Large scale response of a vehicle wake to on-road perturbations

TL;DR

This study investigates how vehicle wakes respond to real-world perturbations using various experimental methods, revealing dominant modes of wake reorganization and emphasizing the importance of low-frequency effects for on-road aerodynamics.

Contribution

It demonstrates that on-road perturbations significantly influence wake dynamics and introduces a quasi-steady approach to evaluate aerodynamic performance and control strategies.

Findings

Two dominant wake modes carry over 50% of energy

Low-frequency energy is higher on-road, affecting wake behavior

Quasi-steady yaw angle analysis replicates on-road phenomena

Abstract

The aim of this research work is to analyse the large scale response of a vehicle wake to on-road perturbations by using an instrumented vehicle and a combination of scale one wind tunnel tests, track trials and on road experiments. More precisely, in all these tests, we focus on the analysis of the asymmetry of the pressure distribution at the base. Proper Orthogonal Decomposition (POD) is used. For all cases considered, POD analysis reveals two dominant modes, respectively associated with vertical and horizontal wake large scale reorganisation. More than 50\% of the total energy is carried by these two modes and this value increases significantly for on-road tests. Noteworthy, the low-frequency energy content of the temporal coefficients of these modes is significantly higher on-road. Low frequencies (even very low ones) then play a major role, corresponding to a quasi-static perturbation domain of the velocity seen by the vehicle. We show that a quasi-steady exploration of the on-road yaw angle statistical distribution during a wind tunnel test captures phenomena similar to those observed on the road and is therefore interesting to evaluate on-road aerodynamic performances. This also opens perspectives for developing closed loop control strategies aiming to maintain a prescribed wake balance in order to reduce drag experienced on the road.