1 |
Tomographic Measurements of Turbulent Flow through a ContractionMugundhan, Vivek 08 1900 (has links)
We investigate experimentally the turbulent flow through a two-dimensional contraction. Using a water tunnel with an active grid we generate turbulence at Taylor microscale Reynolds number Reλ ~ 250 which is advected through a 2.5:1 contraction. Volumetric and time-resolved Tomo-PIV and Shake-The-Box velocity measurements are used to characterize the evolution of coherent vortical structures at three streamwise locations upstream of, and within the contraction. We confirm the conceptual picture of coherent large-scale vortices being stretched and aligned with the mean rate of strain. This alignment of the vortices with the tunnel centerline is stronger compared to the alignment of vorticity with the large-scale strain observed in numerical simulations of homogeneous turbulence. We judge this by the peak probability magnitudes of these alignments. This result is robust and independent of the grid-rotation protocols. On the other hand, while the point-wise vorticity vector also, to a lesser extent, aligns with the mean strain, it principally remains aligned with the intermediate eigen-vector of the local instantaneous strain-rate tensor, as is known in other turbulent flows. These results persist when the distance from the grid to the entrance of the contraction is doubled, showing that modest transverse inhomogeneities do not significantly affect these vortical-orientation results.
|
2 |
EXPERIMENTAL STUDIES ON FREE JET OF MATCH ROCKETS AND UNSTEADY FLOW OF HOUSEFLIESAngel David Lozano Galarza (10757814) 01 June 2021 (has links)
<p>The
aerodynamics of insect flight is not well understood despite it has been
extensively investigated with various techniques and methods. Its complexities
mainly have two folds: complex flow behavior and intricate wing morphology. The
complex flow behavior in insect flight are resulted from flow unsteadiness and
three-dimensional effects. However, most of the experimental studies on insect
flight were performed with 2D flow measurement techniques whereas the 3D flow
measurement techniques are still under developing. Even with the most advanced
3D flow measurement techniques, it is still impossible to measure the flow
field closed to the wings and body. On the other hand, the intricate wing
morphology complicates the experimental studies with mechanical flapping wings
and make mechanical models difficult to mimic the flapping wing motion of
insects. Therefore, to understand the authentic flow phenomena and associated
aerodynamics of insect flight, it is inevitable to study the actual flying
insects. </p>
<p>In
this thesis, a recently introduced technique of schlieren photography is first
tested on free jet of match rockets with a physics based optical flow method to
explore its potential of flow quantification of unsteady flow. Then the
schlieren photography and optical flow method are adapted to tethered and feely
flying houseflies to investigate the complex wake flow and structures. In the
end, a particle tracking velocimetry system: Shake the Box system, is utilized
to resolve the complex wake flow on a tethered house fly and to acquire some
preliminary 3D flow field data</p>
|
Page generated in 0.0296 seconds