Start-up flow past a circular cylinder: A comparison between DPIV and DNS

Abstract

There have been a considerable number of theoretical, experimental and computational studies on vortex shedding. Experimental investigations of unsteady flow behind a starting circular cylinder date back to the Prandtl era [1]. The most extensive experiments to date for an impulsively started cylinder are those presented by Bouard and Coutanceau [2]. At the same time, considerable effort has been directed toward finding both analytical and accurate finite-difference solutions. This previous work provided extensive information about the main flow characteristics but was limited in several respects: all the known analytical solutions are only valid for short times; finite-difference methods often suffer from numerical stability and dissipation problems; and experimental data is limited in both spatial and temporal resolution. The recent development of techniques for measuring instantaneous fields of vectors with high spatial and temporal resolution, such as PIV [3] and its digital counterpart DPIV [4], was an important achievement for modern experimental fluid mechanics. Furthermore, spectral domain decomposition methods have been developed that provide better accuracy and take full advantage of parallel supercomputers for high-resolution calculations. In this paper, complementary advanced experimental and numerical techniques are used to obtain information on secondary flow quantities such as the vorticity, quantities that are crucial in understanding the dynamics of coherent structures. The present study deals with the determination of the plane viscous flow around a circular cylinder that accelerates linearly from rest to a constant speed U_0 in a quiescent fluid. We define the Reynolds number as Re ≡ U_0d/ν, where d is the cylinder diameter and ν is the kinematic viscosity of the fluid. In the results presented here, Re ≈ 1000 and the acceleration time is t* ≡ tU_0/d = 1.575. The objective of this coordinated experimental-computational study is to compare experimental techniques (DPIV) and numerical simulations (DNS) for the start-up flow past a circular cylinder. We chose this problem because its initial features are two-dimensional and it exhibits behavior characteristic of bluff body wake dynamics. The purpose of this ongoing research is to try to shed some light on the fundamental mechanisms governing the vortex formation process by monitoring the evolution of the flow field.

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