This paper has attempted to compile the assessment of flow field and aerodynamic forces acting on a small straight-bladed vertical axis wind turbine (VAWT). Two dimensional unsteady flows around the VAWT, operating at three different tip speed ratios in a wind tunnel, were investigated through the use of a Laser Doppler Velocimeter (LDV) system. Furthermore, in order to explicate the characteristics of aerodynamic forces, pressures acting on the blade surface were measured during the rotation by a multiport scanner mounted on the hub and pressure signals were transmitted to the stationary system through a wireless LAN. Velocity distribution proved the wind velocity deficit. While, the geometrical angle of attack and resultant flow velocity change periodically due to local wind velocity and direction depending on the azimuth angle. The power coefficient, tangential force, lift and drag which are obtained by pressure distribution are discussed as a function of blade azimuthally position, achieving a numerical quantification of the influence of tip speed ratio on overall rotor performance. As a result, it is clarified that aerodynamic forces show the maximum values when the blade passes through the upstream region. (C) 2016 Elsevier Ltd. All rights reserved.