I'm designing an electric fan propulsion system for a hybrid-electric business jet. The hybrid business jet uses a series hybrid configuration and distributed electric propulsion. The electric fan propulsion system is for the distributed electric propulsion part of the engine and consists of the fan, intake duct and propulsive nozzle. So far, I've designed it so that the efficiencies of each component is as close to 1 and optimising the fan pressure ratio so the mass flow rate is large and the exit velocity is small (to improve propulsive efficiency). I'm currently unsure whether there are any other parameters I'm failing to consider and would like some more insight.
Well, if all you care about is the fan performance by itself, then you've pretty much got it. Maximize the component cycle efficiency and maximize the propulsive efficiency and that's it. But if you want to start getting more real-world, then things to think about:
Off design conditions. You can perfectly optimize efficiency at one condition (i.e. for a large commercial airliner this would be cruise: Mach 0.8 @ 40,000 ft), but the thing still has to have acceptable performance at other conditions (e.g. takeoff, Mach 0 @ 0 ft). You may have to compromise on cruise efficiency to get acceptable takeoff performance.
Since this is an electric fan, it will be driven by some kind of a motor. That motor will have some speed where it is most efficient. That may not be the speed at which your fan is most efficient. You'll need to match the two of them to maximize overall aircraft efficiency.
If you want to go even one step further, that electric motor has to get power from somewhere. Presumably a battery. To get peak efficiency from the motor might demand X current at Y voltage, but your battery might be optimized for less than X current. Again, you may need to match the power source to the motor.
If you want to go even further, there are a number of real-world turbomachinery considerations to deal with including: Operability / stall margin, Inlet distortion tolerance (i.e. crosswind), Fan blade aeromechanics (i.e. flutter)