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van Nieuwburg, W.C.A.M. (author), van Spreuwel, B.J.J. (author), Tran, Minh Tâm Kevin (author), Yang, M.D. (author), Greidanus, A.J. (author), Mulder, G. (author), Tummers, M.J. (author), Westerweel, J. (author), Suijker, W. (author), van Wijk, R. (author)The principal aim of the work presented here is to investigate and demonstrate that a forward tilted rowing blade would result in a more efficient and effective motion of the blade through the water that would result in a higher boat speed when an equal input power is provided. A 1:5 scaled rowing boat is used to determine the performance of...journal article 2023
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Reijtenbagh, J. (author), Westerweel, J. (author), van de Water, W. (author)In our experiment a vortical flow behind a traveling plate turns into turbulence. By exactly repeating this experiment 42 times with a robot, we study the statistics of this transition. In each realization the fate of the flow is followed over 1.7 s when the plate travels with a constant velocity. It suddenly turns turbulent at a scaled...journal article 2023
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Oldenziel, G. (author), Sridharan, S. (author), Westerweel, J. (author)In this paper are presented PIV measurements of turbulent pipe flow at bulk Reynolds numbers Re <sub>D</sub> between 3.4 × 10 <sup>5</sup> and 6.9 × 10 <sup>5</sup> . So-called single-pixel correlation is applied that yields a superior spatial resolution that is slightly larger than the equivalent size of a pixel in the flow. The location and...review 2023
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Reijtenbagh, J. (author), Tummers, M.J. (author), Westerweel, J. (author)We report results on the instantaneous drag force on plates that are accelerated in a direction normal to the plate surface, which show that this force scales with the square root of the acceleration. This is associated with the generation and advection of vorticity at the plate surface. A new scaling law is presented for the drag force on...journal article 2023
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Tummers, M.J. (author), Schenker, M.C. (author), Delfos, R. (author), Twerda, A. (author), Westerweel, J. (author)Measurements were conducted in the fully developed turbulent flow in a pipe with internal diameter D at a Reynolds number of Re <sub>D</sub>= 1.6 × 10 <sup>5</sup> . The pipe walls were equipped with regularly spaced square ribs of relative height h/ D= 0.154 , while the pitch-to-roughness height was varied between p/ h= 1.67 and p/ h= 6.67 ....journal article 2023
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Cornel, W.A. (author), Westerweel, J. (author), Poelma, C. (author)Abstract: A novel experimental imaging-based method is presented for the non-intrusive determination of shock wave characteristics (i.e. shock wave speed and magnitude, and shock-induced liquid velocity) in a bubbly flow solely from gas bubble velocities. Shock wave speeds are estimated by the relative motion between gas bubbles at two...journal article 2023
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van Meerkerk, M. (author), Poelma, C. (author), Hofland, Bas (author), Westerweel, J. (author)We present an experimental study on the gas flow field development over a plunging breaking wave prior to impact on a vertical wall. The variability of wave impact pressure over repeated measurements is well known (Bagnold, 1939). The formation of instabilities on the wave crest are postulated to be the main source of impact pressure variability...journal article 2022
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Westerweel, J. (author), Sridharan, S. (author), Oldenziel, G. (author)In this paper we present PIV measurements of turbulent pipe flow at Reynolds numbers between 3.4×10<sup>5</sup> and 6.9×10<sup>5</sup>. We apply a so-called 'single-pixel correlation' that yields a superior spatial resolution (Westerweel et al., 2004). We use the location and shape of the averaged correlation peak to obtain the mean velocity...conference paper 2022
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Greidanus, A.J. (author), Delfos, R. (author), Picken, S.J. (author), Westerweel, J. (author)The interaction between a turbulent boundary layer flow and compliant surfaces is investigated experimentally. Three viscoelastic coatings with different material stiffnesses are used to identify the general surface response to the turbulent flow conditions. For the softest coating, the global force measurements show two obvious regimes of...journal article 2022
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Fiscaletti, D. (author), Ragni, D. (author), Overmars, E.F.J. (author), Westerweel, J. (author), Elsinga, G.E. (author)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...journal article 2022
