Fluidelastic instabilities in tube bundles exposed to nonuniform cross-flow

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A mathematical model is presented for fluidelastic instabilities in tube bundles exposed to nonuniform cross-flow, in order to develop an equivalent flow velocity. The model incorporates all motion-dependent fluid forces that are based on unsteady flow theory. Published fluid-force coefficients are compiled and examined; all fluid-force coefficients are approximately independent of the reduced flow velocity when it is high, but are strongly dependent on reduced flow velocity when it is lower. The unsteady flow model is used to show that the mode-weighted averaging method is valid for high reduced flow velocity, but is incorrect at lower reduced flow velocity. In the lower reduced flow velocity range, an iterative procedure is needed to establish the critical flow velocity. The results from the unsteady flow model are compared with those of other mathematical models. A general procedure is recommended for predicting the equivalent flow velocity.