Microscopic Turbulence Topology Analysis of the Cross Flow Over a Square Arranged Tube Bundle Using Direct Numerical Simulation

Abstract Helical tube bundles with small tube pitches are usually preferable for intermediate heat exchangers (IHXs) of High Temperature Gas-cooled Reactors (HTGRs) for its compactness. Too small tube pitches would introduce more complicated flow features in cross flow over tube bundles. In the current investigation, microscopic analysis on turbulence topology of cross flow over a square arranged tube bundle are investigated using Direct Numerical Simulation (DNS). The time averaged flow field as well as the Reynolds stress distributions are first discussed. Then, a method that utilizes a red-green-blue (RGB) color map to depict the anisotropic states of Reynolds stress are used to analyze the overview Reynolds stress state of cross flow over tube bundles. Traditional Lumley triangle is also used to further investigate detailed Reynolds stress state variation in the near wall region with different pressure gradient and the shear layer. In the region with favorable pressure gradient (FPG), the Reynolds stress state changes from a two-component state near the wall towards a disk-like state (state with two equal components), and eventually reaches an isotropic state in the fully turbulent region. In the region with adverse pressure gradient (APG), the Reynolds stress state changes from a two-component state near the wall towards a rod-like state (one component), and eventually reaches an isotropic state. The Reynolds stress state also appears strong anisotropy (rod-like state) in the shear layer. However, according to one-dimensional energy spectra, the anisotropy near the wall occurs at all wavenumber ranges (all scale ranges), while the anisotropy at the shear layer only occurs at the low wavenumber range (large-scale range).