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Van Hout, R. (author), Hershkovitz, A. (author), Elsinga, G.E. (author), Westerweel, J. (author)A combination of time-resolved tomographic particle image velocimetry, refractive index matching technique and machine vision algorithms was used to measure the translational and rotational motion of freely moving, nearly neutrally buoyant spheres in a fully developed turbulent boundary layer (TBL). Located in the buffer and logarithmic...journal article 2022
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Reijtenbagh, J. (author), Tummers, M.J. (author), Westerweel, J. (author)We present results on the instantaneous drag force acting on a rectangular plate that accelerates in a direction normal to the plate surface. Conventionally the drag force on an accelerating object is divided into a steady state term and an added mass term, which can both be time-dependent. However, for prolonged accelerations this theory...conference paper 2022
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Nanda, S. (author), Westerweel, J. (author), van Terwisga, T.J.C. (author), Elsinga, G.E. (author)Following their inception, vortex cavities emanating from stationary wing tips in cavitation tunnels are often observed to grow. These effects are usually attributed to the free and dissolved non-condensable gases in the liquid. However, a detailed mechanism for the cavity's growth is not known. Consequently, the repeatability of vortex...journal article 2022
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Van Rijn, Cees J.M. (author), Westerweel, J. (author), Van Brummen, Bodjie (author), Antkowiak, Arnaud (author), Bonn, Daniel (author)Small conical-shaped jets may emanate from a liquid bath a short while after a small drop has hit a liquid pool. Here we perform Particle Image Velocimetry (PIV) measurements of the liquid flow inside upward jets after drop impact and show that fluid elements inside the jets may decelerate up to 5-20 times the gravitational acceleration. The...journal article 2021
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Eisma, H.E. (author), Westerweel, J. (author), van de Water, W. (author)A scalar emanating from a point source in a turbulent boundary layer does not mix homogeneously, but is organized in large regions with little variation of the concentration: uniform concentration zones. We measure scalar concentration using laser-induced fluorescence and, simultaneously, the three-dimensional velocity field using tomographic...journal article 2021
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Reijtenbagh, J. (author), Westerweel, J. (author), van de Water, W. (author)We study the relation between large-scale structures in the concentration field with those in the velocity field in a dye-seeded turbulent jet. The scalar concentration in a plane is measured using laser-induced fluorescence. Uniform concentration zones of an advected scalar are indentified using cluster analysis. We simultaneously measure...journal article 2021
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Mießner, Ulrich (author), Helmers, Thorben (author), Lindken, Ralph (author), Westerweel, J. (author)In this study, we reconstruct the 3D pressure field and derive the 3D contributions of the energy dissipation from a 3D3C velocity field measurement of Taylor droplets moving in a horizontal microchannel (Ca c= 0.0050 , Re c= 0.0519 , Bo = 0.0043 , λ=ηdηc=2.625). We divide the pressure field in a wall-proximate part and a core-flow to describe...journal article 2021
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van den Berg, Joris (author), Bazuin, Rens (author), Jux, Constantin (author), Sciacchitano, A. (author), Westerweel, J. (author), van de Water, W. (author)Abstract: Our quest is for the thumb and finger positions that maximize drag in front crawl swimming and thus maximize propulsion efficiency. We focus on drag in a stationary flow. Swimming is in water, but using Reynolds similarity the drag experiments are done in a wind tunnel. We measure the forces on real-life models of a forearm with...journal article 2021
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Grift, E.J. (author), Tummers, M.J. (author), Westerweel, J. (author)This paper presents the results of the time resolved flow field measurements around a realistic rowing oar blade that moves along a realistic path through water. To the authors' knowledge no prior account of this complex flow field has been given. Simultaneously with the flow field measurements, the hydrodynamic forces acting on the blade...journal article 2021
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Mießner, Ulrich (author), Helmers, Thorben (author), Lindken, Ralph (author), Westerweel, J. (author)Abstract: This paper presents a µPIV measurement of the 3D2C velocity distribution of Taylor droplets moving in a square horizontal microchannel at Ca<sub>c</sub>= 0.005 and Re<sub>c</sub>= 0.051. We reconstruct the third velocity component and present an accuracy assessment of the reconstruction based on a volume flow balance of the 3D3C...journal article 2020