle image velocimetry (PIV) is a measurement technique in fluid mechanics to instantaneously quantify a flow at high resolution by determining the displacement of a large number of particles that are assumed to follow the flow
Additional measurements in which the luminosity of a light emitting diodes (LEDs) line light is compared to that of a conventional laser light sheet would be very helpful. Such measurements can give a better indication for the application range under which a LED line light can be applied as light source for particle image velocimetry (PIV) measurements
This work presents the development of a pulsed high power LED line light and its application as a light source to perform PIV measurements in a wave flume
Summary
Particle image velocimetry (PIV) is a measurement technique in fluid mechanics to instantaneously quantify a flow at high resolution by determining the displacement of a large number of particles that are assumed to follow the flow. Concluding, lasers have disadvantages regarding safety, complexity, large field-of-views and the systems are expensive For these reasons, studying the use of alternative light sources for large scale (1 × 1 m2) PIV measurements (i.e. light sources other than (pulsed) lasers) in hydraulic applications is of interest. The ability of LEDs to be overdriven using short duration pulses with currents much higher than prescribed by the manufacturer is described and applied to small scale (50 × 50 mm2) PIV measurements both in air and water (velocities up to 0.5 m s−1) [10] In addition to these studies with single LEDs as light sources, the application of LED light arrays have been investigated as well. Instantaneous data and velocity fields of an impact of a wave on an overhang are shown
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