Assessment of CFD capability for prediction of the Coand\u{a} effect

TL;DR

This study evaluates the effectiveness of various CFD methods, including RANS and LES, in predicting the Coande1 effect, highlighting their strengths and limitations in capturing flow attachment and vortices.

Contribution

It systematically compares RANS, curvature correction, 3D RANS, and LES approaches for modeling the Coande1 effect, revealing their capabilities and shortcomings.

Findings

RANS with $k-a$ SST predicts flow attachment well on flat surfaces.

Curvature correction slightly improves jet development predictions.

LES shows potential but was limited by computational resources.

Abstract

The tendency of a jet to stay attached to a flat or convex surface is called the Coand\u{a} effect and has many potential technical applications. The aim of this thesis is to assess how well Computational Fluid Dynamics can capture it. A Reynolds-Averaged Navier-Stokes approach with a 2-dimensional domain was first used to simulate an offset jet on a flat plane. Whether it was for $k-\omega$ SST or $k-\epsilon$ turbulence model, a good prediction of the flow was found. Since it is known that streamline curvature can have an important impact on the numerical results, a jet blown tangentially to a cylinder was then considered. Using the same approach as for the flat plane, with $k-\omega$ SST turbulence model, some of the flow features such as the separation location or velocity profiles near the jet exit were accurately predicted. However, the jet development was overall poorly captured. A Curvature Correction was then introduced in the turbulence model and if it did slightly improve the jet development, the negative impact on other quantities makes its benefits questionable. Due to the known presence of longitudinal and spanwise vortices in the flow, a Reynolds-Averaged Navier-Stokes approach with a 3-dimensional domain was attempted but was only able to reproduce the 2-dimensional results. Although if the longitudinal vortices are artificially generated at the inlet, their development is supported by the simulation. Finally, since the shortcomings of the numerical results obtained might be due to limitations of the Reynolds-Averaged Navier-Stokes approach, a Large Eddy Simulation was attempted. Unfortunately, due to time and computational restrictions a fully developed flow could not be obtained, the methodology and preliminary results are however presented.