GE Aeroderivative Gas Turbines are derived from GE’s Aircraft engine family and converted to Land and Marine applications. As these Aeroderivative Gas Turbines are relatively smaller in size for similar power capacity in comparison to Heavy Duty Gas Turbines, there is a great need of developing efficient and compact turbine enclosure ventilation system for proper cooling and ventilation. Ineffective ventilation flow distribution inside the gas turbine enclosure causes engine circumferential nonuniform temperature distribution and it allows the formation of explosive fuel gas pockets inside the enclosure in the unlikely event of fuel leaks. Also, the engine nonuniform circumferential temperature gradient has an adverse impact on the operational efficiency and/or the mechanical integrity of the turbine. Proper cooling and ventilation system will also protect the sensitive equipment, like fuel valve actuators or any other instruments inside the turbine enclosure due to excessive radiation heat from engine hot surfaces, mainly near combustor and power turbine region. All the expected but significant engine leakages into the enclosure are estimated and considered for selection of right size, type, placing of ventilation fan at different operating conditions like full load, part load, elevation and ambient conditions. For first step, a 3D Computational Fluid Dynamics (CFD) analyses were done for turbine enclosure with mass/volumetric flow rate, temperature, and pressure boundary conditions to understand the flow/temperature distribution inside the enclosure. Radiation boundary conditions are applied on the engine casing external surfaces, enclosure walls and roof. The convective heat transfer from the hot surfaces are computed by CFD model based on the velocity and temperature predictions. In next step, from CFD analysis, identified the poor ventilation/stagnation zones using low velocity and recirculation areas close to the gas fuel components. After identifying the poor ventilation regions, a gas leak was introduced to see whether gas cloud volume is within the ISO 21789 – 2009 limits. From gas leak analysis results, enclosure outlet IR detector settings were decided and implemented to monitor the gas leak amount and feedback to control system in the form of ALARM/SHUTDOWN so that Gas Turbine operates safely.