Study on In Flow Fluidelastic Instability of Triangular Tube Arrays Subjected to Air Cross Flow

Abstract

The inflow instability of cylinder arrays corresponds to the inplane instability of Ubend tubes in steam generators. This rarely occurring phenomenon has recently been observed in a nuclear power plant in the U.S. For this reason, the importance of studying this instability has recently increased. The fluidelastic instability of a cylinder array caused by crossflow was found to easily occur in airflow and hardly in waterflow in our previous report. The present report introduces the results of this phenomenon in several patterns of triangular cylinder arrays in airflow. The pitch spacing between cylinders is one of the parameters, which varies from P/D = 1.2 to 1.5, for a fivebyfive cylinder array. The instability is examined both in the inflow direction and in the transverse direction. The test cylinders are supported with thin plates to move in one direction. The number and the location of the flexibly supported cylinders are the other parameters. Differences between the instability in the inflow and in the transverse direction are found. Among these differences the most important is the fact that the fluidelastic instability has not been observed for a single flexible cylinder in the inflow direction, although it is observed in the transverse direction. However, the present preliminary results suggest that the inflow instability may be estimated with the Connors' type formula as likely as in the transverse direction case.