Stream-wise fluidelastic instability has recently been in the spotlight due to a practical event in steam generators at a nuclear power plant . The instability has been reported to occur easily in rotated triangular arrays, but at all hardly in normal triangular arrays . In square arrays, no instability has been reported in the authors’ test facility .
This paper presents the test results on rotated square arrays of the pitch-diameter ratios from 1.2 to 1.5. The tests have been conducted with a wind tunnel, where cylinders have been constrained to move in only one specific direction, either stream-wise or transverse to the flow. The results indicate that fluidelastic vibrations occur only in the stream-wise direction. The critical factor corresponds to the previous data reported in some guidelines , but here the factor is related mainly to stream-wise instability.