Abstract
We are concerned with the CFD simulation of annular rotor-stator cavities using the general purpose second-order finite volume method (FVM) solver OpenFOAM® and Large Eddy Simulation (LES) methods. Simulations of cavities with smooth surfaces are conducted at various Reynolds numbers, and the properties of the mean turbulent flows are validated against experimental and numerical data available in the literature. Comparisons show that second-order accurate FVM approaches can produce high-fidelity simulations of rotor-stator cavities to an acceptable accuracy and are therefore a viable alternative to the computationally intensive high-order methods. Our validated second-order FVM model is then combined with the parametric force approach of Busse and Sandham [“Parametric forcing approach to rough-wall turbulent channel flow,” J. Fluid Mech. 712, 169–202 (2012)] to simulate cavities with a rough rotor surface. Detailed flow visualisations suggest that roughness-induced disturbances propagate in the downstream direction of the rotor flow toward the outer wall of the cavity. The outer wall subsequently provides a passage to transport said roughness effects from the rough rotor layer to the smooth stator layer. We demonstrate that rotor-stator cavity flows are sensitive to even small roughness levels on the rotor surface alone.
Highlights
The flow inside a rotor-stator cavity is a topic of enduring interest within the scientific community, because of the rich and complicated flow structures found in its boundary layers and owing to its relevance to many engineering applications
The lack of the radial pressure gradient causes a radial outflow within the rotor layer and a radial inflow on the stator layer, but shear layers are observed on the outer sidewall and the inner rotor hub which permit an exchange of fluid between the rotor and stator layers
The instantaneous tangential velocity contours on the stator show the same trend that was observed in the rotor boundary layer: At higher Reynolds number regions, the roughness effects become more intense as the roughness height increases in the rotor boundary
Summary
The flow inside a rotor-stator cavity is a topic of enduring interest within the scientific community, because of the rich and complicated flow structures found in its boundary layers and owing to its relevance to many engineering applications. Makino et al. conducted a similar numerical investigation and, at Reω = 4 × 105, found the rotor boundary layer to feature 16 spiral arms These were suggested to be due to a Type II instability—which is in contrast to the conclusions of Severac et al. So far, all investigations discussed have implicitly assumed smooth surfaces within the rotor-stator cavities, or that the effects of the roughness on the flow field are negligible. The very recent investigation of Ozkan et al. conducted experimental and numerical studies of rotor-stator cavities, paying particular attention to a comparative understanding of roughnessinduced and geometric-induced effects They conclude that the geometric and roughness properties impose similar effects on the flow. Using the parametric force model of Busse and Sandham, on the rotor surface in combination with our second-order accurate FVM LES approach, we investigate the effects of rough wall rotor-stator cavities
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