Estimating the Reattachment Length by Realizing a Comparison between URANS k-Omega SST and LES WALE Models on a Symmetric Geometry

Daniel Teso-Fz-Betoño,Unai Fernandez-Gamiz,Martin Juica,Ekaitz Zulueta,Koldo Portal-Porras

doi:10.3390/sym13091555

Daniel Teso-Fz-Betoño, Unai Fernandez-Gamiz + Show 3 more

Open Access

https://doi.org/10.3390/sym13091555

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Journal: Symmetry	Publication Date: Aug 24, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: University of the Basque Country

Abstract

In this study, a water reattachment length was calculated by adopting two different models. The first was based on Unsteady Reynolds-Averaged Navier–Stokes (URANS) k-omega with Shear Stress Transport (SST); the second was a Large Eddy Simulation (LES) with Wall-Adapting Local Eddy-Viscosity (WALE). Both models used the same mesh and were checked with Taylor length-scale analysis. After the analysis, the mesh had 11,040,000 hexahedral cells. The geometry was a symmetrical expansion–contraction tube with a 4.28 expansion ratio that created mechanical energy losses, which were taken into account. Moreover, the reattachment length was estimated by analyzing the speed values; the change of speed value from negative to positive was used as the criterion to recognize the reattachment point.

Highlights

Particle Image Velocimetry (PIV) is a conventional method of visualizing optical flow [1]
This study concluded that the Large Eddy Simulation (LES) Wall-Adapting Local Eddy-Viscosity (WALE) had more speed variance than the Reynolds-Averaged Navier–Stokes (RANS) model
The reattachment point could be settled in the Xr LES ≈ 0.18 m position for the LES WALE and the XrSST ≈ 0.19 m position for the k-omega Stress Transport (SST)

Summary

Introduction

Particle Image Velocimetry (PIV) is a conventional method of visualizing optical flow [1]. It consists of obtaining instantaneous velocity measurements and related properties in fluids that have to be illuminated so that the particles can be seen. A similar method known as Particle Tracking Velocimetry (PTV) determines the velocity of particles in a moving fluid [3]. The difference is that PIV analyzes the mean displacement of small particles, whereas PTV tracks the motion of individual particles. The details obtained from the PTV are the characterization of the particle size, such as the mean particle diameter (in pixels and mm), standard deviation, and the total number of particles detected [4]

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