Turbulent wake interaction LES and aeroacoustic predictions [electronic resource]

As increased scrutiny and regulation is placed on the environmental impact of air transportation, tools and methods which enable design of lower footprint next generation aircraft become critical. One of the major environmental obstacles to air travel is noise impact on communities during departure and arrival. Jet noise, dominant during take off, has been studied extensively and as the field has matured, attention has turned to airframe noise - a significant fraction of the total noise signature during approach to landing. As a result, the development of accurate prediction tools for noise generated by complex airframe systems is necessary. Since direct simulation of aerodynamic noise, particularly when realistic geometries and Reynolds numbers are considered, is prohibitively expensive, hybrid methods have become the de-facto standard. In such methods, the near flow field is computed by a given Computational Fluid Dynamics (CFD) simulation while the far-field noise is predicted by a separate acoustic analogy. In this dissertation, we first demonstrate the advantages and challenges of Large Eddy Simulation for the prediction of the near flow field using a simple tandem cylinder geometry. This configuration has been identified by the computational aeroacoustic (CAA) community as a benchmark problem, representative of airframe components such as landing gear struts and hydraulic lines. Since realistic engineering problems typically occur in high Reynolds number flow regimes, forced transition trips are often employed in experiments which are used as benchmarks for simulation results. This was the case in the tandem cylinder problem, and it was found that a naively applied numerical transition trip resulted in significant extraneous noise generation. In the second part of this work, we develop an improved numerical trip which reduces the acoustic impact on the far field. The bulk of this work concentrates on the prediction of noise generated by a model airfoil-cylinder interaction problem. The objective of this portion is twofold: first, common industry practice in the noise prediction of complicated geometries is to exclude the effect of volume noise source terms ("quadrupole sources") due to the prohibitive cost of including them. This is based on the commonly held assumption that their effect is minimal compared to that of surface fluctuation source terms ("dipole sources") in low Mach number conditions. The goal here is to determine if this is still a valid assumption when turbulent flow interaction between two or more bodies is present. Additionally, if volume sources are necessary for accurate prediction, our goal is to examine when they may be important to include (based on Mach number and variation in geometry) and what the volume sources physically represent. The second objective is to compare the results of three separate acoustic prediction methods to explore possible generation of erroneous numerical noise when using common porous-surface Ffowcs Williams & Hawkings (FWH) integration predictions.

Keywords: Aeronautics and Astronautics.
Advisor: Lele Sanjiva K. (Sanjiva Keshava)
Alonso Juan José
Moin Parviz advisor. Thesis advisor