A turbine includes a housing including an inlet, an outlet, and a shroud section having a shroud surface extending between the inlet and the outlet; and a turbine impeller housed in the housing and including a hub and a plurality of blades disposed on an outer peripheral surface of the hub, each of the blades having a side edge extending along the shroud surface. The side edge of each of the blades has a side-edge upstream portion disposed on a side of the inlet, and a side-edge downstream portion disposed on a side of the outlet. The shroud surface has a shroud upstream portion disposed on the side of the inlet and extending along the side-edge upstream portion, and a shroud downstream portion disposed on the side of the outlet and extending along the side-edge downstream portion. The shroud upstream portion has a meridional cross-sectional shape whose inclination angle (θ 1 ) with respect to an axis (L) of the hub at the side of the inlet is smaller than in a case where the shroud upstream portion has a meridional cross-sectional shape of an arc shape and the shroud downstream portion has a meridional cross-sectional shape of a linear shape along a direction of the axis of the hub.
1. A turbine, comprising:
a housing including an inlet, an outlet, and a shroud section having a shroud surface extending between the inlet and the outlet; and
a turbine impeller housed in the housing and including a hub and a plurality of blades disposed on an outer peripheral surface of the hub, each of the blades having a side edge extending along the shroud surface,
wherein the side edge of each of the blades has
a side-edge upstream portion disposed on a side of the inlet, and
a side-edge downstream portion disposed on a side of the outlet,
wherein the shroud surface has
a shroud upstream portion disposed on the side of the inlet and extending along the side-edge upstream portions of the blades, and
a shroud downstream portion disposed on the side of the outlet and extending along the side-edge downstream portion, and
wherein the shroud upstream portion has a meridional cross-sectional shape having a curvature radius R defined by following expression 1:
R
≧
(
R
1
-
R
2
t
)
2
+
Ls
2
2
(
R
1
-
R
2
t
)
where R 1 is a distance in a radial direction from an axis of the hub to the inlet, R 2 t is a distance in the radial direction from the axis of the hub to the outlet, and Ls is a length of the shroud surface in a direction of the axis of the hub, and
wherein the shroud downstream portion has a meridional cross-sectional of an arc shape having a curvature radius R defined by following expression 2:
R
=
(
R
1
-
R
2
t
)
2
+
Ls
2
2
(
R
1
-
R
2
t
)
.
2. The turbine according to claim 1 ,
wherein a ratio Ls/D 1 of the length Ls to an inner diameter D 1 is greater than 0.16, provided that D 1 is an inner diameter of the shroud at the inlet.
3. The turbine according to claim 1 ,
wherein a ratio of a distance R 2 t to a distance R 1 is not more than 0.95, provided that R 1 is a distance in a radial direction from the axis of the hub to the inlet, and R 2 t is a distance in the radial direction from the axis of the hub to the outlet.