Exploring Viable Methods of Evaluating and Computing Vehicular Drag and Rolling Friction Force Coefficients by Applying Principles of Geometric Similitude

Author(s): Sanwar A. Sunny

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Abstract: The current study focuses on simple methods of quantifying vehicular drag and rolling resistance coefficients. It highlights the relationship between the drag coefficients (CD) of two models of varying scales but sharing geometric and dynamic similitude and also describe a simple, small scale and low cost, yet comprehensive approach to quantifying the automotive coefficient of Rolling Resistance or Friction (Crr), also known as the Rolling Resistance Coefficient (or RRC). Applying principles of fluid mechanics, especially Bernoulli's law and by scaling models using Reynold's Number (Re) and the Buckingham Pi Theorem at varying velocities u0, drag forces, the drag forces FD were supplementedby conducting simple wind tunnel tests. Real drag analysis show a 10% deviation from the literature data, contributed to negligence of the governing flow equations of Navier Stokes, such as modeling principles relative to turbulence. Some computational flow modeling principles were briefly discussed. For rolling friction coefficient method, coast down and dynamic speed trap tests of scaled models were conducted under varying body weighted conditions to converge on the value, where a high speed camera monitored the motion of the vehicle. The experiment produced different equations of motion which were then solved analytically by numerical analysis techniques to compute the rolling friction coefficient. Initial guesses in the least square optimization iterations provided coefficient values where drag forces were normalized (Crr of 0.0116). Studies were compared with literature and direct scaling abilities were attributed for quantifying the normalized value.