A fluid machine for an aircraft engine comprising: a first wall and a second wall circumferentially extending around a central axis; a gaspath defined between the first wall and the second wall; a rotor having blades circumferentially distributed around the central axis and extending across the gaspath, the rotor rotatable about the central axis; and a tandem stator in fluid communication with the rotor and having: a first row of first vanes extending across the gaspath and circumferentially distributed around the central axis, the first vanes having first airfoils including first leading edges, first trailing edges, first pressure sides and first suction sides opposed to the first pressure sides; and a second row of second vanes downstream of the first vanes and extending across the gaspath, the second vanes circumferentially distributed about the central axis, the second vanes having second airfoils including second leading edges, second trailing edges, second pressure sides and second suction sides opposed to the second pressure sides, the first vanes being circumferentially offset from the second vanes; characterised by: depressions defined in the first wall, the depressions extending from a baseline surface of the first wall away from the second wall, a depression of the depressions located circumferentially between a pressure side of the first pressure sides and a suction side of the second suction sides, the depressions axially overlapping the first airfoils and the second airfoils relative to the central axis. a first wall and a second wall circumferentially extending around a central axis; a gaspath defined between the first wall and the second wall; a rotor having blades circumferentially distributed around the central axis and extending across the gaspath, the rotor rotatable about the central axis; and a tandem stator in fluid communication with the rotor and having: a first row of first vanes extending across the gaspath and circumferentially distributed around the central axis, the first vanes having first airfoils including first leading edges, first trailing edges, first pressure sides and first suction sides opposed to the first pressure sides; and a second row of second vanes downstream of the first vanes and extending across the gaspath, the second vanes circumferentially distributed about the central axis, the second vanes having second airfoils including second leading edges, second trailing edges, second pressure sides and second suction sides opposed to the second pressure sides, the first vanes being circumferentially offset from the second vanes; a first row of first vanes extending across the gaspath and circumferentially distributed around the central axis, the first vanes having first airfoils including first leading edges, first trailing edges, first pressure sides and first suction sides opposed to the first pressure sides; and a second row of second vanes downstream of the first vanes and extending across the gaspath, the second vanes circumferentially distributed about the central axis, the second vanes having second airfoils including second leading edges, second trailing edges, second pressure sides and second suction sides opposed to the second pressure sides, the first vanes being circumferentially offset from the second vanes;