CFD Investigation of Flow Over a Backward-facing Step using an RNG k-? Turbulence Model

Abstract

Backward-facing step (BFS) is a benchmarked geometry for visualizing recirculation flow and validating turbulence models. Nowadays, numerical analysis with the CFD method has became more popular and has stimulated research involving CFD without avoiding the experimental method. In this paper, flow over a BFS was numerically investigated with an RNG k-? turbulence model to predict recirculating flow. BFS geometry refers to the geometry proposed by Kasagi & Matsunaga; it is three-dimensional, with inlet Re = 5.540. The paper aims to investigate the performance of the RNG k-? turbulence model over a BFS. Two important parameters were analayzed: the performance of the RNG k-? on the recirculation zone and on the reattachment length. Recirculation flow is presented by the x-velocity for Y = 17.4 mm and Y = 34.9 mm. In these Y-section, the RNG k-? is compared to the STD k-? and both models show the recirculation flow occurred from X = 0 mm to about X = 200 mm. The following results were obtained. The RNG k-? predicted a slightly higher x-velocity component than that predicted by the STD k-?. This result shows that the RNG k-? turbulence model is suitable for predicting recirculation flow on the BFS. The reattachment length was measured by non-dimensional X/h to the x-velocity component with the RNG k-? turbulence model. The analyzed data were taken from X/h = 4.5 to X/h = 10, on the x-velocity component from Y = 17.4 mm. The reattachment point was achieved at X/h = 7.22, close to that achieved by Kasagi & Matsunaga of X/h = 6.51.

Keywords

• Backward-facing step
• CFD
• Reattachment point
• Recirculation flow
• RNG k-? turbulence model