Analytical and experimental studies of tube/support interactions in multi-span heat exchanger tubes

Steam generators and heat exchangers are essential components of nuclear power stations. Fretting damage of tubes due to tube/support or tube/tube interaction as a result of flow-induced vibrations can have costly consequences. Present analysis techniques can generally avoid vibrations excited by periodic wake shedding and fluid-elastic instability, however low levels of tube vibration will always be present due to random turbulent excitation. This is acceptable as long as data from the successful steam generators and heat exchangers can be applied to new designs. However, as new materials and new geometries for tube supports are being considered to meet new performance requirements, e.g. inhibition of corrosion, information relating to tube vibration and fretting wear is essential. The RMS contact forces at the tube supports have been shown to play a major role in the rate of fretting-wear. This paper presents experimental and computer simulation results for a multi-span tube apparatus vibrating under a variety of conditions. For the first time, experimental measurements of tube/support contact forces are presented for a multi-span tube vibrating in orbital motion. The computer simulations use the VIBIC code in which beam finite elements represent the tube. The modes of vibration are obtained for a tube without intermediate supports and are numerically integrated and superimposed to yield the tube response. The normal and tangential components of the contact force at each support depend upon the tube motion and are generated separately during the simulation. (orig.)