Abstract
LES simulations at Re = 1 × 105 and wind tunnel experiments at Re = 5 × 105 were conducted to investigate the beneficial effect of an active flow control (AFC) technique on the aerodynamic performance of a simplified truck geometry. The paper involves the investigation of a synthetic jet actuator characterized by periodic blowing and suction that defines a zero net mass flux flow control mechanism. The actuation aims to suppress the flow separation occurring at the A-pillar (front rounded corner) of a truck cabin. The work flow is defined as it follows. First, LES at low Reynolds number are conducted for different disposition of the actuation slots. The results show a beneficial effect when the actuation slots are positioned in streamwise direction compared to spanwise (vertical) direction. Second, based on the previous considerations, wind tunnel experiments are conducted to verify and support the numerical findings. Both numerical solutions and experimental data show the same trend and the superiority of the streamwise slots actuation when compared to traditional vertical slot actuation. In particular, this work shows the weakness of a vertical slot actuation, when its location is not optimized. A small change in its positioning greatly worsen the efficacy of the separation control in terms of drag reduction and separation bubble length. The slot location directly affects the length of the separated flow region which its reduction can vary between 40–70% based on the positioning. Conversely, a streamwise actuation, spanning a larger portion of the curvature of a rounded A-pillar, is not affected by this behaviour and contributes up to 80% of the recirculation bubble reduction measured in the unactuated case. The effect of the location change and the orientation of a zero net mass flux jet slot is therefore investigated and discussed in this work.
Highlights
The suppression of separated flow regions around road vehicles is key to reduce their aerodynamic drag and optimize their power consumption
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
In the final part of this section, the findings of the large eddy simulations (LES) investigation are applied to a 3D experimental model, verifying the flow control benefits in terms of aerodynamic performance
Summary
The suppression of separated flow regions around road vehicles is key to reduce their aerodynamic drag and optimize their power consumption. The control of turbulent separated flows is 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. Studies on ground vehicle applications have approached this problem using different techniques, from suction and oscillatory blowing [14,15,16] to plasma actuators [17,18,19] In parallel to these techniques, synthetic jet actuators have shown to be extremely effective, especially for pressure induced separating flows. The main objectives of this paper are listed below:
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