As shown in the figure attached, the turbulent fluid flow around a floating (i.e. partially submerged) cylinder with a rectangular cross-section is to be modelled. Clearly, the forces and torques acting on the cylinder are oscillatory due to the vortex shedding phenomenon. The ultimate goal is to study the cylinder stability on the surface. The question is then how to characterize the fluid forces. Particularly, I have no idea if such a stability analysis could be based on the time-averaged forces or the instantaneous values may play a dominant role. How to characterize and quantify the significance of time-averaged values versus instantaneous values in this specific application?
I would appreciate any comment.
I think that depends also on the specific goal of the study. If you are interested in a case of statistically steady turbulence problem, that is a steady regime of the submerged body, the time-averaged forces could be studied. But if you are interested in the transient or you are interested in specific events, you need to perform a DNS or LES simulation to compute a time-dependent solution. In any case from DNS/LES data you can always produce post-processed time-averaged data. For this reason I would suggest this latter study.
Seniors Ghanem F. Oweis and Steven L. Ceccio was writed: An identification procedure is used to characterize multiple regions of compact vorticity in the flow fields as series of Gaussian vortices. Significant differences are found between the vortex properties from the time-averaged flow fields and the average vortex properties identified in the instantaneous flow fields. Variability in the vortical flow field results from spatial wandering of the vortices, correlated fluctuations of the vortex strength and core size, and both correlated and uncorrelated fluctuations in the relative positions of the vortices. This variability leads to pseudo-turbulent velocity fluctuations. Corrections for some of this variability are performed on the instantaneous flow fields. The resulting processed flow fields reveal a significant increase in flow variability in a region relatively far downstream of the blade trailing edge, a phenomenon that is masked through the process of simple averaging. This increased flow variability is also accompanied by the inception of discrete vortex cavitation bubbles, which is an unexpected result, since the mean flow pressures in the region of inception are much higher than the vapor pressure of the liquid. This suggests that unresolved fine-scale vortex interactions and stretching may be occurring in the region of increased flow variability.
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