Hello Razvan,

for a step channel, most turbulence models should work fine in predicting the main flow parameters, however depending on the various particularities of your case (i.e. Reynolds number, Mach number, heat transfer etc) some might fail at some point. I have seen simulation comparisons with both Ansys (fluent/cfx) and Numeca (fine/turbo) which seem to support that an explicit algebraic reynolds stress model might be the safest choice for these kinds of flows.

Here is an example for a diffuser (which is arguably different than the case you've described but can bear some resemblance) 

ftp://ftp.lfa.mw.tum.de/pub/Software/openfoam/ISABE-2011-1242.pdf

I hope this helps,

Cheers!

Hello

see the papers of Pozarlik et al, this one for example : "HEAT TRANSFER IN A RECIRCULATION ZONE AT

STEADY-STATE AND OSCILLATING CONDITIONS -

THE BACK FACING STEP TEST CASE" 5th European Thermal-Sciences Conference, The Netherlands, 2008 in which three turbulence models are tested

Hello,

i think that the Reynolds stress model might be is the best to modelize this genre of flows, which are characterized by the existence  of the turbulence region..

Harish

Please read this paper to give yrself opportunity to test the various models:

http://files.asme.org/divisions/fed/16311.pdf

Perspective: Selected Benchmarks From Commercial CFD Codes

C. J. Freitas

[+] Author and Article Information

J. Fluids Eng 117(2), 208-218 (Jun 01, 1995) (11 pages)

Good luck and enjoy!

kk

On the principle of independence of the boundary conditions of structure direction of turbulence

Lu Panming

Abstract

This is an introduction to the turbulence modeling theory of the present author, which can take the boundary conditions of turbulence structure into consideration ( the main contents have either not been published in normal journals or only published in chinese papers).   It is included that： (I)。Difficulty Problems Encountered in “Second-Moment-Closure” turbulence modelling ，i.e.  “Gao-Ge Anomaly” ;  (II)。The improvement  to the ”Second-Moment-Closure” turbulence modelling in order to allows the boundary conditions of turbulence structure direction could be prescribed;  (III)。An explanation to the principle of  independence  of  the boundary conditions of

turbulence structure direction ;  (IV)。Six suggestions to the possible future work directions;  (V)。 An explanation to the ”Gao-Ge Anomaly”.

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4. The principle of the independence of the boundary conditions is not only to the turbulence modelling, but also suitable to the other subject, because it is frequently meet the equations are not easy to solve, so there is often a need of modelling or predigestion.  For example, both the D‘Alembert anomaly (~1752) and the Stokes anomaly (~1856), are due to breach the  principle of independence  of the boundary conditions, according to today`s point of view .This is because, first, by using the inviscid potential flow`s dynamic equations it is not possible to affiliate the slip-less condition of the real fluid at the wall, and  second, using the Stokes equation it is not possible to affiliate the boundary conditions both at the wall of cylinder and at the infinite to the cylinder.  The first anomaly lead to the discovery of the Prandlt`s boundary layer theory（1904）, and the  second anomaly  was solved by Oseen（1910）with introducing a modification. All these reflect the scientific worthiness and broad latency of the present principle   of the independence of the boundary conditions.

-----------------

above is an example paragraph,for more details or need the full text, please go to the end of this letter, where will be an  web address existed.

           http://staff.ustc.edu.cn/~pmlu/ 

you can find comparative study for supersonic backward facing step in this article

Assessment of RANS based models in a supersonic flow, 2014

http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4912356

http://staff.ustc.edu.cn/~pmlu/%C2%C0%D6%F8%D5%D5%C6%AC%BB%E3%B1%E0/On%20the%20principle.pdf

read above pdf paper, you may find a new idea  to solve your problem .

I just put the same answer in other forum of research gate. It seems that is an actual field of CFD applications...maybe... Anyway I can tell youy that I did some work related with this topic some years ago. I used the experimental database that you have mentioned for a backward facing step from Driver&Seegmiller (1985). It is a bit older database but quite useful for checking the behavior of turbunece models.These authors have measured mean velocities and its fluctuations, and there is data for the the reattachment length too. I carried out some work related to this topic when I developed my PhD project. You can see this reference (and others), and some turbulence model comparisons in my PhD work. I have uploaded my PhD thesis in Research Gate, and then, I think that you can download it. The name of the work is Theoretical - numerical study of flows with strong streamlines curvature, PhD Thesis ETSEIB, UPC Barcelona Spain.