Numerical investigation of woven wire mesh screens for landing gear aerodynamic flow and noise control
Citation:
OKOLO, PATRICK NWOSA, Numerical investigation of woven wire mesh screens for landing gear aerodynamic flow and noise control, Trinity College Dublin.School of Engineering.MECHANICAL AND MANUFACTURING ENGINEERING, 2018Download Item:
Abstract:
Recently, acoustic engineers, researchers, and relevant institutions seek to reduce noise levels associated with the aerodynamic complexities of an aircraft, particularly within close proximity to airport communities. The environmental and health effects caused by aircraft noise emission has increased the level of research in this area, with new policies aiming to address such negatives and to reduce noise levels associated with an aircraft.
Aircraft landing gear contributes a major percentage to the overall noise emitted from an aircraft on approach to landing. Significant improvements have been made to the aero-engine which now position airframe noise, and landing gear noise in particular, as the threshold below which no further noise reduction can be made without addressing these now important noise sources. This current research is a numerical investigation on the use of woven wire mesh screens as fluid flow control mediums and for landing gear noise control.
The introductory part of this thesis presents the motivation behind this research. Whilst improvements in processor speeds and the introduction of new and needed computational approaches such as the Lattice-Boltzman Method have allowed fairings and perforated plates, which serve as low noise landing gear technologies to be fully resolved and examined numerically, a full-scale solution for a wire mesh screen with its very small length scales is still a significant computational challenge. Therefore, there is a need for an alternative, faster, yet sufficiently accurate method of simulating such screens numerically for aerodynamic noise studies. An alternative method is hereby proposed and is implemented using the Volume-Averaged Method within a porous zone of interest in the numerical fluid domain, in which are added the characteristics of realistic woven wire mesh screens. To date in the literature, wire mesh screens have not been studied using the Volume Averaged Method and where the VAM has been used for coarser studies, such as for perforated plates, only the impact of a pressure drop was implemented. In this thesis important additional consequences of the inclusion of a wire mesh screen, with its very fine and complex gap geometries, are also added to the VAM, such as turbulence suppression, so that the model might be enhanced and more accurately capture the true physics of the fluid/screen interactions.
Chapter \ref{lit} presents a literature review of aerodynamic noise generation, landing gear noise sources, noise reduction techniques applied to date, principles of computational aeroacoustics, computational modeling of perforated surfaces and wire mesh screens, and semi-empirical noise prediction models of aircraft airframe. Contributions of the thesis are also highlighted, particularly the potential benefits and applications.
So that a better understanding of turbulent fluid flow properties might be obtained around and downstream of a wire screen mesh, Chapter 3 examines, in 3-D, a fully resolved wire mesh screen and is compared to classic benchmark results published by NACA. This allows the parameters such as Flow Loss Coefficients and Turbulence Decay to be studied as a function of porosity and distance downstream. Results compare well with each other and with the near-field empirical correlation of turbulence decay of Roach \cite{roach_generation_1987}.
Chapter 4 presents a resolved 2-D realistic representation of the 3-D wire screen mesh from chapter 3 in order to examine the flow field at further downstream distances. These results compare well with both the 3-D numerical model and the NACA study.
With this detailed understanding of the effect wire mesh screens may have on the fluid mechanics of flows downstream, Chapter 5 employs the Volume Averaged Method at full scale for a wire mesh screen as a low noise technology applied to an H-Strut test case. The VAM is enhanced with the inclusion of the turbulence suppression term and is compared to the experimental flow field and acoustic results of the EU TIMPAN (Technologies to Improve Airframe Noise) project. For this large-scale study, results from this modeled method, as opposed to a resolved approach, are good, much faster and are demonstrated to be greatly improved with the addition of the turbulence effects which hitherto had been neglected.
Chapter 6 extends the evaluation of the VAM method to a comparison with half scale main landing gear EU project results: ALLEGRA. The comparison is rudimentary but demonstrates the potential for future work.
Sponsor
Grant Number
Clean Sky Joint Technology Initiative under grant agreements number [308225] (ALLEGRA) and number [620188] (ARTIC)
Author's Homepage:
http://people.tcd.ie/okolopDescription:
APPROVED
Author: OKOLO, PATRICK NWOSA
Advisor:
Bennett, GarethPublisher:
Trinity College Dublin. School of Engineering. Discipline of Mechanical & Manuf. EngType of material:
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