Reducing base drag on road vehicles using pulsed jets optimized by hybrid genetic algorithms

TL;DR

This study demonstrates that hybrid genetic algorithms can optimize pulsed jet actuation to significantly reduce aerodynamic drag on bluff bodies like trucks, achieving nearly 9% drag reduction while considering energy costs.

Contribution

It introduces a hybrid genetic algorithm approach for optimizing active flow control in vehicle aerodynamics, effectively reducing drag with energy-efficient strategies.

Findings

Achieved approximately 8.8% drag reduction.

Identified a control law targeting vortex shedding.

Demonstrated model-free optimization effectiveness.

Abstract

Aerodynamic drag on flat-backed vehicles like vans and trucks is dominated by a low-pressure wake, whose control is critical for reducing fuel consumption. This paper presents an experimental study at $Re_W\approx 78,300$ on active flow control using four pulsed jets at the rear edges of a bluff body model. A hybrid genetic algorithm, combining a global search with a local gradient-based optimizer, was used to determine the best-performing jet actuation parameters in an experiment-in-the-loop setup. The cost function was designed to achieve a net energy saving by simultaneously minimizing aerodynamic drag and penalizing the actuation's energy consumption. The optimization campaign successfully identified a control strategy that yields a drag reduction of approximately 8.8%. The best-performing control law features a strong, low-frequency actuation from the bottom jet, which targets the main vortex shedding, while the top and lateral jets address higher-frequency, less energetic phenomena. Particle Image Velocimetry analysis reveals a significant upward shift and stabilization of the wake, leading to substantial pressure recovery on the model's lower base. Ultimately, this work demonstrates that a model-free optimization approach can successfully identify non-intuitive, multi-faceted actuation strategies that yield significant and energetically efficient drag reduction.