Large-eddy simulation of accelerated turbulent flow in a circular pipe

Abstract

Turbulent pipe flows subject to temporal acceleration have been considered in this study.Large-eddy simulations (LESs) of accelerated turbulent flow in a circular pipe were performed to study the response of the turbulent flow to temporal acceleration. The simulations were started with the fully-developed turbulent pipe flow at an initial Re number, and then a constant temporal acceleration was applied. During the acceleration, the Reynolds number of the pipe flow, based on the pipe diameter and the bulk-mean velocity, increased linearly from Re D = 7000 to 36000. A dimensionless response time for various flow quantities was introduced to measure the delays in the response of the near-wall turbulence to temporal acceleration. The results reveal distinctive features of the delays responsible for turbulence production, energy redistribution, and radial propagation. The conditionally-averaged flow fields associated with Reynolds shear stress producing events were analysed. In the transient flows, sweeps and ejections were closely linked to the delays of turbulence production and of turbulence propagation away from * Corresponding author: Y.M.Chung@warwick.ac.uk the wall. It is found that strong sweep events were related to the delayed turbulence production in the near-wall region, while ejection events were associated with the propagation of the turbulence away from the wall. The results show that the anisotropy of the turbulence was enhanced during the transient, and this would be a challenging problem to standard turbulence models.

The effect of Reynolds number on turbulent drag reduction by streamwise travelling waves

“…The pressure is updated via the Poisson equation, taking advantage of the uniform grid discretisation in the streamwise and spanwise directions by performing a combination of a two dimensional Fourier transform and a tridiagonal matrix inversion. Various versions of the code have been used for DNS and large eddy simulations (LES) (Chung & Talha 2011;Jewkes et al 2011;Jung & Chung 2012;Chung & Hurst 2014).…”

Large-eddy simulations of temporally accelerating turbulent channel flow

“…The mean pressure gradient (P x ) is dynamically adjusted during the simulation to maintain a prescribed mass flow rate. [11] The Reynolds number (Re = U m h/ν) is based on the bulk-mean velocity and the channel half-height.…”

“…The LES results identified the three delays observed in the experiment. However, because of a smaller Reynolds number range used, the response of the flow near the pipe centreline was not clearly captured in Jung and Chung [11]. Seddighi et al [12] also reported a constant acceleration case for a shorter Reynolds number range between Re τ = 180 and 420.…”

“…[7][8][9][10] Recently, a constant acceleration case was studied numerically. Jung and Chung [11] performed large-eddy simulations (LES) of accelerating turbulent pipe flow. The simulation started with an equilibrium turbulent flow at Re D0 = 7000 (or Re τ = 230).…”

“…This Reynolds number range is the same as the one used in the pipe flow experiment of He and Jackson [5]. The Reynolds number range considered in this study is much larger than the range used in previous numerical studies of the transient turbulent channel/pipe flow [7,11,12]. The aim of this study is to investigate the unsteady turbulent flow with the temporal acceleration.…”