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Space-dependent turbulence model aggregation using machine learning

2023-11-14
M. de Zordo-Banliat , G. Dergham , Xavier Merle +1 more
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Space-dependent aggregation of data-driven turbulence models

2023-01-01
Soufiane Cherroud , Xavier Merle , Paola Cinnella +1 more
A machine-learning approach for data-driven Reynolds-Averaged Navier--Stokes (RANS) predictions of turbulent flows including estimates of turbulence modelling uncertainties is developed by combining a Bayesian symbolic identification methodology for learning customised … A machine-learning approach for data-driven Reynolds-Averaged Navier--Stokes (RANS) predictions of turbulent flows including estimates of turbulence modelling uncertainties is developed by combining a Bayesian symbolic identification methodology for learning customised RANS model corrections for selected classes of flows and a space-dependent model-aggregation algorithm that combines the predictions of a set of competing machine-learned RANS models by means of weighting functions depending on a vector of local flow features. The customised model corrections are learned by using the SBL-SpaRTA algorithm, recently proposed by \citet{cherroud2022sparse}, which delivers sparse model correction terms in analytical form and whose parameters are described by probability distribution functions. This makes the learned models naturally interpretable and endowed with a measure of uncertainty. The learned models are subsequently aggregated by training Random Forests Regressors (RFR), which associates a model performance score with a set of local flow features. The scores can be interpreted as the probability that a candidate model performs better than its competitors, given the flow behavior at a given location. Predictions of new flows are then formulated as a locally weighted average of the solutions of a set of machine-learned models. An uncertainty measure is obtained by propagating through the models their posterior parameter distributions and by combining competing model predictions to estimate the inter-model variance. The proposed space-dependent model aggregation procedure (X-MA) is applied to flows of varying complexity, showing significant improvement with respect to the baseline model and good generalizability to unseen flows. The results make X-MA an attractive candidate for the development of a generalizable data-driven turbulence modelling framework with quantified uncertainty.
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Efficient Numerical Method for Global Linear Stability Problem

2007-06-15
Xavier Merle , Jean-Christophe Robinet , A. Lerat

A Domain Decomposition Matrix - Free Method for Global Linear Stability

2010-06-28
Frédéric Alizard , Xavier Merle , Xavier Gloerfelt +1 more

Space-dependent turbulence model aggregation using machine learning

2023-01-01
Maximilien de Zordo-Banliat , G. Dergham , Xavier Merle +1 more
In this article, we propose a data-driven methodology for combining the solutions of a set of competing turbulence models. The individual model predictions are linearly combined for providing an ensemble … In this article, we propose a data-driven methodology for combining the solutions of a set of competing turbulence models. The individual model predictions are linearly combined for providing an ensemble solution accompanied by estimates of predictive uncertainty due to the turbulence model choice. First, for a set of training flow configurations we assign to component models high weights in the regions where they best perform, and vice versa, by introducing a measure of distance between high-fidelity data and individual model predictions. The model weights are then mapped into a space of features, representative of local flow physics, and regressed by a Random Forests (RF) algorithm. The RF regressor is finally employed to infer spatial distributions of the model weights for unseen configurations. Predictions of new cases are constructed as a convex linear combination of the underlying models solutions, while the between model variance provides information about regions of high model uncertainty. The method is demonstrated for a class of flows through the compressor cascade NACA65 V103 at Re~3e5. The results show that the aggregated solution outperforms the accuracy of individual models for the quantity used to inform the RF regressor, and performs well for other quantities well-correlated to the preceding one. The estimated uncertainty intervals are generally consistent with the target high-fidelity data. The present approach then represents a viable methodology for a more objective selection and combination of alternative turbulence models in configurations of interest for engineering practice

Machine-learning-assisted Blending of Data-Driven Turbulence Models

2024-10-18
Mourad Oulghelou , Soufiane Cherroud , Xavier Merle +1 more
A machine learning-based methodology for blending data-driven turbulent closures for the Reynolds-Averaged Navier-Stokes (RANS) equations is proposed to improve the generalizability across different flow scenarios. Data-driven models based on sparse … A machine learning-based methodology for blending data-driven turbulent closures for the Reynolds-Averaged Navier-Stokes (RANS) equations is proposed to improve the generalizability across different flow scenarios. Data-driven models based on sparse Bayesian learning and symbolic regression are pre-trained for specific flow classes, including turbulent channel flows, separated flows, and axisymmetric jets. The specialized models (called "\textit{experts}") are then blended using a set of weighting functions that reflect the local likelihood of a model to capture the reference data. The weighting functions are expressed as functions of a set of local flow features, and Random Forest regressors (RFR) are trained alongside the expert models to learn the mapping between the features and the weights. The training dataset includes additional data for flows ranging from shear flows at equilibrium to separated flows. The resulting blended model is then used to predict unseen flows, including a turbulent zero-pressure-gradient flat plate and a wall-mounted hump involving attached and separated boundary layer regions. The results show that the blending strategy adapts to the local flow conditions and effectively leverages the strengths of individual models, promoting the best-performing models locally, in a manner consistent with the training scenarios. The blended model provides a robust approximation for unseen flows that exhibit similar underlying physical characteristics to the training cases, while also successfully extrapolating to flows with different geometries and physical configurations.
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Machine-learning-assisted Blending of Data-Driven Turbulence Models

