Fig. 01, wake behind a stationary cylinder at Re = 190

In order to map the hydrodynamic properties of the flexible structures undergoing complex motions, we relay on the construction of the comprehensive hydrodynamic databases using rigid body experiments with parametric inputs. These experiments can be useful to understand physics of the problem as well as to build a reduced-order model for real-life prediction with an adequate fidelity. 

Taking advantage of the autonomy of the ITT sequential and adaptive experimental capability, I constructed several world-first hydrodynamic databases of the rigid cylinder with a combined-inline-and-crossflow motion, adding additional effects of Reynolds number, wake interference of upstream cylinder and different cylinder configurations. 

01. Reynolds Effect on Rigid Cylinder Forced Vibration (Paper 01)

Various experiments on the rigid cylinder free vibrations [1-3] demonstrated that the Reynolds number play an important role in determining the maximum cross-flow (CF) amplitude response in the CF-only vibration, shown in Fig. 02 (a). Meanwhile, the result of a few experiments on the combined-IL-and-CF rigid cylinder vibration show that the Reynolds number does not affect maximum CF amplitude at least in the subcritical Reynolds number regime, shown in Fig. 02 (b). Unfortunately due to the large number of experiment, no forced vibration data has been collected.

The ITT use active learning to study this problem. The result of the CF-only vibration is shown in Fig. 03, and the result of the combined-IL-and-CF vibration is shown in Fig. 04.

 

Fig. 02, Reynolds number effect on maximum CF amplitude of the rigid cylinder CF-only (a) and combined-IL-and-CF (b) vibration.

CF-Only (Re = 1,200 - 19,000):

Combined-IL-and-CF (Re = 1,200 - 14,000):

Fig. 03, Cd (a), Clv(b) and Cmy (c) for the cylinder forced CF-only vibration from Re = 1,200 to Re = 19,000.

Fig. 04, Clv at given AxD and AyD for the combined-IL-and-CF cylinder forced  vibration for various Re number from 1,200 to 14,000.

02. Rigid Cylinder in the Wake of the Upstream Cylinder (Paper 02)

The existence of the upstream cylinder will greatly alter the hydrodynamic forces on the downstream cylinder, due to the wake interference [4]. 

We conducted the rigid cylinder forced vibration experiment and constructed the first hydrodynamic database for a rigid cylinder forced vibrating in the wake of an upstream cylinder, shown in Fig 06. The result will help to improve the prediction accuracy of the risers in a bundle. 

 

Fig. 05, experimental sketch of a rigid cylinder forced to vibrate in the wake of an upstream cylinder with the same diameter.

Fig. 06, Clv of a rigid cylinder forced to vibrate in the wake of an upstream cylinder with different distance.

03. Multiple Cylinder in the Oscillatory Flow (Paper 03, Paper 04)

Fig. 07, cylinder models used in the experiment.

Compared to the problem of cylinders in the uniform flow, cylinders in the oscillatory flow is less studied.

 

Therefore, we experimentally and numerically studied two identical circular cylinders oscillating in the still water with either a side-by-side (SbS) or a tandem configuration for a wide range of Keulegan-Carpenter (KC) number and Stokes number.

Interesting results, such as the drag enhancement for SbS cylinders and oscillating lift reduction for tandem cylinder at smaller gaps are reported and shown in the Fig. 08 to Fig. 11.

Side-by-side:

Fig. 08, Cd of the two side-by-side cylinders

Fig. 09, wake of the two side-by-side cylinders at KC = 4 (first row) and KC = 8 (second row)

Tandem:

Fig. 10, Clrms of the two tandem cylinders

Fig. 11, wake of the two tandem cylinders at KC = 4 (first row) and KC = 8 (second row)

[1] R. N. Govardhan, C. H. K. Williamson, Defining the ‘modified Griffin plot’ in vortex-induced vibration: revealing the effect of Reynolds number using controlled damping. J. Fluid. Mech. 561, 147-180 (2006).

[2] Bearman, P. W. "Circular cylinder wakes and vortex-induced vibrations." Journal of Fluids and Structures 27.5-6 (2011): 648-658.

[3] Dahl, J. M., et al. "Dual resonance in vortex-induced vibrations at subcritical and supercritical Reynolds numbers." Journal of Fluid Mechanics 643 (2010): 395-424.

[4] Assi, Gustavo Roque da Silva, et al. "The role of wake stiffness on the wake-induced vibration of the downstream cylinder of a tandem pair." Journal of Fluid Mechanics 718 (2013): 210-245.

 
 
 
 

© 2019 by Dixia Fan, a "lazy" fluid mechanist