Abstract
Turbulent flows around bluff bodies are present in a large number of aeronautical, civil, mechanical, naval and oceanic engineering problems and still need comprehension. This paper provides a detailed investigation of turbulent boundary layer flows past a bluff body. The flows are disturbed by superficial roughness effect, one of the most influencing parameters present in engineering applications. A roughness model, recently developed by the authors, is here employed in order to capture the main features of these complex flows. Starting from subcritical Reynolds number simulations (Re = 1.0 × 105), typical phenomena found on critical and supercritical flow regimes are successfully captured, like non-zero lift force and its direction change, drag crisis followed by a gradual increase on this force, and separation and stagnation points displacement. The main contribution of this paper is to present a wide discussion related with the temporal history of aerodynamic loads of a single rough circular cylinder capturing the occurrence of asymmetric separation bubbles generation. The formation of asymmetric separation bubbles is an intrinsic phenomenon of the physical problem, which is successfully reported by our work. Unfortunately, there is a lack of numerical results available in the literature discussing the problem, which has also motivated the present paper. Previous study of our research group has only discussed the drag crisis, without to investigate its gradual increase and the change on lift force direction. Our results again confirm that the Lagrangian vortex method in association with Large-Eddy Simulation (LES) theory enables the development of two-dimensional roughness models.
Highlights
The technologic and science enhancement in many fields of knowledge is because of deep analysis and consequent comprehension of flow fundamentals around bodies of arbitrary shape
That chosen number for the panels ensures the convergence for the potential solution of the problem and, as consequence, a refined discretization for the vorticity field, which is reflected on the aerodynamic loads computation
This paper describes vortex method with both roughness models atotwo-dimensional capture changes in aLagrangian bluff body aerodynamics
Summary
The technologic and science enhancement in many fields of knowledge is because of deep analysis and consequent comprehension of flow fundamentals around bodies of arbitrary shape. The importance of knowing and mastering this subject can be recognized when it is observed that, most of bodies present in situations of practical interest for engineering, are exposed to air or water flows These flows are typical examples of fluid-structure interaction problems, where the transition to turbulence is undeniably a complex phenomenon of nonlinear hydrodynamics. In Achenbach [3], the surface roughness effect is experimentally studied on the flow past a circular cylinder He used a high-pressure wind tunnel, where high Reynolds number flows up to Re = 3 × 106 could be obtained. The results confirm that two-dimensional Lagrangian vortex method with both LES and roughness models is able to capture the drag crisis, and the non-zero lift force, which is typical of critical Reynolds number flows, and the gradual increase on drag coefficient, which is a typical feature of supercritical flows. A wide range of two-dimensional studies can be found in literature e.g., [14,17,18,25,26,27,28,29,30,31] which includes relevant contributions of our research group
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