Aerodynamic and Aeroacoustic Performance of Morphing Structures

Abstract

The aviation industry is one of the fastest growing industries, with the number of passengers expected to double over the next 20 years. This fast-paced commercial growth has generated a huge demand for highly efficient aircraft with improved aerodynamic and aeroacoustic performance. The aircraft wings are often designed for certain operating conditions, but the advent of morphing structures has enabled better design capabilities to expand their operating condition. In the present study, the aerodynamic and aeroacoustic behavior of morphing structures on two types of airfoils are investigated.

Firstly, experimental and numerical studies of a simple NACA 0012 airfoil fitted with two different flap profiles were successfully carried out to characterize their aerodynamic and aeroacoustic performance. The aerodynamic lift and drag measurements show improved lift-to-drag performance for the morphed flap airfoil compared to the hinged flap airfoil. The improved lift characteristics for the morphing flap airfoil was found to be due to the delayed flow separation observed in the surface flow visualization results. The flow measurement results showed that the downstream wake development can be significantly influenced by the trailing edge flap profile. Particle Image Velocimetry was used to study the flow over the flap and airfoil wake. The mean velocity contours within the airfoil wake region showed increased wake velocity deficit and turbulent kinetic energy for the morphed flap airfoil. The turbulent kinetic energy results displayed a characteristic double peak behavior, which was also the dominant content of the streamwise normal Reynolds shear stress component. Large eddy simulations were also carried out for the standard hinged and morphed airfoils and the results were validated with the experimental measurements. The unsteady flow characteristics were assessed in order to better understand the flow behavior around the morphed flap airfoil. The near-field and far-field acoustic results from the simulations showed that the morphed flap profile generates higher noise levels relative to hinged flap airfoil, which has been attributed to the increase level of surface pressure fluctuations at the trailing edge.

In the second phase of the project, the aerodynamic and aeroacoustic performance of an MDA 30P30N high-lift airfoil, fitted with slat cove fillers were examined experimentally. Measurements included lift and drag performance and mean surface pressure distribution, flow field analysis, near-field surface pressure fluctuations and far-field radiated noise. The flow measurement results show that there is no significant difference in the aerodynamic lift and drag between the standard 30P30N and that fitted with a slat cover filler. However, the slat cove filler configurations exhibit a much better lift-to-drag performance. The pressure coefficient results show that the use of slat cove fillers leads to a slight decrease in the suction peak over the main-element of the airfoil. In order to better understand the flow-field and the noise generation mechanism of the airfoil with slat cove fillers, simultaneous near-field and far-field noise measurements were carried out. The results showed that the use of the slat cove filler can generally lead to a significant reduction of the broadband noise and elimination of the tonal noise generated by the slat. The directivity pattern and the overall sound pressure level of the radiated noise have shown that a significant noise reduction can be achieved with the proper implementation of the slat cove fillers. The multiple tonal phenomena generated by the slat were also analyzed using the continuous wavelet transform method and higher order spectral analysis methods. The research carried out as part of this work has shown the great potential of morphing technologies for aerodynamically efficient and quiet airfoils and provides the impetus for further numerical and experimental work in this area.

Date of Award	7 May 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Mahdi Azarpeyvand (Supervisor) & Andres Marcos (Supervisor)