Turbine housing and variable geometry turbocharger

A turbine housing for accommodating a turbine rotor, comprising:

• a scroll passage forming part which forms a scroll passage extending along a circumferential direction around an axis of the turbine rotor;
• a nozzle passage forming part which forms a nozzle passage for directing exhaust gas from the scroll passage to the turbine rotor disposed on an inner peripheral side of the scroll passage, the nozzle passage forming part having a shroud-side passage wall surface and a hub-side passage wall surface which define the nozzle passage;
• and
• a variable nozzle unit for adjusting a flow of the exhaust gas in the nozzle passage, the variable nozzle unit including at least one nozzle vane disposed in the nozzle passage,
• wherein the scroll passage forming part includes a scroll passage wall surface connecting an outer peripheral end of the scroll passage and an outer peripheral end of the hub-side passage wall surface,
• wherein, in a cross-section along the axis passing through a tongue portion of the scroll passage forming part, the scroll passage wall surface includes:
• a first arc portion connected at an outer peripheral end to the outer peripheral end of the scroll passage and extending from the outer peripheral end inward in a radial direction of the turbine rotor;
• and
• a cliff portion connected at one end to an inner peripheral end of the first arc portion and connected at another end to the outer peripheral end of the hub-side passage wall surface, the cliff portion including a second arc portion connected to the inner peripheral end of the first arc portion and forming an inflection point between the first arc portion and the second arc portion,
• wherein the inflection point is located offset frontward from the outer peripheral end of the hub-side passage wall surface in an axial direction of the turbine rotor and outward from the outer peripheral end of the hub-side passage wall surface in the radial direction, and
• wherein, when a length in the axial direction between the one end and the another end of the cliff portion is defined as X, the length X gradually decreases toward a downstream side of the scroll passage.