IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 _______________________________________________________________________________________ Volume: 05 Issue: 04 | Apr-2016, Available @ http://www.ijret.org 16 INVESTIGATING THE DRAG COEFFICIENT OF SCALED MODEL CAR BY USING WIND TUNNEL Sumit Krishnan 1 , Murtaza Ma 2 , Vishal Kesari 3 1 Assistant Professor, Amity University (Lucknow Campus) India 2 Professor, Amity University (Lucknow Campus) India , 3 Assistant Professor, Institute of Engineering and Technology Lucknow UP India Abstract This paper reviews use of scale modelling in automobile performance evaluation. A scale model has been used to experimentally evaluate the automobile aerodynamics in a wind tunnel. Three cases have been considered, they are model without polish, model with polish and model with add-on, a load on the roof. Drag coefficients in all the cases have been computed and compared. Empirical relations can be used to predict drag coefficients on other than test speeds. Keywords: Scale Model, Automobile Aerodynamics, Drag Coefficient, Wind Tunnel, Car, Add-On --------------------------------------------------------------------***---------------------------------------------------------------------- 1. INTRODUCTION A fuel efficient vehicle is needed to conserve fuel and reduce environmental pollution. Fuel efficient means less wastage of power that is efficient power pack and less power consumption in air-conditioning and navigation system. In operation of an automobile, major portion of engine‟s power is wasted in overcoming rolling resistance and aerodynamic drag. The aerodynamic drag exceeds fifty percent of the total resistance to motion at speeds above 70 Km/h. It is the most important factor, responsible for resistance to motion, for speeds above 100 Km/h. Automobile body designers have understood its importance and a large number of efforts have been made [1, 2, 3]. They have tried to stream line vehicle body and use drag reduction add-on devices also. These efforts include studies based on scale modelling and computer simulation approaches. A scale model [4] is most generally a physical representation of an object, which maintains all important aspects, for example material properties so that the interaction with outside world is reliable. Only then these studies will help in improving the performance. Scale models have been used in the study and design of automobiles for aerodynamic drag and interior noise. 2. LITERATURE REVIEW Krylov et al (5) used reduced-scale simplified models of road vehicles for research into vehicle interior noise to predict structure-borne interior noise in real vehicles. Choudhry et al (7) used a 1/10th scale model of a semi- trailer truck and studied the aerodynamic impact of various fuel saving devices used in a commercial vehicle. Drag reduction up to 26% is possible by full-skirting (using the front fairing, side skirting and gap filling) of the tractor and the semi-trailer unit. Sultika and Nozick (8) used a scaled (1:15) model of semi- trailer unit to optimise the design. Rear-end tapering resulted reduction in base-drag. Alam et al (9) used a 25% Scale Model of an Australian passenger car . Vehicle add-ons can generate 5 to 30% more aerodynamic drag depending on yaw angles. It also deteriorates the vehicle directional stability and safety of the vehicle. Rohatgi et al (10) used a small scale model (length 1710 mm) of General Motor SUV t and tested in the wind tunnel. Drag reduction of 26% and 6.5% was obtained by rear fairing and rear screen respectively. Vortex generators were also tested. Aesthetics and practical considerations can effect implementation of these options. 3. PRESENT WORK In the present work, a wooden scale model (length 390 mm) of a popular passenger car „Honda City‟ was used (Figure 1). Wind tunnel of Amity University (Lucknow Campus) UP India (Figure 2 ) was used for these studies. Effect of add-on and surface finish on aerodynamic drag was analyzed. Measurements included manometer readings and drag force. Air velocity was calculated from pressure drop. Figure 1: Scale car model (length 390 mm)