The suppression of separated flow regions around road vehicles is key to reduce their aerodynamic drag and optimize their power consumption. In fact, more than 60% of the total power generated by a road vehicle is needed to overcome drag at cruise condition. The aerodynamic drag of a truck is in fact dominated by pressure drag due to heavily separated flow (90% of the total aerodynamic drag) and only a small percentage is attributed to the skin friction resistance [
1]. Many are the regions of separated flow around a heavy duty vehicle (e.g. the gap between tractor and trailer, the wheel housing and the under body or the rear side) and all these areas contribute to an aerodynamic drag increase and to the creation of noise and soiling on the side windows [
1]. Concerning trucks, a multitude of techniques have been developed during the years, from passive [
2,
3] to active [
4‐
8] flow control strategies. Specifically, this work focuses on an active flow control (AFC) strategy to suppress the pressure induced flow separation that appears at the vertical front rounded corners of a truck cabin, generally called A-pillars. The control of turbulent separated flows is in fact one of the highly important topics in fluid mechanics [
9] and the ultimate goal of this ongoing project is to implement an effective AFC able to minimize the side recirculation bubble of a truck cabin. This kind of separation resembles the separated flow around a stalled aerofoil characterized by an early stage shear layer defined by small fluid structures, and a downstream wake mainly composed by large eddies. Previous works of similar aerodynamic conditions have shown the effectiveness of a flow control device, for both static stalled [
10,
11] and pitching [
12,
13] aerofoils. Taking inspiration from the flow control techniques developed in this field, an AFC strategy is investigated and readapted here for ground vehicles. Studies on ground vehicle applications have approached this problem using different techniques, from suction and oscillatory blowing [
14‐
16] to plasma actuators [
17‐
19]. In parallel to these techniques, synthetic jet actuators have shown to be extremely effective, especially for pressure induced separating flows. This work, in particular, aims to follow up the previously published large eddy simulations (LES) [
20] and experimental [
7] works. In these two studies, an AFC was implemented both numerically and experimentally. Following the same path, the implementation of a more robust synthetic jet is studied further by intervening on one specific design variable: the AFC slot disposition along the A-pillar. Without any doubt, flow control based on synthetic jet actuation has a large potential but it is also very dependent on many variables involved. Principally, these variables are the magnitude and frequency of the actuation, the direction of the jet flow and the distribution and the location of the actuation slots. The focus of this paper is on the latter. The main goal is to find and alternative disposition of the actuation slot, for a more robust flow control, that it is not affected by the change of the separation location due to external conditions. Taking inspiration from the work of Vernet [
19], the authors want to show an alternative slot disposition, independent from the location of the flow separation. First, the location of a standard vertical slot actuation is moved in different positions to reproduce the possibility of a flow separation happening after, before or very close to the actuation. Secondly, the effectiveness of an alternative to the vertical actuation slot (a streamwise distribute slot array) is tested. The problem is tackled by using both CFD and wind tunnel experiments. The first approach consists of LES of a simplified geometry. This study is preliminary done to verify the potential of different slot dispositions. Gathering the information from this first section, an experimental campaign is carried out on a fully three-dimensional geometry. In conclusion, the main objectives of this paper are listed below:
The positioning and distributions of the actuation slots has found to play a major role in the control of a pressure induced separation.
A streamwise slot actuation is compared with three vertical slot actuations.
An explanation of the flow mechanism describing the streamwise slot actuation is proposed.
An experimental proof of concept, that corroborates the numerical findings, is also presented here.
The reminder of the article is organized as follows: Section
2 details the numerical and experimental set-up and the corresponding geometrical models. Section
3 is divided in two main parts: first, LES results are presented and a description of the flow control mechanism is proposed. Second, the wind tunnel data (forces measurements, particle image velocimetry (PIV) and tufts flow visualizations) are reported and discussed. Conclusions are presented in Section
4.