Abstract
ABSTRACT The flow of air past a smooth surface-mounted hemisphere is investigated numerically using six common RANS turbulence models and seeking steady flow solutions. Where possible, the turbulence models are applied using standard wall functions, resolving the viscous sublayer, and the enhanced wall treatment option in ANSYS Fluent. Results of the simulations are compared against measurements taken in a wind tunnel experiment. The comparison shows that enhanced wall treatment and resolving the boundary layer on a low Reynolds number mesh yields superior accuracy compared to standard wall functions or resolving the boundary layer on a high Reynolds number mesh, for all the turbulence models considered. The RNG k - ε model with enhanced wall treatment applied is found to yield the most accurate prediction of the static pressure distribution across the surface of the hemisphere model. Conversely, the Reynolds Stress model and the standard k - ω model are found to give the least accurate predictions, irrespective of the near-wall modelling approach applied. It is found that good agreement with the experimental data for this case offlows can be attained using each of the near-wall modelling techniques if a well-suited turbulence model is used. Keywords: hemisphere, wind tunnel, turbulence modelling, computational fluid dynamics, steady flow
Highlights
Curved structures are prevalent throughout the natural and built environment in the form of domed buildings, fixtures on aircraft and marine vessels, and some species of plants
Comparing figures 6 and 8 shows that the predictions of the kk − εε model and its variants are considerably more accurate when enhanced wall treatment is used. This stands in contrast with the predictions of the Reynolds Stress model and kk − ωω model, in which changing the near-wall modelling approach is found to bring about little improvement
A suitability assessment of different turbulence models was conducted for the case of flow over a smooth surfacemounted hemisphere, comparing the steady flow solutions of numerical simulations performed using six common Reynolds-averaged Navier-Stokes (RANS) turbulence models and a variety of near-wall modelling approaches against experimental data
Summary
Curved structures are prevalent throughout the natural and built environment in the form of domed buildings, fixtures on aircraft and marine vessels, and some species of plants. Existing literature shows that the flow field established around the relatively simplistic geometry of a hemisphere is highly complex, exhibiting features such as formation of vortices at the front and rear of the body, transition from laminar to turbulent flow, and vortex shedding in the turbulent wake [1, 2] These features of the flow can be challenging to capture accurately with numerical modelling techniques, when computational efficiency requirements demand a steady flow solution to be sought. The present work seeks to meet this objective by comparing the results of various numerical simulations in which each of the commonly used RANS turbulence models listed in table 1 are applied - using both standard wall functions and low Reynolds number modelling as appropriate, against experimental data. Sampling of the data received via the data logger was performed using the measurement software VI Logger (Version. 2.0.1 [6])
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