The turbulent wake flow past a sphere at ReD= 3700 is investigated via Direct Numerical Simulation (DNS). The characteristic motions in the wake flow, such as vortex shedding and bubble pumping are identified by the probes placed in the near wake with a dominating frequency of St= fuâ/D= 0.22 and 0.004, respectively. The modal analysis is conducted in the wake area using Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The vortex shedding and bubble pumping motions are also captured by the modal analysis. The results from POD and DMD show comparable patterns of both characteristic motions. For the bubble pumping motion, the dominating frequency of the corresponding POD mode is St= 0.004, while the DMD mode that is directly related to the separation bubble has the frequency of St= 0.009.
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This content will become publicly available on September 1, 2025
Flow topology changes with bubbly flow around a circular cylinder
Vortex induced vibration (VIV) experienced during flow past a cylinder can reduce equipment performance
and in some cases lead to failure. Previous studies have shown that the injection of bubbles in the flow
over a cylinder typically leads to a monotonic increase in shedding frequency with void fraction, however, a
satisfactory explanation for this phenomenon has not been proposed. Unexplained scatter in the data exists,
including that the increase in shedding frequency is not universal. More research is needed to characterize
the influence of bubbles on the wake structure, and subsequent shift in shedding frequency. To this aim,
the effect of bubbles on the structure of the wake and VIV was examined over two values of Reynolds
number, đ
đđ· = 100, 000 and 160,000. Time-resolved particle image velocimetry (TR-PIV), proper orthogonal
decomposition (POD) and spectral proper orthogonal decomposition (SPOD) of the wake structures, vibration
of the cylinder, and bubble image velocimetry (BIV) were used to assess the flow topology changes under the
influence of gas injection. Using SPOD/POD analysis in the near wake, it was found that the primary Karman
shedding frequency decreased with the injection of gas, from a Strouhal number of St = 0.2 to St = 0.17â0.18;
the width of the spectral peak was found to increase with void fraction. Notably, the vibration of the cylinder
at the primary Karman shedding frequency was suppressed following the injection of gas, even at spanwiseaveraged volumetric qualities below 0.01%. This suppression occurred regardless of if gas was concentrated locally near the centerline of the channel, or along the span. BIV data suggests that gas accumulation in the near wake, driven by the high velocity vertical motion of gas, serves to uncouple the cylinder motion from the formation of the vortex street downstream while promoting faster wake recovery.
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- Award ID(s):
- 2024672
- PAR ID:
- 10552706
- Publisher / Repository:
- International Journal of Multiphase Flow
- Date Published:
- Journal Name:
- International Journal of Multiphase Flow
- Volume:
- 179
- Issue:
- C
- ISSN:
- 0301-9322
- Page Range / eLocation ID:
- 104917
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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