Unsteady aerodynamic effects in small-amplitude pitch oscillations of an airfoil

Abstract

High-fidelity wall-resolved large-eddy simulations (LES) are utilized to investigate the flow-physics of small-amplitude pitch oscillations of an airfoil at Re c = 100, 000. The investigation of the unsteady phenomenon is done in the context of natural laminar flow airfoils, which can display sensitive dependence of the aerodynamic forces on the angle of attack in certain "off-design" conditions. The dynamic range of the pitch oscillations is chosen to be in this sensitive region. Large variations of the transition point on the suction-side of the airfoil are observed throughout the pitch cycle resulting in a dynamically rich flow response. Changes in the stability characteristics of a leading-edge laminar separation bubble has a dominating influence on the boundary layer dynamics and causes an abrupt change in the transition location over the airfoil. The LES procedure is based on a relaxation-term which models the dissipation of the smallest unresolved scales. The validation of the procedure is provided for channel flows and for a stationary wing at Re c = 400, 000.

On the linear global stability analysis of rigid-body motion fluid–structure-interaction problems

“…The viscous terms are evaluated implicitly while extrapolation is used for the nonlinear terms. Over integration is used for a consistent evaluation of the nonlinear terms and a relaxation term based on the high-pass filtered velocity field is used to stabilize the method (Negi 2017). The stabilization method is based on the approximate deconvolution model with relaxation term (ADM-RT) method used for the large-eddy simulation of transitional flows (Schlatter, Stolz & Kleiser 2004, 2006 and has been validated with channel flows and flow over wings in Negi et al (2018).…”

Aerodynamic Effects of Uniform Blowing and Suction on a NACA4412 Airfoil

“…We designed the mesh considering the results of the validation of the SGS model performed by Negi et al (2018), who compared DNS and LES results from a simulation of a NACA4412 airfoil at Re c = 400,000 , showing very good agreement between both. Following the same guideline, the grid spacing in the turbulent-boundary-layer region in the proximity of the airfoil surface is x + t = 18 , y + n = (0.64, 11) and z + = 9 respectively in the wall-normal, wall-tangential and spanwise directions.…”

Effect of adverse pressure gradients on turbulent wing boundary layers

“…validated by Negi et al (2018) against the fully resolved DNS data of the NACA4412 wing section at Re c = 400 000 by Hosseini et al (2016). In this study approximately 90 % of the total dissipation of turbulent kinetic energy (TKE) is resolved by the LES while the remaining 10 % is added by the SGS model.…”