Cavitation has been known for a long time to cause damages in spillways athydropower plants, aerators are therefore often implemented to prevent this.The majority of the hydropower plants in Sweden are installed in the northernpart of the country. In this environment, construction details like vents areexposed to rain, snow, leaves, and other difficult nature conditions for a majorpart of the year. It is therefore of interest to see what will happen if the ventsare sealed.Similar experiments have earlier been investigated at Vattenfall AB, oneof the largest energy companies in Sweden. The investigation consists ofcase studies with multiple variables, closed and open vents, low and highwater levels. The calculations are done with help from computational fluiddynamics and the goal is to see how parameters such as pressure, spreading,and horizontal length change when the aerator is sealed compared to open.The calculations were also carried out in a way so tests in the future can bedone by Vattenfall to validate the results from the computational simulations.The geometry of the hydropower plant is taken from a plant in Skellefteälvenin northern Sweden.