A compound engine assembly comprising: a compressor; an engine core including at least one internal combustion engine each having a rotor sealingly and rotationally received within a respective internal cavity to provide rotating chambers of variable volume in the respective internal cavity, the engine core having an inlet in fluid communication with an outlet of the compressor; a turbine section having an inlet in fluid communication with an outlet of the engine core, the turbine section configured to compound power with the engine core; and an air conduit having at least one heat exchanger (72, 74) extending thereacross such that an airflow through the air conduit circulates through the at least one heat exchanger (72, 74), each of the at least one heat exchanger (72, 74) configured to circulate a fluid to be cooled in heat exchange relationship with the airflow circulating therethrough; characterized in that the air conduit has opposed inlet and outlets (68, 76) in fluid communication with ambient air around the compound engine assembly; and in that an outer wall of the air conduit has a plurality of openings defined therethrough downstream of the at least one heat exchanger (72, 74), each of the plurality of openings being selectively closable by a respective pivotable flap movable between a retracted position where the opening is obstructed and an extended position away from the opening, each of the plurality of openings defining a fluid communication between the air conduit and the ambient air around the compound engine assembly when the respective pivotable flap is in the extended position. a compressor; an engine core including at least one internal combustion engine each having a rotor sealingly and rotationally received within a respective internal cavity to provide rotating chambers of variable volume in the respective internal cavity, the engine core having an inlet in fluid communication with an outlet of the compressor; a turbine section having an inlet in fluid communication with an outlet of the engine core, the turbine section configured to compound power with the engine core; and an air conduit having at least one heat exchanger (72, 74) extending thereacross such that an airflow through the air conduit circulates through the at least one heat exchanger (72, 74), each of the at least one heat exchanger (72, 74) configured to circulate a fluid to be cooled in heat exchange relationship with the airflow circulating therethrough; characterized in that the air conduit has opposed inlet and outlets (68, 76) in fluid communication with ambient air around the compound engine assembly; and in that an outer wall of the air conduit has a plurality of openings defined therethrough downstream of the at least one heat exchanger (72, 74), each of the plurality of openings being selectively closable by a respective pivotable flap movable between a retracted position where the opening is obstructed and an extended position away from the opening, each of the plurality of openings defining a fluid communication between the air conduit and the ambient air around the compound engine assembly when the respective pivotable flap is in the extended position.