Large Eddy Simulations of Fully-Developed Turbulent Flows Over Additively Manufactured Rough Surfaces

TL;DR

This study uses high-fidelity LES to analyze turbulent flow over additively manufactured rough surfaces, revealing how surface topography influences turbulence and developing models for better simulation of AM-roughened heat exchangers.

Contribution

It provides a novel LES database for AM rough surfaces and introduces a mixed scaling approach to improve turbulence modeling over such surfaces.

Findings

Logarithmic layer persists even at high roughness levels.

Turbulence strongly depends on surface topography.

Effective wall-normal distance collapses turbulence profiles.

Abstract

In the last decade, progresses in additive manufacturing (AM) have paved the way for optimized heat exchangers, whose disruptive design will depend on predictive numerical simulations. Typical AM rough surfaces show limited resemblance to the artificially constructed rough surfaces that have been the basis of most prior fundamental research on turbulent flow over rough walls. Therefore, a high-fidelity LES database is built to develop and assess novel wall models for AM. This article investigates the flow in rough pipes built from the surfaces created using AM techniques at Siemens based on Nickel Alloy IN939 material. We developed a code to generate the desired rough pipes from scanned planar surfaces and performed high-fidelity LES of turbulent rough pipe flows at Re = 11,700 to reveal the influence of roughness on turbulence, mainly the average roughness height and the Effective Slope. The equivalent sand-grain roughnesses, ks, of the present AM rough surfaces are predicted using the Colebrook correlation. In the present study, the existence of a logarithmic layer is marked even for high values of ks. The mean flow, the velocity fluctuations, and the Reynolds stresses show turbulence's strong dependence on the roughness topography. Profiles of turbulence statistics are compared by introducing an effective wall-normal distance. The effective distance collapses the shear stresses and the velocity fluctuations outside the roughness sublayer; thus, Townsend's similarity of the streamwise mean velocity is marked for the present roughnesses. Furthermore, a mixed scaling is introduced to improve the collapse of turbulence statistics in the roughness sublayer.