DC shunt generators problem
Almost in every generator the quantity that's regulated at the output is always voltage, so if you change the load, the current will change but the voltage remains same(or it's supposed to remain same, ideally), and when you say it's a DC generator the the output voltage is Direct, not Alternating.

If you're confused as to how a rotating machine produce a unidirectional and almost constant voltage, it's because of the shape of the poles, they are arranged so that the field on the armature windings remains almost constant-in magnitude and direction as well- but there's one more problem, when armature winding goes from beneath of one pole to another, the voltage suddenly changes direction at the terminals of the armature(magnitude still remains same), but that's one of the reason why commutators are used, to prevent the polarity reversal- and also to deliver power out of the rotating structure.