A combustor for a rotating detonation engine includes an outer tapered wall extending along an axis; an inner tapered wall extending along the axis, wherein the inner tapered wall is positioned within the outer tapered wall to define an annular combustion chamber having an annular gap between the outer tapered wall and the inner tapered wall, wherein the outer tapered wall is moveable relative to the inner tapered wall along the axis, and wherein movement of the outer tapered wall relative to the inner tapered wall changes the annular gap of the annular combustion chamber. Obstacles can be positioned on either or both of inner and outer wall to enhance turbulence within the combustion chamber.