Modelling of subcritical free-surface flow over an inclined backward-facing step in a water channel

Jaromír Příhoda,Pavel Zubík,Jan Šulc,Milan Sedlář

doi:10.1051/epjconf/20122502023

Abstract

The contribution deals with the experimental and numerical modelling of subcritical turbulent flow in an open channel with an inclined backward-facing step. The step with the inclination angle α = 20° was placed in the water channel of the cross-section 200×200 mm. Experiments were carried out by means of the PIV and LDA measuring techniques. Numerical simulations were executed by means of the commercial software ANSYS CFX 12.0. Numerical results obtained for twoequation models and EARSM turbulence model completed by transport equations for turbulent energy and specific dissipation rate were compared with experimental data. The modelling was concentrated particularly on the development of the flow separation and on the corresponding changes of free surface.

Highlights

Flow over an inclined backward-facing step in closed channel is an intermediate step from flow in a one-sided diffuser to the flow over a backward-facing step with an abrupt change of the cross-section and with flow separation on the step edge
For flow in open channels with an inclined step, the gravitational forces play in important role and the flow character is quite different for sub- and supercritical flow
The length of the separation region behind the inclined step is approximately xs/H | 7.2, while the length predicted by the EARSM model is xs/H | 7.6

Summary

INTRODUCTION

Flow over an inclined backward-facing step in closed channel is an intermediate step from flow in a one-sided diffuser to the flow over a backward-facing step with an abrupt change of the cross-section and with flow separation on the step edge. The flow pattern is relatively complicated in spite of a simple geometry because of it includes an extensive separation region and secondary flows near side walls behind the inclined step. For flow in open channels with an inclined step, the gravitational forces play in important role and the flow character is quite different for sub- and supercritical flow. The subcritical flow is characterized by a relatively massive separation but only small changes of free surface. Results of the investigation of turbulent flow over an inclined step in the closed channel and in the open channel with sub- and supercritical flow are summarized by Zubík at al.

EXPERIMENTAL ARRANGEMENT

MATHEMATICAL MODEL

RESULTS

CONCLUSIONS