Centrifugal blower, air-blowing apparatus, air-conditioning apparatus, and refrigeration cycle apparatus

A centrifugal air blower comprising:

• a fan including a disk-shaped main plate and a plurality of blades disposed on a peripheral portion of the main plate;
• and
• a scroll casing including:
• a sidewall covering the fan from an axial direction of a rotation axis on which the fan rotates, the sidewall having a suction opening for sucking air;
• a discharge opening for discharging an airflow generated by the fan;
• a tongue portion for guiding the airflow to the discharge opening;
• a peripheral wall surrounding the fan from a radial direction of the rotation axis, the peripheral wall extending in a direction of rotation of the fan from a first end portion of the discharge opening located on a side of the tongue portion to a second end portion of the discharge opening located away from the tongue portion;
• and
• a bell mouth formed along the suction opening of the sidewall,
• wherein
• the bell mouth includes an upstream end and a downstream end, the upstream end being an end portion on an upstream side in a direction of flow of the air passing through the suction opening, the downstream end being an end portion on a downstream side in the direction of flow of the air,
• the upstream end of the bell mouth and the sidewall of the scroll casing are connected to each other by a connecting portion,
• a distance in the radial direction of the rotation axis between the upstream end and the downstream end of the bell mouth is longer at a location where an angle relative to the first end portion of the discharge opening in the direction of rotation of fan is larger, between the first end portion and the second end portion of the discharge opening,
• a position of the upstream end in the axial direction of the rotation axis remains constant,
• the scroll casing includes a curling start portion, a curling end portion, and an opposite portion to the tongue portion,
• the curling start portion is a portion at which the angle relative to the first end portion of the discharge opening in the direction of rotation of the fan is larger than 0 degrees but is smaller than 120 degrees, the curling end portion is a portion at which the angle relative to the first end portion of the discharge opening in the direction of rotation of the fan is larger than 240 degrees but is smaller than 360 degrees, and the opposite portion is a portion at which the angle relative to the first end portion of the discharge opening in the direction of rotation of the fan is larger than 120 degrees but is smaller than 240 degrees,
• the bell mouth has a flat surface portion at at least one of the curling start portion, the curling end portion, and the opposite portion to the tongue portion, and
• at the flat surface portion, the bell mouth has a linear outer contour when viewed from the axial direction of the rotation axis.