Correlation based fluidelastic analysis of tube arrays in two-phase flow

In single phase flow, the fluid forces may be considered to be fully correl ated along the tube span. This is not the case for two-phase flow. For tube lengths much longer than the typical linear dimension of the two phase flo w unit structure (slug, bubble etc.), forces along the tube span are only p artially correlated. III this paper, an unsteady Bow model taking into acco unt partial spanwise correlation of the fluid forces is presented. The mode l is applied to fluidelastic instability analysis of a long span heat excha nger tube model. It is shown that the effect of partial correlation is to r educe the effective net fluid forces which thus raises the effective instab ility threshold. Another important result is the introduction of additional coupling between modes that would otherwise be uncoupled in the fully corr elated case. This has important implications for heat exchanger tubes which have closely spaced modes. Lastly, partial correlation is found to elimina te multiple instability boundaries at low values of the mass-damping parame ter; this is a practically significant result.