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Effect of an initial boundary layer thickness on the turbulent flow over a backward-facing step

Abstract

The effect of an initial boundary layer thickness on the turbulent flow over a backward-facing step is investigated by using large eddy simulations. Three different initial boundary layer thickness, \(\delta /h\) = 0.26, 0.5, 1.2 and three different Reynolds numbers, \({\text{Re}} =\) 5,100, 24,000 and 45,000 are considered. Expansion ratio is 1.2. The characteristics of the turbulent flow over a backward-facing step (e.g. reattachment length, maximum pressure coefficient, mean streamwise velocity, rms streamwise velocity fluctuations) significantly depends on both the Reynolds number (\({\text{Re}}\)) and the initial boundary layer thickness (\(\delta /h\)) rather than \({\text{Re}}_{\theta }\) or \(\delta /h\) alone as considered in the literature. In addition at high \({\text{Re}}_{\theta }\) the effect of initial boundary layer thickness shows an asymptotic characteristic in terms of \({\text{Re}}_{\theta }\) to some extent. On the other hand, the instability of the detached shear layer based on the momentum thickness (\(St_{\theta }\)) could be reasonably scaled by \({\text{Re}}_{\theta }\). The frequency corresponding to the shedding model varies depending on both \({\text{Re}}\) and \(\delta /h\), which also indicates the fact that the development of the large-scale structures determining the turbulence quantities depends on the two parameters.

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Acknowledgements

This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2017M2A8A4018482). The author would like to express many thanks to Prof. Kang (Sogang University) for providing the code about the backward-facing step.

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Correspondence to Jungwoo Kim.

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Kim, J. Effect of an initial boundary layer thickness on the turbulent flow over a backward-facing step. JMST Adv. 3, 55–62 (2021). https://doi.org/10.1007/s42791-021-00042-y

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  • DOI: https://doi.org/10.1007/s42791-021-00042-y

Keywords

  • Backward facing step
  • Initial boundary layer thickness
  • Shear layer mode