An Experimental Study of Fluid-Structure Interaction in Basic In-Line Arrangements of Cylinders

Abstract

Heat exchangers are very common equipment used in numerous industrial facilities all around the world. Throughout the years, engineers have learned how to build them, how to make them more robust and efficient and how to develop and adapt them for a wide variety of applications. Yet the fact remains that the dynamic motion of a flexible cylinder submitted to a cross flow inside a tube bundle responds to physical principles that are still to be fully understood [1]. More specifically, the prediction of whether or not a tube will exhibit damping-controlled instability (flutter) cannot be achieved better than with an acceptable margin of safety, let alone dealing with unknown geometries or conditions of operation. We offer here to go back to the start and to observe this instability experimentally in even simpler geometries under low-turbulent monophasic flow. For this work, we had a small hydraulic loop at our disposal. It lets water flow at Reynolds numbers from 3000 to 10000 through a working section comprising one to three tubes (or a full 4×5 array), among which only one is flexible. A lot of different patterns have been tested, notably cylinders side-to-side along the flow or transverse to it and cylinders in tandem, vibrating either in the lift or in the drag direction. This experimental setup allowed us to plot the tube frequency, its apparent damping and its amplitude according to the reduced velocity. In the end, we aim to provide the community with some supplementary experimental data and hopefully shed some light on the behavior of these oscillating tubes.