Optofluidic devices have revolutionized the manipulation and transportation of fluid at smaller length scales ranging from micrometers to millimeters. We describe a dedicated optical setup for studying laser-induced cavitation inside a microchannel. In a typical experiment, we use a tightly focused laser beam to locally evaporate the solution laced with a dye resulting in the formation of a microbubble. The evolving bubble interface is tracked using high-speed microscopy and digital image analysis. Furthermore, we extend this system to analyze fluid flow through fluorescence-Particle Image Velocimetry (PIV) technique with minimal adaptations. In addition, we demonstrate the protocols for the in-house fabrication of a microchannel tailored to function as a sample holder in this optical setup. In essence, we present a complete guide for constructing a fluorescence microscope from scratch using standard optical components with flexibility in the design and at a lower cost compared to its commercial analogues.@en

The small scales of turbulence in a high-Reynolds-number jet (R e λ≈ 350) are investigated with a µPIV setup to overcome the optical limitations of conventional tomographic PIV setups. With the aim of validating the performances of tomographic long-distance µPIV, analyses are carried out involving statistical aspects of the small scales of turbulence. The technique is assessed and the data are bench-marked to be applied to the analysis of any three-dimensional small-scale phenomena in large-scale flow domains. Graphical abstract: [Figure not available: see fulltext.].@en

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 m ², or 1 × 1 m ², 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.

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We investigate the fluid motion generated by a moving rowing blade. The blade follows a complex path with rather strong acceleration and subsequent deceleration. The blade path is mimicked at a 1:2 scale in a large open-top water tank using a robot system. The tank is transparent, thus enabling full optical access for performing large-field particle image velocimetry (PIV). The robot system allows us to precisely repeat subsequent rowing blade motions. PIV measurements in the same plane show that the fluid motion is highly repeatable, except for the small-scale turbulent fluid motions. When combined with direct measurements of the forces on the rowing blade (Grift et al. 2019a) the PIV data provide insight in the variation of the hydrodynamic forces acting on the blade during motion. This makes it possible to improve the efficiency and effectiveness of the propulsion which is of great relevance to competitive rowing. @en

Time-resolved tomographic particle image velocimetry (PIV) measurements (acquisition rate 250 Hz) were performed in a turbulent boundary layer on the side wall of an open channel, water flow facility (cross section 60 × 60 cm2, W × H), 3.5m downstream of the inlet at a bulk flow velocity of Ub = 0.17m/s (Reb = UbH/ν = 97, 679, δ0.99 = 45.0 mm, Reθ = 752). The measurement volume was a horizontal slab (60 × 15 × 60mm3, l × w × h) extending from the wall, 30 cm above the bottom. The setup comprised four high-speed ImagerPro HS cameras (2016×2016 pixels), a high-speed laser (Nd:YLF, Darwin Duo 80M, Quantronix), optics/prisms, and data acquisition/processing software (LaVision, DaVis 8.2). Data were acquired with and without a stationary held sphere that had a diameter, D = 6mm (D+ = 51, “+” denotes inner wall scaling), and was positioned at x3 = 5.4 and 37.6mm ( = 43 and 306) from the wall (measured from the sphere’s center). Sphere Reynolds numbers based on D and the average streamwise velocity at the sphere’s center were 692 and 959, respectively. The mean streamwise velocity profiles of the undisturbed boundary layer clearly exhibit a canonical shape. Introducing the sphere strongly affected log layer and buffer layer mean velocity and Reynolds stress profiles. Recovery to the undisturbed boundary layer characteristics is faster with the sphere positioned closest to the wall. When positioned at h+ = 306, near-wall, uplifted, coherent vortical structures extend from the wall up to the sphere’s wake with which they interact.@en