Extreme wall shear stress events in turbulent pipe flows: spatial characteristics of coherent motions

Abstract

Abstract

Transient dynamics of accelerating turbulent pipe flow

“…The present data were collected using the spectral element solver Nek5000 (Fischer, Lottes & Kerkemeier 2019). The numerical schemes used to conduct the current DNS have been explained in detail in Guerrero, Lambert & Chin (2020). In all the cases investigated herein, the simulations ran for at least seven turnovers (TU b /L z ) on a periodic domain with a streamwise length L z = 8πR before the flow was accelerated.…”

“…Herein we validate the transient behaviour of the present DNS data of case TP2 (Re τ ≈ 170-320) with the results from the detailed DNS study of transient channel flow by , which has been conducted at similar Reynolds numbers. Fully-developed resolved turbulent fields from Guerrero et al (2020) have been used as the initial steady-state before the flow excursion. It should also be mentioned that the benchmark data were computed for a different geometry (channel flow), after a step-wise increment in the flow rate, and slightly different initial and final Reynolds numbers (Re τ ≈ 180-420).…”

Precursors of backflow events and their relationship with the near-wall self-sustaining process

“…As vorticity is generated only at the wall, and its spanwise/azimuthal component ω θ is highly associated with the high positive values of the viscous shear at the wall dU x /dy, it would be counterintuitive to consider negative ω θ regions at the wall in canonical wall-bounded flows (Eckelmann 1974). Nevertheless, recent numerical (Örlü & Schlatter 2011;Lenaers et al 2012;Jalalabadi & Sung 2018;Pan & Kwon 2018;Cardesa et al 2019;Guerrero, Lambert & Chin 2020;Wu, Cruickshank & Ghaemi 2020) and experimental (Sheng, Malkiel & Katz 2009;Brücker 2015;Gomit, De Kat & Ganapathisubramani 2018;Willert et al 2018;Bross, Fuchs & Kähler 2019;Tong et al 2020) investigations have revealed that reverse flow events, although rare, actually happen in canonical wall turbulence. Furthermore, reverse flow events have also been studied in adverse pressure gradient TBLs (Vinuesa, Örlü & Schlatter 2017), where these events become more abundant.…”

“…However, it has been shown that some characteristics of BF events such as its lifetime and its size might be universal not only in canonical flows but also in adverse pressure gradient TBL. A near-wall BF event implies the existence of a local region with a negative velocity gradient (dU x /dy < 0) at the wall, which produces small-scale sheets of negative azimuthal vorticity (ω θ < 0) attached to the wall (Guerrero et al 2020). The instantaneous position at which a reverse WSS event occurs (i.e.…”

Análisis del diseño aerodinámico de un alerón preparado para competencia utilizando simulaciones numéricas de dinámica de fluidos computacional (DFC)

“…En el cálculo de la distancia adimensional de la pared corresponde a la distancia de la pared en unidades de longitud, y + es la distancia normal a la pared y el superíndice "+", denota normalización en base a la unidad viscosa (δv = µζ/ν) (Guerrero at al, 2020).…”