Evolution of turbulent pipe flow recovery over a square bar roughness element at a range of Reynolds numbers

Abstract

The Reynolds number effects and scaling on response and recovery of flow over square bar roughness elements are numerically examined at a range of Reynolds numbers between 5 × 103 and 1.56 × 105. The square bar roughness element has a height of 0.05D, where D is the pipe diameter. The response is examined using streamline plots and reattachment lengths. An asymptotic trend is observed in reattachment lengths with increasing the Reynolds number. The recovery is examined quantitatively by tracing the transport of Reynolds shear stress downstream of the roughness element. While the overall trend for recovery is similar for all Reynolds numbers, the collapse of stresses toward the wall appears earlier at lower Reynolds numbers. The recovery trends follow a power-law of diffusion toward the centerline. The point of initial response, that is, the point of collapse, appears independent from the effects of Reynolds numbers at Re ≥ 5.0 × 104.

Response of Viscoelastic Turbulent Pipeflow Past Square Bar Roughness: The Effect on Mean Flow

“…This finding agreed with experiments of Hultmark et al (2012) [51], who recorded similar effects in pipeflow with velocity in the centre of the pipe scaling with increasing Reynolds number. The study of Goswami and Hemmati (2021) [20] showed that the flow response and recovery scaled with changing Reynolds number and observed a reduced mean centerline velocity with increasing the Reynolds number, which was consistent with the observation of the current study. In the case of viscoelastic fluids (Figures 6b and 7b), velocity profiles vastly differed from the trends observed for Newtonian cases.…”

“…The grid spacing for the simulation was ∆x + = 1.85, the Weissenberg number (Wi H ) was 1.82, the polymer extensibility (L 2 ) was 200 and the viscosity ratio, β, was 0.22, consistent with the experiments. The schematics of the axisymmetric computational domain, as shown in Figure 2, was designed following the setup of Smits et al (2019) [16] and Yamagata et al (2014) [46], which was verified by Hemmati (2020, 2021) [19,20] to properly capture the main features of the geometrically-symmetric pipe flow. The axisymmetric perturbation was introduced by placing a square cross section ring with heights of h/D = 0.05 and 0.1 in the pipe.…”

“…It was determined that the flow recovery was prolonged by the use of smaller roughness elements, while the separation patterns had negligible effects on the overall response and recovery as long as the elements are positioned outside the impinging zone of the upstream element. Further, Goswami and Hemmati (2021) [20] investigated the Reynolds number effects and scaling on the response and recovery of the flow over the roughness elements. They considered a square bar roughness element of h/D = 0.05 and Reynolds numbers between 5 × 10 3 and 1.56 × 10 5 .…”

Mechanisms of wake asymmetry and secondary structures behind low aspect-ratio wall-mounted prisms

“…Since the vortex shedding mechanism directly depends on the elongation of the shear layer and spanwise momentum transport (Zdravkovich 2003), we quantitatively analyse the transport and recovery of mean shear layers, under the influence of upwash and downwash flows, in figure 15. Previous studies (Smits, Ding & Van Buren 2019; Goswami & Hemmati 2020, 2021 a ) have used a similar method to investigate the recovery of a separated shear layer downstream of a sudden contraction–expansion system. Figure 15 shows the location of maximum Reynolds shear stress, that is and , in the wake.…”

“…2017) and wakes of trains and trucks (Paul, Johnson & Yates 2009). At low Reynolds numbers, these flow characteristics are commonly seen in mechanisms of electronics and chips(Rastan, Sohankar & Alam 2017), roughness elements in pipes (Goswami & Hemmati 2020, 2021 a , b ) and wall anomalies in the aorta (Jia et al. 2021).…”