Rapid increase in global energy requirements has resulted in considerable attention towards energy generation from the renewable energy sources. In order to meet renewable energy targets, harnessing energy from all available resources including those from urban environment is required. Vertical Axis Wind Turbines (VAWTs) are seen as a potential way of utilising urban energy sources. Most of the research on the wind turbines constitutes condition monitoring and performance optimisation of VAWTs under a constant velocity of air where the transient effects have not been accounted. The inconsistent behaviour of the wind may change the nature of the flow field around the VAWT which could decrease its life cycle. This study is an attempt to use Computational Fluid Dynamic’s techniques to study and analyse the performance of a wind turbine under accelerating and decelerating air inlet velocity. The performance of a VAWT is monitored under an accelerated and decelerated gust of the value 1.09m/s² characterised by change in velocity from 4m/sec to 10m/sec. The instantaneous torque output varies significantly when a gust of air is applied to the turbine. Furthermore the torque outputs during accelerating and decelerating flows vary, highlighting the effect of transient phenomena. This abrupt change in the instantaneous torque output of the turbine may give rise to highly transient loads on the turbine’s structure which may induce heavy stresses on the turbine leading to structural failure. It has been shown that CFD can be used as an effective tool to predict the performance outputs of a VAWT under varying flow conditions.