Secondary Flows in Turbine Cascades & Consequences

P M V SubbaraoProfessor

Mechanical Engineering Department

Finite Length of Blade Generates more Physical Boundaries and vorticity.……

Parts of A Current Turbine Rotor

Losses Contributed by EndWalls

More Geometrical Features of A Turbine Blade

Modular Concept of Blade Design & Construction

The Profile of A 3D Blade

• A 3D blade works along with its endwalls.

• Endwall flows originate from specifically developing endwall boundary layers.

• These are associated with the presence of longitudinal vortices with a dominant streamwise component of the vorticity.

• These are generally known as and secondary flows.

• They are driven by transverse static pressure gradients and mass forces acting on fluid elements in curvilinear motion through the blade-to-blade passage.

Understanding the complex development of endwall flows is a part of betterment of blade profile !!!

Impact of Endwall Flows

• Endwall flows are also an important source of losses in turbines.

• More serious impact on cascades with short-height blading and high flow turning.

• Due to the complex nature of endwall boundary layer flows/secondary flows, the evaluation of endwall losses is not an easy task.