33927 - Machines M

Course contents

Multiple extraction steam power plants. Optimization of steam extraction pressure. Three extraction steam power plant. Governing equations in the exchangers and power equation, T-s and Mollier thermodynamics diagrams.

Compressible flow turbomachines. Static and total quantities. Equations of fluid motion in moving channels. The speed of sound and flow regimes. Compressible fluid flow equations. The chocking. Stodola Ellipse. Link between transversal area and flow in a channel depending on the regime of motion: Hugoniot equation. Euler equation and equation with the differences of kinetic energy for a rotor row. Shock wave, the equations that manage the shock wave. Mach numbers at the exit of shock wave as a function of the Mach number entering the shock wave. inlet Pressure as a function of the outlet shock wav. Entropy variation in the  shock wave. Fanno and Reyleight curves.

The impulse stage: the velocity triangles, the maximum work, physical states on the enthalpy diagram.

The axial turbines reaction stage; velocity triangles, degree of reaction, maximum work, total to total efficiency, total to static efficiency, representation of physical states in the enthalpy diagram.

The De Laval Turbine and limitations on the enthalpy change. Curtis wheel and its velocity triangles. Efficiency evaluation for one, two and three velocity stages. The pressure stage turbine and the recovery factor. The reaction turbine. Limits on input and output volumetric flow of a reaction turbine. The mixed and double flow turbines.

Analytical determination of the performance curves of an axial compressor stage.

Turbine-compressor coupling and gas turbine off-design. VIGV and VNGV applications. Two-shaft gas turbine plant architecture. Off-design of gas turbine power plants and main strategies of plant management (TIT and TOT constant).

Influence of ambient temperature on the performance of a gas turbine. Several solutions to lower the inlet compressor temperature: Fogging strategies.

 

Pelton Turbine. Scheme and operating principle. Inlet and outlet rotor velocity triangles. Maximum work, off-design and characteristic curves.

Specific speed. Mechanical, kinematical, dynamical and geometrical similarity: hydraulic similarity. Specific diameter and non-dimensional impeller speed.

Francis Turbine. Scheme and operating principle. Degree of reaction. Inlet and outlet rotor velocity triangles. Maximum work, flow condition, off-design and characteristic curves. Balance of the axial forces on the turbine rotor and design solutions. Importance of  the discharge duct in a Francis turbine plant and description of the outlet pressure trend as a function of design parameters at the duct outlet.  Rotor shape improvements as a function of specific speed in (high flow rate and low head). The cavitation problem and Thoma number definition. Description of the sudden off-design problems and solutions.

Propeller and Kaplan Turbine. Scheme and operating principle. Inlet and outlet rotor velocity triangles from hub to tip of the impeller. Off-design and characteristic curves. Kaplan Turbine, operating principle.

 

Readings/Bibliography

"Sistemi Energetici" 1 – MACCHINE A FLUIDO, G: Negri di Montenegro, M. Bianchi A. Peretto – Pitagora Editore

"Sistemi Energetici" 2 – COMPLEMENTI, M. Bianchi, F. Melino, A. Peretto – Pitagora Editore

Appunti di Macchine Idrauliche

Office hours

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