Streamwise Fluidelastic Instability in Rotated Square Array With Loose Supports

Abstract The potential for fluidelastic instability (FEI), a form of flow-induced vibrations, to cause failure in steam generator tubes has long been recognized. Most research focusing on transverse vibration as the instability critical direction. However, more recent studies and operational incidents, such as the failure of the San Onofre Nuclear Generating Station, have brought attention to the risks due to the possibility of streamwise instability (SFEI), where the instability occurs parallel to the flow direction. This is especially true for U-bend tube bundles with flat-bar supports, where the tubes can vibrate in the inflow direction. In response to the need to better understand these mechanisms and improve operational safety, a research program was initiated at the University of Guelph to study the interaction behavior between tubes and supports in heat exchanger tube arrays. This paper presents an investigation conducted on a rotated square array subjected to single-phase air cross-flow, with pitch ratios ranging from 1.25 to 1.7. Additionally, three different tube/support radial clearance values (0.3, 0.5, and 0.7 mm) were tested to capture the nonlinear dynamic behavior of the loosely supported array. The results were compared with experimental data from existing literature. The findings show that the fluidelastic instability (FEI) threshold is sensitive to the clearance values for the range studied.