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Numerical Simulation of Air Flow around the NP Car Using the Realizable k-ε Turbulence Model to Predict Aerodynamic Forces and Moments
M. Siavashi,
Volume 6, Issue 2 (6-2016)
Abstract

In this study, a numerical computational fluid dynamics study is conducted in order to predict the aerodynamic forces on the NP car. The turbulent air flow around the car is modeled using the realizable k-ε model. First, results are validated against those presented for the Ahmed’s body. Next, the fluid flow around the car is simulated for different car speeds ( to mph) and flow directions ( to degree) and the drag and lift forces and coefficients are calculated. Increasing the car speed leads to increase of the drag and lift forces. While, the drag and lift coefficients of the car for all studied speeds are almost constant and are respectively equal to . and . . In addition, for different flow directions the drag coefficient would increase up to . . Also, the effect of mirrors on the drag force is investigated. Results reveal that removing the mirrors leads to approximately reduction in the drag force with no significant reduction in the drag coefficient. Furthermore, the effect of car elevation on the drag and lift forces is analyzed. It has been shown that when the car elevation decreases up to mm, the drag force will decrease more than , and the drag and lift coefficients are still constant. Keywords: road sign detection, text detection, object detection from video, fuzzy logic, MSER


A Numerical Investigation of Inter-Vehicle Spacing on Aerodynamic Drag Using a Two-Dimensional Ahmed Body Model
Ata Ahmadabadi Asle Alamdari, Hamed Chehrmonavari, Amirhasan Kakaee,
Volume 16, Issue 1 (3-2026)
Abstract
This study employs two-dimensional CFD simulations to analyze how rear slant angle and inter-vehicle spacing dictate aerodynamic drag in a tandem Ahmed body configuration. We systematically evaluated slant angles from 15° to 45° and longitudinal spacings from X/L = 0.1 to 0.5. The results delineate three distinct aerodynamic regimes for the trailing vehicle: a drafting zone at close distances (X/L=0.1) with significantly reduced drag, an interference zone (X/L=0.2-0.3) where drag peaks, and an independence zone (X/L>0.4) where vehicles behave aerodynamically isolated. Furthermore, the model successfully captures the critical drag rise as the slant angle surpasses 30°, a key flow transition. While the simulation over-predicts absolute drag values, which is an expected outcome of the 2D approach, it demonstrates high fidelity in capturing complex trends, providing foundational insights for optimizing vehicle platooning strategies.

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