Analysis of turbulent coherent structures in large eddy simulations of dynamic stall

Abstract

The current proposal describes the research plan associated to the overseas internship (BEPE) of student Brener D'Lélis Oliveira Ramos. The student is currently enrolled in the Graduate Program of Mechanical Engineering at University of Campinas, UNICAMP, and he is funded by a FAPESP MSc Scholarship, Process No. 2016/24504-6. The internship period abroad should be held at Florida State University, FSU, located in Tallahassee, FL, USA. During this period, Brener will work under the supervision of Prof. Kunihiko Taira who is currently an Associate Professor in the Department of Mechanical Engineering at FSU. Prof. Taira has extensive expertise in the fields of flow modal decomposition, analysis of coherent structures, reduced order modeling, flow control, computational fluid dynamics and numerical methods. All these topics are related to the present research proposal.This project aims to study airfoils in dynamic stall. This phenomenon often occurs on rotors of helicopters at high forward flight speeds or during maneuver and it is responsible for large torsional airloads and vibrations on the rotor blades. Hence, it is a limiting factor for the helicopter performance. Furthermore, dynamic stall also finds application in the study of micro air vehicles which mimic natural fliers and wind turbines. Here, we will combine compressible large eddy simulations with methods of flow modal decomposition for the identification of turbulent coherent structures which are energetically and dynamically relevant for the flow physics of dynamic stall. Techniques such as (spectral) proper orthogonal decomposition, (S)POD, dynamic mode decomposition, DMD, Lagrangian coherent structures, resolvent analysis and wavelet transforms may provide information on coherent structures and flow instabilities that are not clearly observed in numerical simulations of turbulent flows. In this work, we will apply the most pertinent techniques for unsteady flow problems involving dynamic stall. It is important to mention that the research group at FSU is advancing the application of such tools in the context of turbulent flows and LES. The results obtained in the current collaboration will provide relevant information for the development and application of control techniques for improving the flight performance in flow configurations involving dynamic stall. (AU)