Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity Σπύρος Βουτσινάς / Spyros Voutsinas

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1 Εθνικό Μεσόβιο Πολυεχνείο National Technical University of Athens Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity Σπύρος Βουσινάς / Spyros outsinas

2 Άδεια Χρήσης Το παρόν εκπαιδευικό υλικό υπόκειαι σε άδειες χρήσης Creative Commons. ια εκπαιδευικό υλικό, όπως εικόνες, που υπόκειαι σε άδεια χρήσης άλλου ύπου, αυή πρέπει να αναφέρεαι ρηώς. Aerodynamics & Aeroelasticity Structural echanics

3 Outline. hat is Aeroelasticity. The framework of Aeroelasticity 3. How aeroelasticity works on ind Turbine blades 4. The program Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 3

4 . hat is Aeroelasticity? Aeroelasticity deals with fluid-structure interactions, In the framework of continuum mechanics this kind of interactions is equivalent to continuity of both kinematics and dynamics. It is similar to that already discussed on connected bodies. One body provides the loads and the other feedbacks the displacements (geometry) and the velocities. In aeroelasticity the role of the one body is taken by the fluid. So the flow provides the loads while the structure feeds back the deformed geometry and its velocity of motion including deformation and rigid body motions. The information provided to the fluid is a direct input to the flow boundary conditions, which specify the flow velocity on a given geometry. Unsteady flows are difficult to calculate in detail. iscous solvers have prohibitively high cost if we would like to use them as design tools. So in aeroelasticity we are interested to get from the flow solver only the required information at the level of detail we need it. Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 4

5 hat is Aeroelasticity? hen the structure is approximated with beams, we only need sectional loads: ift, rag and oment. This suits well to a number of simple or intermediate flow solvers: the BE method, panel methods etc. To this end, we need: Sectional C, C and C distributions as functions of the angle of attack A way to estimate the effective angle of attack and the effective inflow velocity A way to include dynamic inflow especially at higher angles of attack where the aerodynamic response of airfoil section exhibits non-linear behaviour directly linked to viscous effects The first set of information is taken from measurements or CF computations The second is inherently considered in all simplified models The third is provided by semi-empirical models also called dynamic stall models. Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 5

6 . The framework of aeroelasticity Static instabilities Unsteady Aerodynamics CF ynamics Analytic echanics ynamic instability Fatigue aterial Science ulti-body ynamics Thermodynamics Structural amping Structural ynamics CS Control Theory Actuation Technologies Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 6

7 The typical section problem Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 7

8 The typical section problem Aeroelastic Coupling for the airfoil Rotor Plane Torsion Stiffness Pitch Angle Edgewise Bending Stiffness Flapwise Bending Stiffness Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 8

9 3. How aeroelasticity works on T blades Prediction of aerodynamic loading In aeroelastic analysis, aerodynamic loads are introduced based on considerations:. U ( a ) ( Ωr ) ( a ) 5 t f. 5ρ N c ( C cos φ C sin φ ) f t. 5ρ N c ( C sin φ C cos φ ) â φ β tan φ U o ( α ) Ωr( α ) Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 9

10 3. How aeroelasticity works on T blades Including the velocity components due to structural deformations, the flow conditions change Θ y Θ y U F sin( ) cos( ) x y y F cos( ) sin( ) z y y y =C ρ c Nt / m eff =C ρ c Nt / m eff =C ρ c Ntm / m /4 eff tan (a ) (U sin U cos ) (a) (Uwz cos y U sin y ) Ueff,z wz y y U eff,x U U eff eff,x eff,z eff w y Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity

11 3. How aeroelasticity works on T blades ynamic Stall odelling In unsteady aerodynamics we have two effects to take into account: The variation due to wake effects The onset of stall Semi empirical models consider these two effects separately: And for each of the two they define a dynamic equation, st order for the attached part and nd order for that accounting for stall. Of particular interest is the option the ONERA offers by linking the aerodynamic response of airfoils to circulation : C C C It this way it is possible to also consider combined motions such as pitching and heaving as is the case of wind turbine blades (and not only),,... Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity

12 3. How aeroelasticity works on T blades -h -(x c -c/4) θ y θ=θ +θsin(ωt) h=h +hsin(ωt) θ (x c -c/4) θ c/4 h x c = c/ θ θ x c s c ( ) k c c c C lin ( d ) c Clin c s c Note that different circulation parameters are defined for every load. Also note that for and there is no attached circulation parameter. This is because the model directly links it to the corresponding minimum values. Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity

13 Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 3 inearization of the Aerodynamics sinφ cosφ P cosφ sinφ P y p p z p p x lin lin c s c ) d ( C c c C c c k c s ) ( c U y, y y y y Θ Θ U δα Θ U δα c l cos θ sin θ cos α sinα cosφ sinφ c/4 w w p p 3. How aeroelasticity works on T blades

14 Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 4 inearization of the Aerodynamics δα δα δα δα E dα d C C r r a E dα d C C r r a E dα d C C r r a σ a d dα dc a σ λ ) α cos (α dα dc λ ) α sin (α dα dc λ λ lin lin lin 3. How aeroelasticity works on T blades

15 End of presentation Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 5

16 Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 6

17 Aerodynamics & Aeroelasticity: Introduction to Aeroelasticity 7

18 Χρημαοδόηση Το παρόν εκπαιδευικό υλικό έχει αναπυχθεί σα πλαίσια ου εκπαιδευικού έργου ου διδάσκονα. Το έργο «Ανοικά Ακαδημαϊκά Μαθήμαα» ου ΕΜΠ έχει χρημαοδοήσει μόνο ην αναδιαμόρφωση ου υλικού. Το έργο υλοποιείαι σο πλαίσιο ου Επιχειρησιακού Προγράμμαος «Εκπαίδευση και Δια Βίου Μάθηση» και συγχρημαοδοείαι από ην Ευρωπαϊκή Ένωση (Ευρωπαϊκό Κοινωνικό Ταμείο) και από εθνικούς πόρους. Aerodynamics & Aeroelasticity Structural echanics 8