Bi-stable flow in parallel triangular tube arrays with a pitch-to-diameter ratio of 1.375

A study of the bi-stable flow in parallel triangular tube arrays with a pitch to diameter ratio of 1.375 has been performed. Using surface pressure data from two instrumented cylinders (one cylinder with 36 circumferential pressure taps, one cylinder with 27 axial pressure taps) and particle image velocimetry (PIV) data, the bi-stable phenomenon has been investigated. Mode-averaged PIV was performed in a draw down wind tunnel using a 125 mm tube array of 28 clear perspex tubes with a diameter of 13 mm in a Reynolds number range of 0.63-1.27×104. The mode of each set of image pairs was determined by simultaneously capturing the images and gathering pressure data from the surface of the test section wall. Further tests were then conducted using two instrumented cylinders mounted in a larger wind tunnel using 28 tubes with a diameter of 38 mm. The Reynolds number range was 1.84-9.19×104. It was found that at certain flow velocities, the pressure signals from each of the instrumented cylinders were highly correlated. Using this data, the circumferential pressure distributions across the span of an instrumented cylinder were determined for each mode using pseudo modal decomposition (PMD). From this the spanwise fluid forces were determined for each mode.