Water tunnel experiments were conducted on an equilateral triangular array of tubes with a pitch ratio of 1.5. Eight tests were run with different array orientations so that the effects of incident flow direction on crossflow induced vibrations could be studied. Small amplitude vorticity response was observed for all orientations except the parallel triangular array. A Strouhal number of 0.57 based on pitch velocity and independent of incident flow directions was found. The fluidelastic threshold for the normal triangular array was found to be about twice that of the parallel triangular array. However, the stability threshold for the normal triangular array was found to be quite sensitive to incident flow direction suggesting that advantage of this higher threshold should not be taken in the design of heat exchangers.

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