Near-wake analysis of perforated disks with varying hole topology

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Porous disks are encountered in multiple applications such as fluidic damping and chemical mixing and are commonly used in experimental studies pertaining wind turbines and parachute deployment. Although it is commonly assumed that solely porosity dictates the disk’s associated drag coefficient, experimental studies presented within this paper have indicated both porosity and hole topology to be pivotal and an explicit relation is derived. To further understand the underlying flow dynamics, near-wake surveys have been performed on a variety of perforation layouts using two component Laser Doppler Velocimetry, two-component Particle Image Velocimetry and Hot-wire anemometry. Based on the evolution in downstream centerline velocity deficit the ensemble of tested disks could be grouped in 5 categories. For disks with a pore-spacing to disk radius below 0.01 individual jets would merge along the centerline eliminating the appearance of the typical rear stagnation point and with features distinct from those encountered in studies related to planar parallel jet merging. Despite the potential absence of an encapsulated near-wake in the temporal averaged velocity field, spectral analyses of the collected velocity data have evidenced the
existence of a near constant low frequency near-wake motion for all disk tested and a larger scale motion related to vortex shedding which increases in frequency in a near quadratic tendency with porosity. Furthermore, probability
distributions of velocities for lower porosities show clear signs of bi-modality caused by this low frequency motion.
The near-wake velocity field remains highly random in 3 dimensions with strong coupling between the shear-layers
originating from the disk circumference and pore jets, making it impossible to distinguish dominant modes.
Nevertheless, mean velocity fields illustrate the complexity of the near-wake with the presence of flow features
involving multi recirculation zones and axial a-symmetry depending on porosity and pore topology.
Original languageEnglish
Publication statusPublished - 7 Jul 2016
Event18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics - Lisbon, Portugal
Duration: 4 Jul 20167 Jul 2016


Conference18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics
Internet address


  • near-wake
  • porosity
  • disk
  • drag
  • LDA
  • PIV


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