COMPUTATION OF TURBULENT CROSS-FLOW OVER AN IN-LINE TUBE BUNDLE

In this study, we numerically investigate the turbulent cross-flow over an in-line tube bundle consisting of 10 rows of rods arranged with a transverse pitch-to-diameter ratio of 1.5. A three-dimensional incompressible turbulent flow is computed using a large eddy simulation approach at a Reynolds number of 6300 based on the inlet velocity and tube diameter. The validity of the numerical results is first assessed by comparing the time-averaged streamwise velocity distributions behind the tubes and separation points with experimental data. The impact of longitudinal pitch-to-diameter ratio is then analyzed with a discussion of pressure drop and spatio-temporal characteristics of wall pressure fluctuations. INTRODUCTION A turbulent cross-flow over a tube bundle has received much attention in a variety of heat transfer applications. Specifically, it continues to be one of the major concerns in the design of steam generators for nuclear power plants. A great deal of experimental and numerical studies have been conducted in order to clarify the detailed features of the tube bunle flow (Barsamian and Hassan, 1997; Paul et al., 2008) and to predict the pressure drop as well as the heat transfer coefficient (Gaddis and Gnielinski, 1985; Zhukauskas and Ulinskas, 1987). Extensive investigations of velocity and turbulence distributions in the near-wake region have also been made for decades (Balabani et al., 1994; Barsamian and Hassan, 1997; Benhamadouche and Laurence, 2003; Hassan and Barsamian, 2004; Iwaki et al., 2004; Bae et al., 2012). The tube bundle flow is typically characterized by the three-dimensional, unsteady motion of separated shear layers, anisotropic vortices over a wide range of length scales and their interactions, and a high level of turbulence intensity (Hassan and Barsamian, 2004; Iwaki et al., 2004), which are strongly dependent on the tube arrangement and flow condition. These complexities often make numerical simulations of the tube bundle flow a challenging task. For instance, a Reynolds averaged Navier-Stokes (RANS) approach has been widely used for the prediction of turbulent flows in many industrial applications. However, it was reported that RANS models severely underestimate the turbulence level and may not be appropriate for the computation of the tube bundle flow (Paul et al., 2008). On the other hand, large eddy simulation (LES) technique has the potential to provide more accurate predictions of turbulent statistics, and is considered a promising tool for studying the tube bundle flow (Barsamian and Hassan, 1997; Benhamadouche and Laurence, 2003; Hassan and Barsamian, 2004). The primary objective of this study is to investigate the turbulent cross-flow over an in-line tube bundle, with a particular focus on the effect of longitudinal pitch-todiameter ratio. To this end, an incompressible LES is first carried out for a square array of tubes, and the obtained results such as mean velocity profiles behind the tubes and separation angles are compared with experimental data. The influence of tube spacing is then scrutinized in terms of pressure drop and spatio-temporal characteristics of wall pressure fluctuation. COMPUTATIONAL SET-UP Assuming a single-phase incompressible flow of a constant-property Newtonian fluid, the filtered NavierStokes equations read as