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Projecte llegit

Títol: Numerical analysis of airfoil hysteresis at high Reynolds numbers

Estudiants que han llegit aquest projecte:

Director/a: MELLIBOVSKY ELSTEIN, FERNANDO PABLO

Departament: FIS

Títol: Numerical analysis of airfoil hysteresis at high Reynolds numbers

Data inici oferta: 27-01-2025     Data finalització oferta: 27-09-2025


Estudis d'assignació del projecte:
    GR ENG SIST AEROESP
Tipus: Individual
 
Lloc de realització: EETAC
 
Paraules clau:
Hysteresis, airfoil, aerodynamics, NekRS, RANS, bistability
 
Descripció del contingut i pla d'activitats:
 
Overview (resum en anglès):
Understanding the hysteresis phenomenon around airfoils plays a crucial role in aerodynamics and it is essential for predicting the flow behavior especially at high Reynolds numbers, which are commonly encountered in real life applications. With this premise, this study investigates the presence of this phenomenon around a NACA0012 airfoil at a Reynolds number of one million. To achieve the upstroke and downstroke solutions, simulations are initialized from previous converged solutions with increments of 0.25º in the angle of attack. These simulations are carried out using the high-order spectral element solver NekRS, employing the RANS equations as the turbulence model.

Before conducting the main simulations, the numerical setup is validated through a mesh convergence analysis, ensuring the results are not dependent on the mesh or the domain employed. After the upstroke and the downstroke cases are simulated, the hysteresis loop has been identified in the range of angle of attack from 15.5º to 20º, showing significant differences for the two paths regarding aerodynamic forces, boundary layer separation points, separation bubbles and vortex shedding. An in-depth analysis is done, focusing on some of the most relevant angles of attack, and the results are also compared to previous work in the field.


Additionally, to further understand the hysteresis phenomenon, the edge tracking method is employed to investigate the basin boundary between the two stable states found for the same angle of attack. Using a bisection method, the edge state has been narrowed down to a range of the mixing parameter, which defines the proportion of each solution (upstroke and downstroke) in the linear combination used as the initial condition. Interestingly, within this narrow interval, slight variations of the mixing parameter led to alternating outcomes, suggesting a potentially fractal structure of the basin boundary. Furthermore, the transient behavior of different simulations is examined, as it provides insight into the characteristics of the edge state. The flow fields observed during these transients exhibit intermediate characteristics, distinct from both stable solutions they originate from, indicating the existence of an unstable solution that lies on the boundary between both basins of attraction.

These findings contribute to a deeper understanding of aerodynamic hysteresis and bistability, offering valuable insight into the dynamic behavior of the flow at high Reynolds numbers.

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