Characteristics of Turbulence and Drag Forces on Foreign Objects in Tube Arrays

Abstract

Steam generator tube wear due to foreign objects (FOs) is a significant industry problem. Removal of foreign objects comes with challenges related to accessibility and the environment inside the steam generator. It is therefore of interest to estimate the rate of wear due to foreign objects lodged within the SG; particularly in the tube-sheet region. To estimate wear, the fluid forces acting on the FO are a key input. Much remains unknown regarding the characteristics of fluid forces acting on small objects located within tube arrays. In the work reported here, an exploratory study of fluid forces acting on complex geometry objects was done. Force measurements were conducted in a wind-tunnel on a range of objects to investigate the effect of object geometry on the drag coefficient and the parameters which may be used to develop drag coefficient correlations. Turbulence forces acting on FOs in a tube array were found to be intimately related to turbulence forces acting on the tubes themselves. A direct relation between the corresponding force PSDs, via turbulence force correlations, is reported. This is a potentially useful result with regard to the nature of fluid forces acting on foreign objects in general.