Between Dec 19, 2024 and Jan 2, 2025, datasets can be submitted to DRUM but will not be processed until after the break. Staff will not be available to answer email during this period, and will not be able to provide DOIs until after Jan 2. If you are in need of a DOI during this period, consider Dryad or OpenICPSR. Submission responses to the UDC may also be delayed during this time.

Browsing by Subject "particle image velocimetry"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Organization And Scaling Of Coherent Structures In The Outer Region Of High-Reynolds-Number Turbulent Boundary Layers
    (2020-05) Heisel, Michael
    Recent advances in high-Reynolds-number turbulence have suggested there is a general self-organization of coherent structures in the logarithmic and wake regions of boundary layer flows. The organization comprises large-scale velocity structures known as uniform momentum zones (UMZs) separated by thin internal shear layers (ISLs). While the velocity structures have been extensively studied in more specific forms such as momentum streaks, streamwise rolls, and bulges, the shear layers have received less attention outside the context of the hairpin packet paradigm. In the present thesis, the universality of this self-organization is evaluated using a novel field-scale particle image velocimetry (PIV) experiment in the logarithmic region of the atmospheric surface layer. The field measurements are validated using collocated sonic anemometry. The experiment reveals the same organization of UMZs and ISLs occurs for atmospheric flows. The properties of the UMZs and ISLs are then compared using ten PIV experiments and a direct numerical simulation, which together span a wide range of surface roughness and three orders of magnitude in Reynolds number. The UMZs unambiguously scale with the friction velocity and wall-normal distance in the logarithmic region, regardless of Reynolds number and surface roughness. The scaling behavior is in agreement with Prandtl's mixing length theory and Townsend's attached eddy hypothesis. The results show that the hypothetical eddies of the logarithmic law of the wall manifest in the structural organization of the flow. Separate analysis focusing on the smaller structures shows that the ISLs and large vortices are both governed by the friction velocity and Taylor microscale. Preliminary evidence suggests these ISL and vortex scaling behaviors both result from mutual interaction with the local large-scale UMZs, possibly through a stretching mechanism. Additional experiments in three dimensions are required to verify the dynamics. The overall findings support the universality of large-scale structures in the outer region and provide promising clues for better understanding scale interaction and energy transfer mechanisms.
  • Thumbnail Image
    Item
    Particle image velocimetry measurements of smooth- and rough-wall turbulence from the SAFL Atmospheric Boundary Layer wind tunnel
    (2020-01-10) Heisel, Michael; Guala, Michele; mguala@umn.edu; Guala, Michele; St. Anthony Falls Laboratory, University of Minnesota
    Wall-bounded turbulent flows under smooth- and rough-wall surface conditions were measured using particle image velocimetry (PIV) in the Atmospheric Boundary Layer Wind Tunnel at St. Anthony Falls Laboratory (SAFL), University of Minnesota. In the rough-wall case, the tunnel surface was covered with woven wire mesh. The smooth- and rough-wall conditions were each measured for two free-stream velocities (7 m/s and 10 m/s), totaling four flow cases. The friction Reynolds number in the four cases ranges from 3,800 to 14,000. In each case, the PIV imaging field was oriented in the streamwise–wall-normal plane. To enhance the spatial resolution, the measurement field was positioned in the lowest 10 cm of the boundary layer, capturing the roughness sublayer and logarithmic region in the rough-wall cases. Separate high-frequency hotwire anemometer measurements of the full boundary layer profile were used to estimate the scaling parameters such as the boundary layer thickness. This dataset includes the processed velocity vector fields from the PIV measurements and the key scaling parameters.