INCAS BULLETIN, Volume 8, Issue 2/ 2016, pp. 15 – 24 ISSN 2066 – 8201 Analyze of aerodynamic forces acting on the Siemens Desiro railcar Sorin ARSENE* ,1 , Ioan SEBESAN 1 *Corresponding author 1 “POLITEHNICA” University of Bucharest, Transport Faculty Depart Rolling Stock Railway, Splaiul Independentei no. 313, Sector 6, Code 060042, Bucharest, Romania sorinarsene@gmail.com*, ioan_sebesan@yahoo.com DOI: 10.13111/2066-8201.2016.8.2.2 Received: 30 April 2016 / Accepted: 24 May 2016 Copyright©2016. Published by INCAS. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) 4 th International Workshop on Numerical Modelling in Aerospace Sciences, NMAS 2016, 11-12 May 2016, Bucharest, Romania, (held at INCAS, B-dul Iuliu Maniu 220, sector 6) Section 2 – Flight dynamics simulation Abstract: This paper aims to examine the influence of aerodynamic forces acting on the Siemens Desiro railcar, and the percentage of these forces in the total values of resistance to motion. In this regard the numerical simulation of the airflow is used as a method of analysis. We started from the 3D geometric model at a scale of 1:1 of the vehicle bodywork constructive form. The air flow simulation is performed taking into account the speed limits of the vehicle namely 0 km/ h and 140 km/ h, interval in which eight point values are chosen. Key Words: aerodynamic forces, numerical simulation, air flow, railway vehicles, railcar, bodywork 1. INTRODUCTION The two forces acting on engines railway vehicles in motion are on the one hand the traction force generated by the motors axles and the sum of the resistance forces opposing to the movement in the desired direction on the other hand. The values of these forces (corresponding to the moving speed of the vehicle) must to be smaller or equal to the limit of adherence of the wheel- rail contact. Consequently, the mathematical relationship which describes the movement of a motor rail vehicle between two points on a track sector (in traction regime) can be written in accordance with [1-6] as follows:    v a v t v F R F   0 (1) where:  v F 0 tractive force,  v t R total resistance to motion and  v a F limit of adherence force of the wheel -rail contact. The resistance forces acting on a vehicle during its movement in terms of alignment (straight line without level deviation in the vertical direction) depend on multiple frictions, such as: those in the axles bearings, rolling and/ or sliding friction between wheel and the road surface, air friction, friction between the current collector (pantograph, patina) and the contact line and so on. Because of the very large variety of parameters which intervene in the