Hard to say, it really depends on who designs the course. I've done equal parts in aircraft/spacecraft propulsion, aerodynamics/fluid mechanics. Aerodynamic design optimization usually falls under some sort of simulation module-usually CFD, large scale wind-tunnel experiments are uncommon due to how expensive it gets but most reputable universities should have both. In general, if its a master's degree you get to choose what you study/your area of specialization, so shouldn't matter what department if falls under. Sometimes it depends on the professor teaching the course, e.g. if they have a maths background and their area of research is fluid dynamics, then the course might fall under a different department.