Dynamic mesh framework for morphing wings CFD

Abdessemed, Chawki

Abstract

In this work, a framework to perform high fidelity Computational Fluid Dynamics (CFD) analysis of dynamically morphing airfoils and wings is presented. An unsteady parametric method to model the deforming motion is proposed and then implemented in a User-Defined Function (UDF). The UDF is used for driving dynamic mesh in ANSYS Fluent.
First, the framework is applied to a 2D airfoil equipped with a morphing Trailing-Edge Flap (TEF). A numerical validation of the steady and unsteady predictions is then performed against published data. Furthermore, the aerodynamic efficiency of the morphing concept is compared to an airfoil with a hinged TEF. It is found that an average of 6.5% increase in lift-to-drag ratio can be achieved with the morphed flap.
The framework is then used to study the flow response to a 2D downward flap deflection at various morphing frequencies. The slope of time histories of lift and drag coefficients were found to be proportional to the morphing frequency during the morphing phase. Contrary to the lift, however, the drag experiences an overshoot in its instantaneous values, resulting in efficiency loss for all frequencies before settling to a steady. This finding indicates the presence of unsteady effects that need to be taken into account during the design phase. Qualitative analysis reveals some similarities between rapid morphing and ramp-type pitching motion.
The framework is developed further to study continuous active flow control using a harmonically morphing TEF and its effect on the aerodynamic performance and acoustic spectra. The parametric method is modified to model the low amplitude (0.1 and 0.01% of the chord) harmonic morphing (combined upward and downward motion) in the TEF and the Ffowcs-Williams and Hawkings acoustic analogy was used for noise prediction. For this part of the work, a hybrid Reynolds-averaged Navier–Stokes–Large Eddy Simulation (RANS-LES) model, Stress-Blended Eddy Simulation (SBES), is used. It is shown that the 0.1% morphing amplitude induces higher sound pressure levels around the morphing frequency, and that all the morphing cases induce a shift in the main tone to a higher frequency, with a 1.5 dB reduction in the sound pressure levels. Apart from noise abatement, it is found that for a morphing frequency of 800 Hz and 0.01% amplitude it is possible to achieve up to 3% increase in aerodynamic efficiency.
Finally, a framework extension from 2D to 3D is proposed, by extending the parametrization method to model both the morphed TEF and the seamless flap side-edge transition between the morphing and static parts. A comparative study between a wing with a statically morphed flap and one with a hinged flap reveals that the morphed flap produces higher lift and lower drag resulting in an enhanced aerodynamic efficiency (CL/CD) of up to 40%. This enhanced efficiency is mainly due to the absence of gaps and the contribution of the seamless transition to lift generation. The unsteady analysis of the 3D dynamically morphed wing shows the presence of the drag overshoot, which is consistent with the 2D results. Finally, when comparing 2D and 3D CFD results, it is observed that 2D results tend to over-predict both the lift and drag. This is because 2D analysis assumes that the entire span is deflecting whereas the 3D wing would only have a portion of the flap deflecting.
The framework established in this thesis can be easily applied to other types of airfoils, leading-edge morphing, as well as wind and tidal turbine blades.

• Thesis Type: Thesis
• Publicly Available Date: Oct 14, 2019
• Keywords: CFD,Dynamic Mesh,Morphing,Wings,Aerospace,Airfoils,Aeroacoustics,Flow control,Aerodynamic,RANS,SBES,LES
• Public URL: https://uwe-repository.worktribe.com/output/1490739
• Award Date: Oct 14, 2019