Unsteady separation and oscillations in a compressible wake of a cylinder
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866913459381207040 |
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| author | Gai, Sudhir Talluru, Krishna Nandhan, Akshay |
| author_facet | Gai, Sudhir Talluru, Krishna Nandhan, Akshay |
| contents | The paper presents a new analysis and a new interpretation of oscillations observed in the experiments of near wakes of cylinders at Mach 4 and Mach 6 and Reynolds number range 2 $\times$ 10$^4$ to 5 $\times$ 10$^5$ by \cite{schmidt2015oscillations} and \cite{thasu2022strouhal}. It is shown that the presence of such oscillations is strongly Reynolds number dependent. It is further shown that there is a threshold Reynolds number below which wake unsteadiness and oscillations do not appear. Attention is drawn to the earlier experimental investigation of supersonic wakes behind cylinders and spheres by \cite{kendall1962exp} which discusses cylinder oscillations and confirms the concept of threshold Reynolds number. Following the earlier work of \cite{goldburg1965strouhal} on hypersonic wakes of spheres and cones, a Strouhal number($St_θ$) based on total wake momentum thickness ($θ$) is shown to be the relevant similarity parameter for correlating the hypersonic and high supersonic wakes of spheres, cones, as well as cylinders. In this limited sense, $St_θ$ can be said to be `universal'. A universal Strouhal number based on only one geometry (\textit{i.e.,} a circular cylinder) and over a limited Reynolds number range as proposed by \cite{schmidt2015oscillations} is much too restrictive. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2408_02933 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Unsteady separation and oscillations in a compressible wake of a cylinder Gai, Sudhir Talluru, Krishna Nandhan, Akshay Fluid Dynamics The paper presents a new analysis and a new interpretation of oscillations observed in the experiments of near wakes of cylinders at Mach 4 and Mach 6 and Reynolds number range 2 $\times$ 10$^4$ to 5 $\times$ 10$^5$ by \cite{schmidt2015oscillations} and \cite{thasu2022strouhal}. It is shown that the presence of such oscillations is strongly Reynolds number dependent. It is further shown that there is a threshold Reynolds number below which wake unsteadiness and oscillations do not appear. Attention is drawn to the earlier experimental investigation of supersonic wakes behind cylinders and spheres by \cite{kendall1962exp} which discusses cylinder oscillations and confirms the concept of threshold Reynolds number. Following the earlier work of \cite{goldburg1965strouhal} on hypersonic wakes of spheres and cones, a Strouhal number($St_θ$) based on total wake momentum thickness ($θ$) is shown to be the relevant similarity parameter for correlating the hypersonic and high supersonic wakes of spheres, cones, as well as cylinders. In this limited sense, $St_θ$ can be said to be `universal'. A universal Strouhal number based on only one geometry (\textit{i.e.,} a circular cylinder) and over a limited Reynolds number range as proposed by \cite{schmidt2015oscillations} is much too restrictive. |
| title | Unsteady separation and oscillations in a compressible wake of a cylinder |
| topic | Fluid Dynamics |
| url | https://arxiv.org/abs/2408.02933 |