Fluid machine, wind turbine, and method for increasing velocity of internal flow of fluid machine, utilizing unsteady flow

A wind turbine comprising a casing having an annular shape and an axial cross-section of a non-streamline shape, and an impeller disposed at a throat section inside the casing to rotate around an axis, wherein wind turbine is configured to split a surrounding flow into an internal flow and an external flow at a front edge and to force the flows to cause separations, such that vortex streets are formed downstream of the casing by the separations, and a negative pressure region having a cell structure in an annular direction is formed by the vortex streets and vortex street fluctuations, whereby a velocity of the internal flow inside the casing is increased,

• wherein a reference line serving as a reference for forming the thickness of the casing connects the front edge and a rear edge in the axial cross-section, and includes a cycloid curve having a convex portion at the throat section between the front and rear edges,
• the throat section and a vortex generating portion disposed downstream
• of the throat section to generate the negative pressure region are formed on a radially inner circumferential face of the casing, a first outflow gradient is formed on an outer circumferential face of the casing and at the rear edge to separate the external flow at the rear edge, and a second outflow gradient is formed on a throat-side adjacent face adjacent to the vortex generating portion and at a boundary between the throat-side adjacent face and the vortex generating portion to separate the internal flow,
• the first outflow gradient is equal to or larger than a gradient of a conical generatrix line connecting the front edge and the rear edge, and the second outflow gradient is equal to or smaller than a reference gradient, the reference gradient being a gradient of a front end of the vortex generating portion when the reference cycloid curve forms the inner circumferential face, and
• the negative pressure region of high vorticity is generated behind the vortex generating portion by virtue of the non-streamline shaped casing to increase the velocity of the internal flow.

A method for increasing a velocity of an internal flow by utilizing an unsteady flow, the method comprising providing an impeller inside a casing having an annular shape and having an axial cross-section of a non-streamline shape, splitting a surrounding flow into an internal flow and an external flow at a front edge and to force the flows to cause separations, forming vortex streets downstream of the casing by the separations, and forming a negative pressure region having a cell structure in an annular direction by the vortex streets and vortex street fluctuations, thereby increasing the velocity of the internal flow inside the casing, the method further comprising:

• forming a reference line serving as a reference for forming the thickness of the casing as a cycloid curve connecting the front edge and a rear edge in the axial cross-section and having a convex portion at a throat section between the front and rear edges,
• forming the throat section and a vortex generating portion on a radially inner circumferential face of the casing, the vortex generating portion being downstream of the throat section to generate the negative pressure region, forming a first outflow gradient on an outer circumferential face of the casing and at the rear edge to separate the external flow at the rear edge, forming a second outflow gradient on a throat-side adjacent face adjacent to the vortex generating portion and at a boundary between the throat-side adjacent face and the vortex generating portion to separate the internal flow,
• setting the first outflow gradient to be equal to or larger than a gradient of a conical generatrix line connecting the front edge and the rear edge, setting the second outflow gradient to be equal to or smaller than a reference gradient, the reference gradient being a gradient of a front end of the vortex generating portion when the reference cycloid curve forms the inner circumferential face, and
• generating the negative pressure region having high voracity behind the vortex generating portion by virtue of the non-streamline shaped casing to increase the velocity of the internal flow.