Computational Design of Drag Diminishing Active Flow Control Systems for Heavy Vehicles

Abstract

The presented work describes the development of a computationally inexpensive method that has been used for the design and study of Active Flow Control (AFC) systems aimed towards drag reduction for heavy vehicles. The AFC devices chosen are Coanda jets, which have been positioned in all four trailing edges of the fully three-dimensional Ground Transportation System (GTS) model. The jet actuation reduces the wake size and increases the base pressure, reducing the pressure differential on the vehicle and ultimately causing a significant drag reduction. The integrated forces on the vehicle have been computed using Reynolds-Averaged Navier-Stokes (RANS) and the jet configuration changes were quantified using SU2, an open-source Computational Fluid Dynamics (CFD) suite. This study ultimately shows an optimized AFC configuration which reduces drag by 15% and the power used by 12% on a 6.5% scale version of the GTS model. of maintaining flow attached and of increasing the wake pressure 6 relative to cases without jets. These experiments have demonstrated not only drag reduction, resulting in a net power savings of more than 15%, but also an improvement in vehicle stability and safety through the use of flow injection to compensate for the effect of side forces. 4 For the effective design of AFC systems, it is necessary to understand the effects that each part of the system has on the flow features. Due to the complexity of the problem and appearance of separation, Large Eddy Simulation (LES) is believed to be the most reliable method when it comes to the simulation of these flows. Unfortunately, this approach increases the computational requirements significantly, making it prohibitively expensive for use in a design process, given current computational resources. In order to be able to use Computational Fluid Dynamics (CFD) for the design of AFC systems, it is necessary to use a combination of tools that will allow us to simulate the flow around heavy vehicles with an acceptable level of accuracy. In previous studies, 7, 8 the combination of Jameson-Schmidt-Turkel (JST) 9 numerical scheme and the Shear-Stress-Transport (SST) 10 turbulence model have been demonstrated as a good compromise between accuracy and computational cost for design purposes.This article builds upon the previous two-dimensional studies and leverages the knowledge of the flow physics that was gained in order to study the three-dimensional Ground Transportation System (GTS) model. The use of a three-dimensional ground vehicle introduces the stabilizing influence of the ground, 11, 12 which combined with the low frequency flow oscillations found by Khalighi et al. 13 using Unsteady Reynolds-Averaged Navier-Stokes (URANS), justifies the use of Reynolds-Averaged Navier-Stokes (RANS) for the computation of integrated forces in a similar manner as the work presented by Roy et al. 14 and Salari et al.. 15 Furthermore, the lowest drag condition for the two-dimensional GTS model, outfitted with Coanda Jets in the back, is achieved when the wake is confin...

Computations of Active Flow Control for Heavy Vehicle Drag Reduction

“…15 This approach was used by the authors in 2016 and the integrated forced were in good agreement with experimental results. 6 Furthermore, the lowest drag condition for the two-dimensional GTS model, outfitted with Coanda jets in the back, was shown to be achieved when the wake is confined and exhibits a steady behavior. 7,8,16 The introduction of this type of AFC in the GTS model further justifies the use of RANS to investigate the effect that the jet strength has on the aerodynamic drag and power consumption of the vehicle.…”

“…This study is an extension of Manosalvas et al, 6 where a 6.5% scale model was used to study the effect of a Coanda jet based AFC drag reduction system in the aerodynamic profile of the vehicle. The enhanced GTS model, which is the base GTS model outfitted with the Coanda jet drag reduction system in the back, was used and can be seen in Figure 1.…”

“…To recover proper behavior, these boundary conditions were implemented in SU2 [18][19][20] as characteristic-based inlet conditions 21 with both the velocity and density being specified on the jet face. The jet profiles have been modeled in accordance with the authors' 2016 study 6 and for completeness can be seen as Equations 5 and 6 for the two-dimensionally mapped polynomial, and Equations 7, 8, 9, and 10 for the span-wise profile.…”

“…5 These aerodynamic changes can be designed to reduce the pressure imbalance between the front and rear of the vehicle and through this avenue decreasing its drag. 6 Coanda jet-based AFC systems positioned on the back of a heavy vehicle have been tested in wind tunnel experiments, and have proven to be successful at maintaining the flow attached longer. 5 AFC systems have demonstrated not only drag reduction, resulting in a net power savings of more than 15%, but also an improvement in vehicle stability and safety through the use of flow injection to compensate for the effect of side forces.…”

“…In order to be able to use Computational Fluid Dynamics (CFD) for the design of AFC systems, it is necessary to use a combination of tools that will allow us to simulate the flow around heavy vehicles with an acceptable level of accuracy. In previous studies, [6][7][8] the combination of Jameson-Schmidt-Turkel (JST) 9 numerical scheme and the Shear-Stress-Transport (SST) 10 turbulence model have been demonstrated as a good compromise between accuracy and computational cost for design purposes.…”