2024-10-18
Mourad Oulghelou , Soufiane Cherroud , Xavier Merle +1 more
A machine learning-based methodology for blending data-driven turbulent closures for the Reynolds-Averaged Navier-Stokes (RANS) equations is proposed to improve the generalizability across different flow scenarios. Data-driven models based on sparse … A machine learning-based methodology for blending data-driven turbulent closures for the Reynolds-Averaged Navier-Stokes (RANS) equations is proposed to improve the generalizability across different flow scenarios. Data-driven models based on sparse Bayesian learning and symbolic regression are pre-trained for specific flow classes, including turbulent channel flows, separated flows, and axisymmetric jets. The specialized models (called "\textit{experts}") are then blended using a set of weighting functions that reflect the local likelihood of a model to capture the reference data. The weighting functions are expressed as functions of a set of local flow features, and Random Forest regressors (RFR) are trained alongside the expert models to learn the mapping between the features and the weights. The training dataset includes additional data for flows ranging from shear flows at equilibrium to separated flows. The resulting blended model is then used to predict unseen flows, including a turbulent zero-pressure-gradient flat plate and a wall-mounted hump involving attached and separated boundary layer regions. The results show that the blending strategy adapts to the local flow conditions and effectively leverages the strengths of individual models, promoting the best-performing models locally, in a manner consistent with the training scenarios. The blended model provides a robust approximation for unseen flows that exhibit similar underlying physical characteristics to the training cases, while also successfully extrapolating to flows with different geometries and physical configurations.
View PDF Chat

Space-dependent turbulence model aggregation using machine learning

2023-11-14
M. de Zordo-Banliat , G. Dergham , Xavier Merle +1 more
View PDF Chat

Space-dependent turbulence model aggregation using machine learning

2023-01-01
Maximilien de Zordo-Banliat , G. Dergham , Xavier Merle +1 more
In this article, we propose a data-driven methodology for combining the solutions of a set of competing turbulence models. The individual model predictions are linearly combined for providing an ensemble … In this article, we propose a data-driven methodology for combining the solutions of a set of competing turbulence models. The individual model predictions are linearly combined for providing an ensemble solution accompanied by estimates of predictive uncertainty due to the turbulence model choice. First, for a set of training flow configurations we assign to component models high weights in the regions where they best perform, and vice versa, by introducing a measure of distance between high-fidelity data and individual model predictions. The model weights are then mapped into a space of features, representative of local flow physics, and regressed by a Random Forests (RF) algorithm. The RF regressor is finally employed to infer spatial distributions of the model weights for unseen configurations. Predictions of new cases are constructed as a convex linear combination of the underlying models solutions, while the between model variance provides information about regions of high model uncertainty. The method is demonstrated for a class of flows through the compressor cascade NACA65 V103 at Re~3e5. The results show that the aggregated solution outperforms the accuracy of individual models for the quantity used to inform the RF regressor, and performs well for other quantities well-correlated to the preceding one. The estimated uncertainty intervals are generally consistent with the target high-fidelity data. The present approach then represents a viable methodology for a more objective selection and combination of alternative turbulence models in configurations of interest for engineering practice

Space-dependent aggregation of data-driven turbulence models

2023-01-01
Soufiane Cherroud , Xavier Merle , Paola Cinnella +1 more
A machine-learning approach for data-driven Reynolds-Averaged Navier--Stokes (RANS) predictions of turbulent flows including estimates of turbulence modelling uncertainties is developed by combining a Bayesian symbolic identification methodology for learning customised … A machine-learning approach for data-driven Reynolds-Averaged Navier--Stokes (RANS) predictions of turbulent flows including estimates of turbulence modelling uncertainties is developed by combining a Bayesian symbolic identification methodology for learning customised RANS model corrections for selected classes of flows and a space-dependent model-aggregation algorithm that combines the predictions of a set of competing machine-learned RANS models by means of weighting functions depending on a vector of local flow features. The customised model corrections are learned by using the SBL-SpaRTA algorithm, recently proposed by \citet{cherroud2022sparse}, which delivers sparse model correction terms in analytical form and whose parameters are described by probability distribution functions. This makes the learned models naturally interpretable and endowed with a measure of uncertainty. The learned models are subsequently aggregated by training Random Forests Regressors (RFR), which associates a model performance score with a set of local flow features. The scores can be interpreted as the probability that a candidate model performs better than its competitors, given the flow behavior at a given location. Predictions of new flows are then formulated as a locally weighted average of the solutions of a set of machine-learned models. An uncertainty measure is obtained by propagating through the models their posterior parameter distributions and by combining competing model predictions to estimate the inter-model variance. The proposed space-dependent model aggregation procedure (X-MA) is applied to flows of varying complexity, showing significant improvement with respect to the baseline model and good generalizability to unseen flows. The results make X-MA an attractive candidate for the development of a generalizable data-driven turbulence modelling framework with quantified uncertainty.
View PDF Chat

A Domain Decomposition Matrix - Free Method for Global Linear Stability

2010-06-28
Frédéric Alizard , Xavier Merle , Xavier Gloerfelt +1 more

Efficient Numerical Method for Global Linear Stability Problem

2007-06-15
Xavier Merle , Jean-Christophe Robinet , A. Lerat
Coauthor Papers Together
Paola Cinnella 4
G. Dergham 2
Xavier Gloerfelt 2
Soufiane Cherroud 2
Jean-Christophe Robinet 2
Frédéric Alizard 1
M. de Zordo-Banliat 1
Mourad Oulghelou 1
Maximilien de Zordo-Banliat 1
A. Lerat 1