Mixing of high momentum flux jets with a confined crossflow is highly relevant in a number of applications related to energy and combustion technology. In this work, the studied application is the combustion air system of the recovery boiler furnace. The objective is to use computational fluid dynamics modeling to systematically study the effects of the main design variables on the mixing, penetration, and evenness of the vertical velocity field. The main new results of this work are: 1) We extend the previous research on mixing of jets with a crossflow to air systems of high momentum flux jets, which are highly relevant for combustion applications. 2) We systematically study the effects of the main design variables on the performance of the air jet system and explore their correlations. 3) We apply the results to the secondary air system of a recovery boiler, which is especially challenging because of the separate injections of fuel and combustion air and the dual role of the recovery boiler as a combustion chamber and a chemical reactor.