The Effect of Longitudinal Pressure Gradient on Heat Transfer in a Separated Flow Behind a Sudden Expansion of the Channel

Abstract

The results of an experimental study of the influence of longitudinal positive and negative pressure gradients in a rectangular flat channel with a backward-facing step on turbulent heat transfer in the zones of separation, attachment, and relaxation of the flow are presented. The studies were carried out in a turbulent flow regime at Reynolds numbers 4 × 10^3–1.2 × 10⁴. The height of the step was equal to the half height of the channel before separation, so that the degree of its expansion was 1.5. The angle of diffuser opening varied from 0° to 4°, and confuser contraction ranged from 0° to 7.5°. The pressure fields and heat transfer coefficients in the recirculation and relaxation regions of the flow behind a sudden expansion of the channel were measured as a part of the experimental study. It is shown that with a change in the longitudinal pressure gradient, the behavior of the separated flow behind the step changes significantly. It has been determined that for a convergent channel with an increase in the pressure gradient, the maximum value of the Nusselt number increases, while for the expanding channel it decreases. The maximum Nusselt number position shifts downstream with diffuser expansion and approaches a step in the confusion flow.

Additional information

Funding

The work was financially supported by the Russian Science Foundation [project 18-19-00161].

Notes on contributors

Viktor Terekhov

Viktor I. Terekhov is a doctor of technical sciences, professor, researcher of turbulent aerodynamics and heat and mass transfer in complex flow conditions. After graduating from the Moscow Higher Technical School named after N.E. Bauman, all his scientific activity is associated with the Kutateladze Institute of Thermophysics SB RAS. He obtained priority results on heat transfer on permeable surfaces, in flows with phase and chemical transitions, as well as in vortex and separation flows. Most of his research is occupied with investigations of heat transfer enhancement, both in single-phase and multiphase systems. An important place in his work is the creation of engineering methods for calculating the flow characteristics and heat and mass transfer in power equipment.

Aleksey Dyachenko

Aleksey Yu. Dyachenko is a senior researcher of Kutateladze Institute of Thermophysics SB RAS. He has a Ph.D. in Mechanical Engineering from Novosibirsk State Technical University, 2007. His research is aimed at studying the influence of separated flows on heat transfer.

Yaroslav Smulsky

Yaroslav J. Smulsky is leading engineer of Institute of Kutateladze Institute of Thermophysics SB RAS. Currently, his research interests are related to the study of dynamics and heat transfer behind a backward-facing step.