In-Situ Measurement of Wall Effect on The Hydrodynamic Force for a Solid Sphere in Constant Approach at Low Reynolds Number
Date Issued
2012
Date
2012
Author(s)
Lee, Jung-Hua
Abstract
Abstract
This thesis investigates the hydrodynamic forces of an immersed sphere in axis-symmetric approach to a downstream wall via systematic experiments. Sphere motion at constant velocity was generated by precision servo motor to cover a range of particle Reynolds number, 0.5 to 6.8, by changing sphere velocity and liquid viscosity. We attempted synchronized in-situ measurements of the resulting total dynamic force and its dynamic pressure components by integrating conventional load cells and pressure transducers. Pressure measurements were conducted at 0º, 45º, and 90º from the front stagnation point. In addition to the fluid force on the moving sphere, we also attempted a non-intrusive measurement to monitor the strength of the interstitial film motion near wall induced by the approaching sphere.
For both the total force and the pressure components, the data obtained far away from the wall were employed to scale the near-wall data to determine the wall influences. The measured factor for quasi-steady total drag is known as the wall correction factor was found to agree qualitatively with a few model predictions at low Reynolds. For all the examined Re, the wall correction factors for total hydrodynamic force falls on the same trend that increases monotonically with diminished interstitial gap. Such near-wall amplification with dropping gap is also observed for the pressure at front stagnation point and at θ=45º from the approach line. However, the front stagnation point shows an amplification that seems to grow with Re and at a trend much higher than the wall correction factor. The pressure at θ=45º shows much milder rise and only takes place at very small gaps; contrastingly, the pressure at θ=90º remains a comparably small value without any detectable dependence on interstitial gap. At the same time, the squeezed film motion seems to increase with the sphere motion and hence Re, as expected.
Keywords: in-situ measurement of total hydrodynamic force, Stokes drag, wall amplification function, load cell, pressure transducer, strain gauge
Subjects
in-situ measurement of total hydrodynamic force
Stokes drag
wall amplication function
load cell
pressure tranducer
strain gauge
Type
thesis
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