Turbomachinery

Synthetic program:

descrizione delle turbomacchine. Elementi di fluidodinamica e termodinamica. Similitudine idraulica con estensione a flussi comprimibile. Flusso nelle turbomacchine: equazioni del moto, effetti di schiera, equilibrio radiale, flussi secondari. Compressori assiali: ottimizzazione degli stadi, aerodinamica dei profili e criteri di carico, valutazione delle perdite. Compressori centrifughi: criteri di progetto di rotore, diffusore a voluta; fattore di scorrimento e perdite. Pompaggio e stallo nei compressori. Turbine assiali: ottimizzazione, criteri di carico, valutazione delle perdite. Raffreddamento nelle turbine a gas. Forzanti aerodinamiche.

Topic 1 – Fundamentals of Aerodynamics, Thermodynamics and Turbomachinery Flow: Stresses in continuum media. Mass conservation equation, momentum balance, energy balance for open systems (all balances are discussed in both differential and integral forms). Equation for one-dimensional flows and for 2D - 3D complex flows in the stationary and rotating frame of reference. Lift and drag on profiles and blades. Viscous and turbulent flows; boundary layer. Principle and basic equations for thermodynamics, thermodynamic process representation, loss coefficient and efficiency parameters. Euler equation and reaction degree.

Topic 2 – Operation of Turbomachinery: general performance curves, Model Theory and Similarity for incompressible flows. Turbomachinery classification on the basis of specific speed and specific diameter. Compressibility effects on the similarity laws for gas/steam turbines and compressors.

Topic 3 – Turbomachinery fluid-dynamics : Unsteady aspects, different frames of reference. Projection on reference surfaces (blade to blade, meridional and secondary ones), main geometrical and fluid-dynamic quantities for turbomachinery cascades. Cascade effects. Radial equilibrium. Secondary flows, 3D effects, clearances and wake effects. Clearances geometries and design. 2D and 3D blade design concepts.

Topic 4 – Diffusers: geometries and operation for compressible and incompressible flows. Shape factor and main performance parameters.

Topic 5 – Axial Compressors: classification and analysis according to 1D approach. Blade aerodynamics. Prediction of flow angle, losses and blades number by semi-empirical criteria. Blade loading criteria. Supersonic and chocked cascades. Off design operation.

Topic 6 – Radial Compressors: classification and analysis according to 1D approach. Slip factor. Losses in rotors and their geometry. Free vortex diffusers for subsonic and supersonic operation. Volute design.

Topic 7 –Compressors Instability: Helmholtz theory. Blade stall and rotating stall. Surge and machine – plant interaction.

Topic 8 – Turbines: classification and analysis according to 1D approach for different reaction degrees. Discussion on optimisation parameters. Semi-empirical criteria for flow angle and losses prediction downstream subsonic and supersonic cascades. Blade loading criteria. Gas turbines: blade cooling, thermal aspects for cooled blade, aero-engine architecture.

Topic 9 – Computational schemes for Turbomachinery: lumped parameter approach, 1D-2D and 3D schemes, issues for unsteady solutions.

Topic 10 – Mechanical issues for Turbomachinery blades: periodic aerodynamic forcing, aero-elastic effects, flutter, mechanical damping.