Firm structure of the separated turbulent shear layer behind modified backward‐facing step geometries

Abstract

Purpose

One major challenge in turbulent flow applications is to control the recirculation zone behind the backward‐facing step (BFS). One simple idea to do so is to modify the original BFS geometry, of course, without causing adverse or undesirable impacts on the original characteristics of the primary stream. The main objective of this work is to examine the solidity of the recirculation zone behind several different geometries which are slightly to moderately different from the original BFS geometry.

Design/methodology/approach

The implemented modifications cause complicated irregularities at the boundaries of the domain. The experience shows that the mesh distribution around these irregularities plays a critical role in the accuracy of the numerical solutions. To achieve the most accurate solutions with the least computational efforts, we use a robust hybrid strategy to distribute the computational grids in the domain. Additionally, a suitable numerical algorithm capable of handling hybrid grid topologies is properly extended to analyze the flow field. The current fully implicit method utilizes a physical pressure‐based upwinding scheme capable of working on hybrid mesh.

Findings

The extended algorithm is very robust and obtains very accurate solutions for the complex flow fields despite utilizing very coarse grid resolutions. Additionally, different proposed geometries revealed very similar separated regions behind the step and performed minor differences in the location of the reattachment points.

Research limitations/implications

The current study is fulfilled two‐dimensionally. However, the measurements in testing regular BFS problems have shown that the separated shear layer behind the step is not affected by 3D influences provided that the width of channel is sufficiently wide. A similar conclusion is anticipated here.

Practical implications

The problem occurs in the pipe and channel expansions, combustion chambers, flow over flying objects with abrupt contraction on their external surfaces, etc.

Originality/value

A novel pressure‐based upwinding strategy is properly employed to solve flow on multiblocked hybrid grid topologies. This strategy takes into account the physics associated with all the transports in the flow field. To study the impact of shape improvement, several modified BFS configurations were suggested and examined. These configurations need only little additional manufacturing cost to be fabricated.

Citation

Darbandi, M., Taeibi‐Rahni, M. and Reza Naderi, A. (2006), "Firm structure of the separated turbulent shear layer behind modified backward‐facing step geometries", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 16 No. 7, pp. 803-826. https://doi.org/10.1108/09615530610683520