DOI: 10.18245/ijaet.1901680 ISSN: 2146-9067

Generic ground vehicle with variable underbody diffuser: suppressing side leakage

Oğuz Baş, Sinan Keyinci
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The Ahmed body is one of the most widely used generic models in automotive aerodynamics. Rear underbody diffusers are known to improve aerodynamic performance by enhancing pressure recovery. However, detailed flow analysis indicates that localized low-pressure regions and lateral vortex structures can limit the effectiveness of a fixed diffuser configuration. In this study, the flow behavior of a 35° Ahmed body equipped with an optimized underbody diffuser is investigated numerically. The analysis focuses on the detailed wake topology and pressure evolution along the diffuser surface to better understand the governing flow mechanisms. Flow visualizations show that side leakage and vortex cores developing near the lateral edges intrude into the diffuser channel and disturb the intended expansion process. To address this limitation, a variable-angle diffuser configuration is proposed and parametrically evaluated. The geometry is adjusted to control the lateral vortex interaction and stabilize the underbody expansion. The variable diffuser reduces side leakage intensity and improves wake alignment. Compared to the fixed diffuser configuration, an additional drag reduction of 51 drag counts is achieved. The results highlight that diffuser performance depends not only on the expansion angle but also on its interaction with lateral flow patterns developing near the underbody and wake regions.

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