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This paper presents analyses of the effect of blowing flow control and variations on front geometry towards the reduction of aerodynamic drag on vehicle models. Blowing flow control is an alternative measure in modifying the onset of flow separation in the boundary layer on the surface of the vehicle. The modification is expected to reduce the dominating influence of the separation area on the total drag. Conducted in computational and experimental approaches, the research investigated the effect of frontal slant angle variations (θ) of 25°, 30° and 35° towards the reduction of aerodynamic drag on vehicle models on the application of blowing flow control with upstream and blowing speed of 16.7 m/s and 0.5 m/s, respectively. Load cells were used in the experimental method to validate the reduction of aerodynamic drag obtained from computational method. It is indicated that the effects of blowing flow control and variations on front geometry are significant in the increasing on pressure coefficients and the reduction of aerodynamic drag on vehicle models. The largest increase on pressure coefficients of 38.93% is indicated on the vehicle model with θ=35°, while the largest reduction of aerodynamic drag occurred on the same model with the values of 14.81 and 12.54 for computational and experimental methods, respectively.

Drag aerodinamika pada kendaraan disebabkan adanya tekanan rendah dan separasi aliran di bagian belakang, yang berdampak pada menurunnya kecepatan, meningkatnya penggunaan bahan bakar, dan turunnya efisiensi kendaraan. Blowing merupakan salah satu pilihan rekayasa kendali aktif aliran yang dapat diterapkan pada desain kendaraan yang dapat mengendalikan pembentukan separasi aliran dan berefek positif berupa pengurangan hambatan aerodinamis. Penelitian ini bertujuan menganalisis pengaruh penerapan blowing terhadap pola aliran, distribusi tekanan, dan hambatan aerodinamika yang bekerja pada bagian belakang model. Dengan bantuan CFD Fluent 6.3, model uji yang digunakan adalah model kendaraan dengan sudut kemiringan geometri depan (α) 35o dan rasio terhadap model Ahmed bodi original adalah 0.17 (1:6), yang dilengkapi dengan blowing dengan kecepatan 1.0 m/s. Hasil komputasi mengindikasikan bahwa penerapan blowing dapat mengurangi pembentukan wake dan menunda separasi aliran dan dapat meningkatkan koefisien tekanan minimum pada bagian belakang model kendaraan sebesar 24.690%. Pengurangan hambatan aerodinamika diperoleh sebesar 9.583%.

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A boundary element method (BEM) is utilized to find numerical solutions to boundary value problems of quadratically graded media governed by a spatially varying coefficients anisotropic-diffusion convection-reaction (DCR) equation. The variable coefficients equation is firstly transformed into a constant coefficients equation for which a boundary integral equation can be formulated. A BEM is then derived from the boundary integral equation. Some problems are considered. A FORTRAN script is developed for the computation of the solutions. The numerical solutions verify the validity of the analysis used to derive the boundary element method with accurate and consistent solutions. The computation shows that the BEM procedure elapses very efficient time in producing the solutions. In addition, results obtained for the considered examples show the effect of anisotropy and inhomogeneity of the media on the solutions. An example of a layered material is presented as an illustration of the application.

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