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Title: Aeroelastic analysis of turbulent rotor flows
Author: Dehaeze, Florent
ISNI:       0000 0004 2737 0968
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2012
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This thesis is devoted to the study of rotor flows. A literature survey suggested that possible improvements can be achieved via better simulation of turbulence and prediction of the elastic blade de- formation. While the limits of the currently used URANS turbulence models have been shown, accurate predictions can only be achieved if the blade elasticity is taken account due to the large deformations a rotor blade can undergo in flight. An aeroelastic coupling strategy consists in three steps: computing the flow field, computing the structural deformation and transferring data between the CFD and CSD solvers. The transfer method also needs to deal with the different sizes for the structural and aerodynamic models. Most challenges come from the need to modify the CFD mesh following the blade deformation, and are linked to the higher refinement of the CFD grid. To tackle the problem, a new hybrid mesh deformation technique, adapted to rotor in-flight deformations was developed for the Helicopter Multi-Block solver of Liver- pool. Demonstration of the method was presented for multiple test cases: hovering HART-II rotors and forward flying ONERA 7A and HART-II rotors. The method proved quick at deforming the mesh and able to deal with large rotor deformations without downgrading the mesh quality. Another point of interest in this work was turbulence modelling. Aeroelastic calculations must capture the influence of the flow on the blade structure. Rotorcraft flows are complex, and due to the lim- its of the URANS models in predicting the frequency content in the flow, discrepancies in the structural forcing and the blade deformation might appear. Vibration levels might also see an improvement from a higher frequency content. The potential of DES models for rotorcraft flow was demonstrated using the stalled flow around a NACA002l wing as a test case. The frequency content obtained through DES was much wider and also allowed for better predictions of the mean flow field properties along with integrated loads. DES was applied to the HART-II rotor in order to assess the possible improvements coming from the use of DES. However, the difference between the URANS and the DES predictions of the flow field were limited, highlighting a grid or time step refinement need. A strong aeroelastic coupling strategy was also demonstrated, using the UH-60A rotor in high- speed forward flight. The key structural deformation was captured by the coupling strategy, and the dependency of the predictions to many flight and simulation parameters was highlighted.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral