Test of RANS turbulence models for application on ribbed duct flows by comparison to experimental flow field and heat transfer data

Abstract

The aim of the study is to find the most accurate and robust CFD solution that can be applied to cases with flow separation and heat transfer induced by ribs.

The first part of the paper analyses the ability of six Reynolds-Averaged Navier Stokes (RANS) models to reproduce the separated air flow (isothermal) in a transversally ribbed rectangular channel, in comparison to flow field data measured with Laser Doppler Anemometry.

In the next step the models were evaluated in the prediction of convective heat transfer and pressure drop in v-ribbed heated gas cooling channel measured in HETREX-PT (HEat TRansfer Enhancement eXperiments - Pressure, Temperature) experiments at KIT, with a channel geometry close to the intended application.

Turbulence models such as standard k-ω SST (SST) and Realisable k-ε model (KE-RE) as well as models derived on the basis of the elliptic blending approach: Reynolds Stress model (RSM), v2-f model (V2F), Elliptic Blending model (KE-EB) and Lag-Elliptic Blending model (KE-LAG-EB) were selected.

The flow conditions (flow rate, heating power) were scaled from helium flow in HCPB (P=8MPa Tin=300 °C) to air at 0.4 MPa and 24 °C by the two similarity quantities Reynolds number and the dimensionless heating rate q⁺. The rib-arrays consist of upstream pointing transversally oriented 60° V-shaped ribs. The comparative analysis of the turbulence models deals with the investigation of the distribution of vortex structures caused by ribs and their influence on heat transfer.

The flow between attached ribs calculated by k-ω SST is almost completely detached, leading to a significant under-prediction of heat transfer. The standard k-ε model underestimates the turbulence production at the leading edge and in the shear layer over the recirculation region and, thus, the heat transfer between the ribs. The elliptical blending models give results that are closer to the measurements. The RSM, V2F and KE-EB models perform better agreements with experimental data. The V2F model provides the best prediction and is found to be most suitable for the simulation of heat transfer in the presented rib-structured channel flow.