V11 N3 eISSN 2477-6041 artikel 11, pp. 395 – 400, 2020 Corresponding Author: syamsuri@itats.ac.id Received on: July 2020 Accepted on: September 2020 395 Syamsuri Lecturer Institut Teknologi Adhi Tama Surabaya Mechanical Engineering syamsuri@itats.ac.id Zain Lillahulhaq Lecturer Institut Teknologi Adhi Tama Surabaya Mechanical Engineering M Yusron Student Institut Teknologi Adhi Tama Surabaya Mechanical Engineering SIMULATION OF FLUID FLOW THROUGH SEDAN CAR YRS 4 DOORS WITH SPEED VARIATION USING CFD Aerodynamic forces that occur around the vehicle must be consid- ered since it involves safety, ergonomic, and fuel consumption. To reduce fuel consumption, the vehicle should be built as aerodynam- ic as possible to minimize drag forces. The vehicle becomes unsta- ble at high speed due to increasing lift force. To balance the vehicle at high speed, a downforce should be generated to keep the tires at- tached to the road surface. Each type of car has a various value of aerodynamic force due to its design, dimension, and cross-section area. The characteristics of streamflow around the car are dis- cussed in this paper. This research simulated 2D sedan car YRS 4 Doors in the steady condition in various velocities, i.e. 23 m/s, 26 m/s, and 40 m/s. This simulation used the Quad Pave mesh model and run in k-ε implicit turbulence model. The characteristics could be observed from the qualitative and quantitative data. The quanti- tative data used as measurable data were Coefficient of Pressure (C P ) and Drag Coefficient (C D ). Quantitative data was shown to outline a better visual explanation of the streaming characteristic. The qualitative data used in this paper are path lines, velocity vec- tors, and contours. The high-velocity stream results in a low value of C P . When the fluid flowed at high speed through a surface, it had low pressure. The coefficient of drag in the high-speed car de- creased as the free stream increased. The value of the coefficient of drag (Cd) from this research was app. 0.567. Keywords: Sedan Car, Drag Coefficient, Quad Pave Mesh Model, CFD 1. INTRODUCTION Fluid which flows around the car is causing drag and lift forces on the vehicle. The lift force has an acceleration effect on the vehicle. This is caused by the lift force on the vehicle reducing the friction which occurs between the vehicle wheels and road. Meanwhile, the drag force causes velocity reduction effect in the vehicle. The magnitude of lift and drag force on the vehicle are determined by several factors, including: flow velocity, cross-sectional area, shape and weight of the car. Drag and lift forces are considered as aerodynamic force. Aerodynamic force that occurs around the vehicle must be considered as well, because it involves safety, ergonomic and fuel consumption. To reduce fuel consumption, the vehicle should be built as aerodynamic as possible to reduce drag [1]. The vehicle becomes unstable at high speed according to the increment of lift force. In order to balance the vehicle in high speed, down force should be generate to keep the tires attach to the road surface [2]. Fluid which flows around the car, pass the upward area of the vehicle and separate to flow along the upper and underneath body. The pressure difference of underneath the car and upper body of the car will cause drag and lift force. The stream from underneath and upper of the vehicle body are flow through to the tail area and create secondary flow [3]. In lower velocity flow, the secondary flow rolls behind the vehicle and create two anti-clockwise vortexes. In higher velocity flow, the vortex behind the vehicle swept by stream which flow under the vehicle and the upper stream flow direct to the ground [4]. Accessories such as spoilers, vortex generators or change tire models can add to improve vehicle stability [5]. Spoiler is able to increases tires capability to produce cornering force, stabilizes vehicles at high