Abstract
This paper presents the results of numerical simulations of flow in a periodic channel with the walls covered in the central part by spherical elements that have the same overall surface areas but different radii. Two distributions of the sphere are considered, with the subsequent rows placed one after another or shifted. The computations are performed using the high-order code, whereas the solid elements are modelled with the help of the immersed boundary method. For selected cases, the results are validated by comparison with the solutions obtained using the ANSYS Fluent code on a very dense body-fitted mesh. It was found that the increase in the sphere diameter slows down the flow, which is attributed to the larger blockage of the channel cross-section caused by larger spheres and the occurrence of intense mixing (recirculation) between the spheres. The velocity profiles in the vicinity of the sphere are largely dependent on sphere diameter and rise when it increases. It was found that the distribution of the spheres plays an important role only when the spheres are large. In the part of the channel far from the sphere, the velocity profiles are significantly influenced by the sphere diameter but seem to be independent of the sphere distributions.
Highlights
Flows over rough surfaces occur commonly in nature and the industry
The computations were performed using the high-order code, whereas solid elements were modelled with the help of the immersed boundary method
It was found that the increase of the sphere diameter causes larger overall drag force, which is attributed to the larger blockage of the channel cross-section and the occurrence of the recirculation between the large diameter spheres
Summary
Roughness is often the result of natural processes based on adaptation to environmental conditions (e.g., tree bark or animal skin) or created purposely to improve or control the efficiency of technical devices (e.g., heat exchangers, golf balls, turbine blades, airplanes) In the latter case, the required roughness is usually obtained during the manufacturing process by shaping the walls to obtain waviness or by embedding small solid elements on their surfaces. Hu et al [8], Croce and D’Agaro [9], and Guo et al [10] considered the roughness formed by rectangular, triangular, prismatic elements or peaks distributed randomly or in a predefined manner They found that the topology of these elements, both the type and localization, significantly affects the pressure drop, drag force, and heat transfer. The accuracy of the IB method is confirmed by comparison with the results obtained on a body-fitted mesh
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