A gas turbine engine comprising: a rotor including an array of circumferentially spaced blades configured for rotation; and an annular inlet including an axially extending wall having a central longitudinal axis, the wall having an upstream end located upstream of the blades, a downstream portion surrounding the blades in proximity of tips of the blades, and an inlet wall portion extending axially from the upstream end to the downstream portion, the inlet wall portion defining an inlet flow path for directing air to the blades, the inlet wall portion having a shape defining a plurality of teeth circumferentially spaced around the inlet, the teeth extending axially, the teeth projecting radially inwardly toward the central longitudinal axis, a central portion of the inlet flow path having a cross-sectional dimension measured diametrically between opposed ones of the teeth, the cross-sectional dimension varying along the axial direction, the central portion defining a geometric throat at a minimum value of the cross-sectional dimension, the inlet wall shaped so that the geometric throat is axially spaced from the upstream end and the blades, characterised in that: a cross-sectional area of the inlet flow path surrounded by the inlet wall portion varies along the axial direction, the inlet wall defining an aerodynamic throat at a minimum value of the cross-sectional area, the inlet wall shaped so that the geometric throat is axially spaced from the aerodynamic throat. a rotor including an array of circumferentially spaced blades configured for rotation; and an annular inlet including an axially extending wall having a central longitudinal axis, the wall having an upstream end located upstream of the blades, a downstream portion surrounding the blades in proximity of tips of the blades, and an inlet wall portion extending axially from the upstream end to the downstream portion, the inlet wall portion defining an inlet flow path for directing air to the blades, the inlet wall portion having a shape defining a plurality of teeth circumferentially spaced around the inlet, the teeth extending axially, the teeth projecting radially inwardly toward the central longitudinal axis, a central portion of the inlet flow path having a cross-sectional dimension measured diametrically between opposed ones of the teeth, the cross-sectional dimension varying along the axial direction, the central portion defining a geometric throat at a minimum value of the cross-sectional dimension, the inlet wall shaped so that the geometric throat is axially spaced from the upstream end and the blades, characterised in that: a cross-sectional area of the inlet flow path surrounded by the inlet wall portion varies along the axial direction, the inlet wall defining an aerodynamic throat at a minimum value of the cross-sectional area, the inlet wall shaped so that the geometric throat is axially spaced from the aerodynamic throat. an upstream end located upstream of the blades, a downstream portion surrounding the blades in proximity of tips of the blades, and an inlet wall portion extending axially from the upstream end to the downstream portion, the inlet wall portion defining an inlet flow path for directing air to the blades, the inlet wall portion having a shape defining a plurality of teeth circumferentially spaced around the inlet, the teeth extending axially, the teeth projecting radially inwardly toward the central longitudinal axis, a central portion of the inlet flow path having a cross-sectional dimension measured diametrically between opposed ones of the teeth, the cross-sectional dimension varying along the axial direction, the central portion defining a geometric throat at a minimum value of the cross-sectional dimension, the inlet wall shaped so that the geometric throat is axially spaced from the upstream end and the blades, characterised in that: a cross-sectional area of the inlet flow path surrounded by the inlet wall portion varies along the axial direction, the inlet wall defining an aerodynamic throat at a minimum value of the cross-sectional area, the inlet wall shaped so that the geometric throat is axially spaced from the aerodynamic throat.