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Projecte llegit

Títol: Flow separation modelling through discrete vortex methods

Estudiants que han llegit aquest projecte:

Director/a: VILLARDI DE MONTLAUR, ADELINE DE

Departament: FIS

Títol: Flow separation modelling through discrete vortex methods

Data inici oferta: 13-12-2011     Data finalització oferta: 13-07-2012


Estudis d'assignació del projecte:
    Tipus: Individual
     
    Lloc de realització: Fora UPC    CIMNE
     
            Supervisor/a extern: Jordi Pons Prats
            Institució/Empresa: CIMNE
     
    Paraules clau:
    flow separation, discrete vortex methods, aeroelastic effects
     
    Descripció del contingut i pla d'activitats:
    Objectives of the MT:
    – Implementation of a low order panel method for airfoil (2D) computations.
    – Model flow separation by using discrete vortex methods.
    – Coupling of the code with a structural, two degree of freedom model in order to study aeroelastic effects.
    – Extension of the code to 3D models.

    Methodology used:
    – The low order panel method will be implemented using a classical model: A combination of sources and doublets, which allows the computation of thick, cambered airfoils and leads to
    quite good results with an easy implementation.
    – Two different models will be implemented in order to introduce separation effects on the airfoil:
    * Vortex cloud method, where a sheet of vorticity points is generated over the airfoil surface every time step, leading them afterwards freely to move, convect and stretch in the flow field.
    * Fixed point vorton generation method, where only a single vorticity element is generated every time step in the separation point. The difficulty in implementing this method consists in the need to define a condition of separation in order to compute the position of the separation point.
    – Once the method works, a simple structural model based on two degrees of freedom, torsion and vertical displacement, will be implemented in order to study aeroelastic effects such as
    flutter and divergence. This step will allow the validation of the code assessing also the basis for the coupled structural-aerodynamic computations, which are necessary in order to
    implement properly the next step.
    – Improvement of the code. This task will be done in the following directions:
    * Introduction of compressibility effects in order to enlarge the range of airflow speeds where the model is still valid.
    * Translation of this theory to 3D models. The difficulty of this step lies on the fact that, even if equations may be the same, geometric conditions to be set become more complex.

    Other informations:
    – This project will be dedicated to improve an actual tool which is yet computing solutions for flexible structures in a commercial way.
     
    Overview (resum en anglès):
    The objective of the present Master thesis is to develop a flow separation model for airfoils (2D problems) in order to overcome the limitations of classical potential models where flow separation is not allowed. This is done through a meshless methodology called full cloud vortex method.

    This method computes the solution in several steps. First one, the airfoil is discretized in panels and through classical potential methods, the vorticity over each
    panel is obtained. After that, the vorticity is concentrated in a single point and shed at a certain distance of the panel.
    Next step consists on the convection of this vorticity points under the influence of the flow field, the panels and the other vortices. In order to increase the accuracy, the final position is obtained from the computed velocity through a forward 2nd order integration method.
    In order to cope also viscous effects, a simple method to compute the diffusion of the vorticity of each shed vortex is also implemented.
    Finally, the pressure coefficient of each panel and the forces acting on the whole airfoil are computed.
    Once the forces are obtained, a dynamic analysis is carried on. In order to do that, a simple 2 degrees of freedom spring-mass-damper model is implemented. From it, the
    position, velocity and acceleration of every node of the discretized airfoil is computed.
    The velocities and accelerations are obtained through a 2nd order finite differences scheme.
    All the equations are implemented in Fortran, and the final program is introduced in a pre-post processor called GiD, which allows to generate the geometry, discretize it
    and set all the needed parameters up for for running the simulations.
    Finally, in order to test the code, three geometries are tested: A cylinder, a symmetric airfoil (NACA0012) and a non symmetric airfoil (NACA4412). The results obtained are compared with experimental results in order to check the correct behaviour of the code.
    In all the 3 simulated geometries, the results are in good agreement with the experimental ones.

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