A seal assembly

An axial flow turbine according to claim 1, wherein the fluid jet outlet is configured to admit the second fluid into the fluid leakage cavity in an upstream direction which is inclined to the turbine axis so as to partially oppose the flow of the first fluid through the fluid leakage cavity.

An axial flow turbine according to claim 1, wherein the second fluid is ejected from the fluid jet outlet so as to be initially admitted into the fluid leakage cavity in an upstream direction having an axial component and a radial component.

An axial flow turbine according to claim 1, wherein the fluid jet outlet is defined by a wall of the housing which lies radially outboard of the turbine rotor.

An axial flow turbine according to claim 1, wherein the pressure of the second fluid exiting the fluid jet outlet is greater than the pressure of the first fluid passing the fluid jet outlet.

An axial flow turbine according to claim 1, wherein the pressure of the second fluid exceeds a threshold required to cause the second fluid to cross at least around half of the radial width of the fluid leakage cavity before it has turned to flow in an axial direction.

An axial flow turbine according to claim 1, wherein the first flow restriction is located downstream of the fluid jet outlet and at a location such that, in use, second fluid admitted from the fluid jet outlet would impinge on the first flow restriction once the second fluid has turned to flow in an axial direction under the influence of flow of the first fluid through the fluid leakage cavity.

An axial flow turbine according to claim 1, wherein the first flow restriction is spaced from the centre of the fluid jet outlet by a distance that is one of (i) approximately one half to twice the radial width of the fluid leakage cavity and (ii) approximately the same distance as the radial width of the fluid leakage cavity.

An axial flow turbine according to claim 1, wherein the first flow restriction is located on an opposite side of the fluid leakage cavity to the side from which the second fluid is admitted into the fluid leakage cavity via the fluid jet outlet.

An axial flow turbine according to claim 1, wherein the first flow restriction is provided on the radially inboard side of the fluid leakage cavity and the fluid jet outlet is provided on the radially outboard side of the fluid leakage cavity.

An axial flow turbine according to claim 1, wherein the first flow restriction is a projection extending radially outwards from the radially outer periphery of the turbine rotor.

An axial flow turbine according to claim 1, wherein the first flow restriction extends across one of (i) up to around 90% of the radial width of the fluid leakage cavity, (ii) at least 5% of the radial width of the fluid leakage cavity, or (iii) up to around 90% of the radial width of the fluid leakage cavity and at least 5% of the radial width of the fluid leakage cavity.

An axial flow turbine according to claim 1, wherein the first flow restriction is defined by a section of the turbine rotor downstream of the fluid jet outlet.

An axial flow turbine according to claim 1, wherein the second flow restriction is defined by a section of the wall of the housing downstream of the first flow restriction which lies one of (i) radially closer to the turbine rotor than the section of the wall of the housing which defines the fluid jet outlet, (ii) axially closer to the turbine rotor than the section of the wall of the housing which defines the fluid jet outlet, or (iii) radially and axially closer to the turbine rotor than the section of the wall of the housing which defines the fluid jet outlet.

An axial flow turbine according to claim 14, wherein the second flow restriction is an axial clearance between a radially extending section of the wall of the housing and a radial surface of the downstream end of the turbine shroud, the axial clearance being of smaller dimension than the radial width of a section of the fluid leakage cavity between the housing and the radially outer periphery of the turbine rotor.

A turbomachine comprising an axial flow turbine according to claim 1.

A waste heat recovery system comprising an axial flow turbine according to claim 1.

A seal assembly for restricting fluid leakage flow through a fluid leakage cavity defined between a first component and second component that is rotatable about an axis relative to the first component, the seal assembly comprising:

• a fluid jet outlet configured to admit a fluid jet into the fluid leakage cavity in an upstream direction which is inclined to the axis,
• a first flow restriction located downstream of the fluid jet outlet and at a location such that the fluid jet admitted from the fluid jet outlet would impinge on the first flow restriction once the fluid jet has turned to flow in an axial direction, and
• a second flow restriction located downstream of the first flow restriction.