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<p>Rapidly increasing energy consumption and exhaust emissions are alarming to the environment; hence, improving fuel economy has been the top priority for most automotive manufacturers. The mirror of cars generates drag force as the wake forms at the rear of the side mirror because of its shape. The basic process for the shape development of side view mirrors has evolved into optimizing the design to achieve better aerodynamic characteristics, especially drag reduction. This study applies a gradient-based adjoint optimization framework within ANSYS Fluent to reduce the aerodynamic drag of an isolated side-view mirror geometry. Four candidate mirror designs (ID1–ID4) were evaluated through turbulent CFD simulations using the k-ω Shear Stress Transport (SST) turbulence model. The adjoint solver was configured for incompressible, isothermal RANS-based flow optimization using second-order spatial discretization and Least Squares Cell-Based gradient evaluation. The drag coefficient (C<sub>d</sub>) was selected as the minimization objective, with convergence monitored over 2000 iterations. The CFD methodology was validated using the Ahmed Body at a 25˚ slant angle, yielding a variation of 3.46%. Mirror ID4, exhibiting the lowest baseline C<sub>d</sub> of 0.367 among the four candidate designs, was selected for adjoint-based shape optimization. The optimized geometry achieved a C<sub>d</sub> of 0.320 in CFD analysis, representing a 15.31% reduction relative to the base design. Experimental validation was conducted in a closed-circuit wind tunnel across freestream velocities of 15–30&#xa0;m/s, yielding an 18.25% drag reduction for the optimized mirror (C<sub>d</sub> = 0.303) relative to the experimental base design (C<sub>d</sub> = 0.357), with CFD-to-experimental deviations of 2.7% and 5.3% for the base and optimized designs, respectively. Furthermore, experimental analysis was performed for the base and optimized design and the Toyota Corolla 2005 and Axio 2013 side-view mirrors. The adjoint optimized mirror reduced drag by 15.31% and 18.25% in the CFD and experimental analysis, respectively, compared to the base design which had a drag coefficient of 0.367. Additionally, the optimized mirror reduced drag by 34.16% and 23.15% compared to the Corolla 2005 and Axio 2013 side-view mirrors, respectively. The adjoint-optimized mirror demonstrated a 17.3% reduction in mirror drag-induced fuel consumption compared to the baseline design, indicating a measurable contribution to overall vehicle fuel economy improvement when considered within the context of total aerodynamic drag, leading to higher fuel economy.</p>

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Experimental characterization and adjoint optimization of side-view mirror geometry for aerodynamic drag reduction

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月12日

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  • Md Saifur Rahman,
  • Md Abu Sadman Sakib,
  • Khairun Nasrin Rimi,
  • Md Mahfuzul Hasan,
  • Mazharul Islam,
  • Tariq Mahbub

摘要

Rapidly increasing energy consumption and exhaust emissions are alarming to the environment; hence, improving fuel economy has been the top priority for most automotive manufacturers. The mirror of cars generates drag force as the wake forms at the rear of the side mirror because of its shape. The basic process for the shape development of side view mirrors has evolved into optimizing the design to achieve better aerodynamic characteristics, especially drag reduction. This study applies a gradient-based adjoint optimization framework within ANSYS Fluent to reduce the aerodynamic drag of an isolated side-view mirror geometry. Four candidate mirror designs (ID1–ID4) were evaluated through turbulent CFD simulations using the k-ω Shear Stress Transport (SST) turbulence model. The adjoint solver was configured for incompressible, isothermal RANS-based flow optimization using second-order spatial discretization and Least Squares Cell-Based gradient evaluation. The drag coefficient (Cd) was selected as the minimization objective, with convergence monitored over 2000 iterations. The CFD methodology was validated using the Ahmed Body at a 25˚ slant angle, yielding a variation of 3.46%. Mirror ID4, exhibiting the lowest baseline Cd of 0.367 among the four candidate designs, was selected for adjoint-based shape optimization. The optimized geometry achieved a Cd of 0.320 in CFD analysis, representing a 15.31% reduction relative to the base design. Experimental validation was conducted in a closed-circuit wind tunnel across freestream velocities of 15–30 m/s, yielding an 18.25% drag reduction for the optimized mirror (Cd = 0.303) relative to the experimental base design (Cd = 0.357), with CFD-to-experimental deviations of 2.7% and 5.3% for the base and optimized designs, respectively. Furthermore, experimental analysis was performed for the base and optimized design and the Toyota Corolla 2005 and Axio 2013 side-view mirrors. The adjoint optimized mirror reduced drag by 15.31% and 18.25% in the CFD and experimental analysis, respectively, compared to the base design which had a drag coefficient of 0.367. Additionally, the optimized mirror reduced drag by 34.16% and 23.15% compared to the Corolla 2005 and Axio 2013 side-view mirrors, respectively. The adjoint-optimized mirror demonstrated a 17.3% reduction in mirror drag-induced fuel consumption compared to the baseline design, indicating a measurable contribution to overall vehicle fuel economy improvement when considered within the context of total aerodynamic drag, leading to higher fuel economy.