Simulation of Flow Control Devices in Support of Vehicle Drag Reduction 2018-01-0713

Flow control devices can enable vehicle drag reduction through the mitigation of separation and by modifying local and global flow features. Passive vortex generators (VG) are an example of a flow control device that can be designed to re-energize weakly-attached boundary layers to prevent or minimize separation regions that can increase drag. Accurate numerical simulation of such devices and their impact on the vehicle aerodynamics is an important step towards enabling automated drag reduction and shape optimization for a wide range of vehicle concepts. This work demonstrates the use of an open-source computational-fluid dynamics (CFD) framework to enable an accurate and robust evaluation of passive vortex generators in support of vehicle drag reduction. Specifically, the backlight separation of the Ahmed body with a 25° slant is used to evaluate different turbulence models including variants of the RANS, DES, and LES formulations. The experimental measurements from Pujals et al. [1] are used for validation and further details such as the total vehicle drag and the slant flow are examined. The adopted simulation framework is demonstrated to accurately capture the flow features of the vortex generators that reduce the backlite separation of the simplified vehicle geometry. The experimental maximum drag reduction of approximately 10% is replicated with both the DES and LES turbulence models. The computational effort and the numerical resolution requirements necessary to simulate the flow control devices are discussed in detail.