An air blowing device for cooling an internal combustion engine of a vehicle tested on a roller bench, including an air blowing fan configured to blow air towards the air intake opening provided on the vehicle to direct an air stream towards members cooling the engine, including a nozzle arranged between the outlet opening of the air blowing fan and the opening provided on the vehicle. The nozzle has a cross-section relative to the air stream gradually tapering between the outlet opening of the fan and the inlet opening of the vehicle. The nozzle includes two side walls each having an opening allowing a strap to pass, wherein one of the ends is configured to be attached to the vehicle and the other end is configured to be attached to a fixed vertical wall arranged proximate the outlet of the fan.