The balance between compactness and forecast accuracy of data-driven latent-space reduced-order models in controlled wake flows
2026-07-27 • Machine Learning
Machine Learning
AI summaryⓘ
The authors studied methods to create simplified models that predict fluid flow behind objects when controlled by inputs. They compared traditional linear methods (POD) to more complex neural network-based encoders for compressing flow data. While neural networks gave more detailed short-term results, their long-term predictions were less stable and more prone to errors. In contrast, linear methods produced smoother, more reliable forecasts over longer times useful for control decisions. The authors highlight a trade-off between how compact the model is and how stable its predictions are, which is important for real-time flow control applications.
Reduced-Order Models (ROMs)Proper Orthogonal Decomposition (POD)Convolutional Autoencoders (CAEs)Variational AutoencodersLong Short-Term Memory (LSTM)Latent spaceFluid dynamicsWake flowModel predictive controlReinforcement learning
Authors
Alberto Solera-Rico, Patricia García-Caspueñas, Carlos Sanmiguel Vila, Stefano Discetti
Abstract
Model-based active flow control requires predictive models that are accurate, stable, and fast enough for real-time optimisation. In controlled wake flows, this is often achieved through Reduced-Order Models (ROMs) that first compress high-dimensional velocity snapshots into a latent space and then learn a time- stepping predictor for the dynamics in the latent space. Here, we study how the choice of the spatial encoder affects the predictability of the resulting latent coordinates for wake flows under control inputs. Using two actuated 2D wake configurations, a simplified truck wake and the fluidic pinball, we compare Proper Orthogonal Decomposition (POD) against nonlinear Convolutional Autoencoders (CAEs) and two types of variational autoencoders for compression, and evaluate several temporal predictors based on Long Short-Term Memory networks. CAEs achieve higher compression efficiency and sharper short-term reconstructions, but they produce latent dynamics that are more irregular and with broadband spectral content. As a consequence, long-horizon forecasts degrade faster and show a higher probability of catastrophic divergence than POD-based models. POD yields smoother latent trajectories that are easier to learn and extrapolate, leading to more reliable predictions beyond the short- term regime. These results reveal a clear trade-off between compactness and forecast accuracy, and suggest that the stability of the latent dynamics prediction can outweigh maximal compression. This is particularly relevant for control strategies rooted in forecasts of the dynamics, such as model predictive control and reinforcement learning. The findings provide practical guidance for designing actuation-aware, hardware-feasible predictive ROMs for real-time flow control.