Using localized wall discharge to control the fluid flow and heat transfer for the flow over a backward facing step

Abstract

Purpose

Studying the effect of localized wall discharge on the fluid flow and heat transfer for a flow over backward facing step is the main purpose of this paper. Jet is used to control the reattachment length which controls the fluid flow and heat transfer downstream the step. Several parameters are to be investigated: geometric; expansion ratio, location of the jet, and jet angle flow; Reynolds number, jet velocity.

Design/methodology/approach

Numerical simulation using both the standard K−ε and renormalized group turbulence theory (RNG) K−ε models are used to model flow in the computational domain. The energy equation is also used to model the heat transfer characteristics of the flow. The model equations are solved numerically using a finite volume code.

Findings

It is found that the presence of the wall jet at a proper location can significantly influence the flow and heat characteristics of the problem. Furthermore, varying the ratio of the jet velocity to the main stream velocity could play an important role in controlling the size of the circulating bubble and, therefore, the fluid and heat transfer characteristics of the flow, whereas, the expansion ratio has less influence. It is also found that increasing Reynolds number increases the value of maximum heat transfer but has less influence on either its location or the reattachment length.

Research limitations/implications

The range of the Reynolds number considered in this research covers only the turbulent regime. The research does not cover laminar flows. The results and conclusions cover only three values of expansion ratios. Namely (expansion ratio (ER)=1.67, 1.8 and 2). Conclusions should not be read beyond these values of ER.

Practical implications

This work gives designers of similar flows a new method of controlling the fluid flow and heat transfer by varying jet angle.

Originality/value

This work has not been done before and it can initiate additional research projects as investigating the effect of applying wall jets in combustors.

Citation

Kiwan, S. (2008), "Using localized wall discharge to control the fluid flow and heat transfer for the flow over a backward facing step", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 18 No. 6, pp. 745-765. https://doi.org/10.1108/09615530810885551