A Divide-and-Conquer Machine Learning Approach for Modelling Turbulent Flows

TL;DR

This paper introduces a divide-and-conquer zonal machine learning approach for turbulence modeling in fluid flows, significantly improving prediction accuracy over traditional non-zonal models by partitioning flow domains into physics-based zones.

Contribution

The paper presents a novel zonal ML framework for RANS turbulence modeling, demonstrating enhanced accuracy through domain partitioning and localized model training.

Findings

Zonal models outperform non-zonal models in predicting shear anisotropy.

Zonal approach improves Reynolds stress prediction accuracy by at least 23%.

Partitioning flow into zones enables highly localized optimization of ML models.

Abstract

In this paper, a novel zonal machine learning (ML) approach for Reynolds-averaged Navier-Stokes (RANS) turbulence modelling based on the divide-and-conquer technique is introduced. This approach involves partitioning the flow domain into regions of flow physics called zones, training one ML model in each zone, then validating and testing them on their respective zones. The approach was demonstrated with the tensor basis neural network (TBNN) and another neural net called the turbulent kinetic energy neural network (TKENN). These were used to predict Reynolds stress anisotropy and turbulent kinetic energy respectively in test cases of flow over a solid block, which contain regions of different flow physics including separated flows. The results show that the combined predictions given by the zonal TBNNs and TKENNs were significantly more accurate than their corresponding standard non-zonal models. Most notably, shear anisotropy component in the test cases was predicted at least 20% and 55% more accurately on average by the zonal TBNNs compared to the non-zonal TBNN and RANS, respectively. The Reynolds stress constructed with the zonal predictions was also found to be at least 23% more accurate than those obtained with the non-zonal approach and 30% more accurate than the Reynolds stress predicted by RANS on average. These improvements were attributed to the shape of the zones enabling the zonal models to become highly locally optimized at predicting the output.