Three-dimensional structural characteristics of flow separation induced by a forward-facing step in a turbulent channel flow

The near-wall turbulent flow in the rough-wall channel is of great significance in engineering applications, but remains a challenge for both experimental measurement and numerical modeling due to the complexity of the roughness geometry. For optical measurement techniques, e.g. PIV, obstruction by the roughness elements and reflection from the surface adversely affect the quality of near wall data. Our present study utilizes a facility containing a fluid with the same refractive index as the rough acrylic wall, making the interface almost invisible, and employs Stereo PIV to obtain the three-dimensional flow field in the vicinity of the roughness elements. The roughness shape is a uniformly distributed and closely packed, 0.5 mm high pyramid, corresponding to 95 wall units, with a pitch angle of 22.5 degrees. The length of the rough surface is sufficiently long to obtain self-similar roughness boundary layer, turbulent channel flow at a mean velocity of 3.8 m/s, with a clearly defined log layer. Results will include sample data of the complete flow, both around and above the roughness elements. Issues related to implementation of Stereo PIV in an index-matched facility will be discussed.

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Coherent structures in the inner part of a rough-wall channel flow resolved using holographic PIV

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.382 ◽

2012 ◽

Vol 711 ◽

pp. 161-170 ◽

Cited By ~ 20

Author(s):

Siddharth Talapatra ◽

Joseph Katz

Keyword(s):

Channel Flow ◽

Three Dimensional ◽

Streamwise Vortex ◽

Turbulent Channel Flow ◽

Rough Wall ◽

Roughness Sublayer ◽

Reynolds Stresses ◽

Mean Flow ◽

Speed Flow ◽

Spanwise Vorticity

AbstractMicroscopic holographic PIV performed in an optically index-matched facility resolves the three-dimensional flow in the inner part of a turbulent channel flow over a rough wall at Reynolds number ${\mathit{Re}}_{\tau } = 3520$. The roughness consists of uniformly distributed pyramids with normalized height of ${ k}_{s}^{+ } = 1. 5{k}^{+ } = 97$. Distributions of mean flow and Reynolds stresses agree with two-dimensional PIV data except very close to the wall (${\lt }0. 7k$) owing to the higher resolution of holography. Instantaneous realizations reveal that the roughness sublayer is flooded by low-lying spanwise and groove-parallel vortical structures, as well as quasi-streamwise vortices, some quite powerful, that rise at sharp angles. Conditional sampling and linear stochastic estimation (LSE) reveal that the prevalent flow phenomenon in the roughness sublayer consists of interacting U-shaped vortices, conjectured in Hong et al. (J. Fluid Mech., 2012, doi:10.1017/jfm.2012.403). Their low-lying base with primarily spanwise vorticity is located above the pyramid ridgeline, and their inclined quasi-streamwise legs extend between ridgelines. These structures form as spanwise vorticity rolls up in a low-speed region above the pyramid’s forward face, and is stretched axially by the higher-speed flow between ridgelines. Ejection induced by interactions among legs of vortices generated by neighbouring pyramids appears to be the mechanism that lifts the quasi-streamwise vortex legs and aligns them preferentially at angles of $54\textdegree \text{{\ndash}} 63\textdegree $ to the streamwise direction.

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DUGKS simulations of three-dimensional Taylor–Green vortex flow and turbulent channel flow

Computers & Fluids ◽

10.1016/j.compfluid.2017.03.007 ◽

2017 ◽

Vol 155 ◽

pp. 9-21 ◽

Cited By ~ 21

Author(s):

Yuntian Bo ◽

Peng Wang ◽

Zhaoli Guo ◽

Lian-Ping Wang

Keyword(s):

Channel Flow ◽

Vortex Flow ◽

Three Dimensional ◽

Turbulent Channel Flow

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Experimental investigation of the three-dimensional flow structure around a pair of cubes immersed in the inner part of a turbulent channel flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.184 ◽

2021 ◽

Vol 918 ◽

Author(s):

Jian Gao ◽

Karuna Agarwal ◽

Joseph Katz

Keyword(s):

Experimental Investigation ◽

Flow Structure ◽

Channel Flow ◽

Three Dimensional ◽

Turbulent Channel Flow ◽

Three Dimensional Flow ◽

Dimensional Flow

Abstract

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Final stages of transition to turbulence in plane channel flow

Journal of Fluid Mechanics ◽

10.1017/s002211208400241x ◽

1984 ◽

Vol 148 ◽

pp. 413-442 ◽

Cited By ~ 23

Author(s):

S. Biringen

Keyword(s):

Flow Field ◽

Turbulent Flows ◽

Channel Flow ◽

Stokes Equations ◽

Flow Direction ◽

Three Dimensional ◽

Plane Channel ◽

Turbulent Channel Flow ◽

Transition To Turbulence ◽

Plane Channel Flow

This paper involves a numerical simulation of the final stages of transition to turbulence in plane channel flow at a Reynolds number of 1500. Three-dimensional incompressible Navier–Stokes equations are numerically integrated to obtain the time evolution of two- and three-dimensional finite-amplitude disturbances. Computations are performed on the CYBER-203 vector processor for a 32 × 51 × 32 grid. Solutions indicate the existence of structures similar to those observed in the laboratory and characteristic of the various stages of transition that lead to final breakdown. In particular, evidence points to the formation of a A-shaped vortex and the subsequent system of horsehoe vortices inclined to the main flow direction as the primary elements of transition. Details of the resulting flow field after breakdown indicate the evolution of streaklike formations found in turbulent flows. Although the flow field does approach a steady state (turbulent channel flow), the introduction of subgrid-scale terms seems necessary to obtain fully developed turbulence statistics.

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