09:40
Flow induced vibrations
Chair: Luca Benassi
09:40
30 mins
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Flow-induced vibration of a pitch-plunge aeroelastic system subjected to external vortical disturbances
Chandan Bose, Grigorios Dimitriadis
Abstract: The characterization of nonlinear aeroelastic instabilities under undisturbed freestream conditions has been the subject of continued interest in the existing literature. However, the effect of upstream flow disturbances on the dynamic behaviour of aeroelastic systems has remained relatively unexplored. Recent studies have mostly considered the temporal fluctuation of the inflow and reported that the aeroelastic response dynamics strongly depends on the inflow conditions [1]. In practice, aeroelastic systems are often subjected to spatio-temporal flow disturbances; one such situation is when an aeroelastic system encounters a vortical wake [2]. This abstract proposes to systematically investigate the influence of a vortical wake coming from an upstream bluff-body on the response dynamics of a canonical pitch-plunge aeroelastic system.
To this end, the flow-induced vibration of a two degrees-of-freedom (2-DoF) airfoil section in the wake of an upstream bluff body is simulated using the open-source library OpenFOAM. The present fluid-structure interaction framework is developed by coupling a Navier-Stokes solver with the structural model using a partitioned weak coupling approach. The unsteady flow-field is simulated at a Reynolds number of 2 × 10^4 using the incompressible Navier-Stokes solver - overPimpleDyMFoam. The structural counterpart comprises a stationary bluff body situated upstream of the 2-DoF pitch-plunge aeroelastic system. The elastically-mounted airfoil motion is simulated using the six-degrees-of-freedom rigid body motion solver available in OpenFOAM. The Newmark time-integration scheme is used to solve the structural equations.
The oscillation amplitude of an aeroelastic system, situated in the primary wake formation region of an upstream bluff-body, can attain a considerably high value if the coupled system frequency locks in with the shedding frequency of the bluff-body, thus offering significant potential for energy extraction. The primary focus is to study the effect of the oscillating velocity field due to periodic vortex shedding behind the upstream bluff body on the flutter characteristics of the aeroelastic system and the underlying wake-structure interactions. The findings of this study can benefit the efficient design of biologically inspired propulsion systems and energy harvesters.
References:
1. Dominique C Poirel and Stuart J Price. Structurally nonlinear fluttering airfoil in turbulent
flow. AIAA Journal, 39(10):1960–1968, 2001.
2. Zachary N Gianikos, Benjamin A Kirschmeier, Ashok Gopalarathnam, and Matthew Bryant. Limit cycle characterization of an aeroelastic wing in a bluff body wake. Journal of Fluids and Structures, 95:102986, 2020.
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10:10
30 mins
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Investigation of vortex-induced vibrations to compare Reynolds-averaged Navier-Stokes and detached-eddy simulations
Kilian Streitenberger, Jens Nitzsche
Abstract: The increasing power of high-performance computing leads to a more efficient use of scale resolving CFD. The effects of these methods on the aeroelastic behaviour are not known well yet. The Aim is to analyse an aeroelastic test case for scale-resolved numerical flow simulation. Several two-dimensional Reynolds-averaged Navier-Stokes (RANS) and three-dimensional delayed-detached-eddy simulations (DDES) are performed with the NACA0021 airfoil at high angles of attack (AoA) of 60° and 70° at Mach 0.1 and a Reynolds number of 2.7×〖10〗^5 to investigate vortex-induced vibration (ViV). The focus is on the difference between RANS and scale-resolving methods and the analysis of the turbulence in the wake behind the wing. A rigid body test case is used as a basis. The flow behind NACA0021 shows a strong vortex system in the wake with a dominant frequency for this rigid body case. Fluid-Structure Interaction (FSI) and forced motion simulations are performed on this basis. A grid study for the RANS- and DDES-simulation was performed for for the rigid airfoil at 60° AoA. At 70° AoA, both simulation methods show a strong lock-in behaviour with a large influence on the turbulent kinetic energy in the resolved wake turbulence. Without lock-in, this energy is about ten times higher than with lock-in. The correlation of the x-velocity in the turbulent wake over the span is also investigated. Outside the lock-in region, there is no effect of motion on the span correlation. Inside the lock-in region, the correlation increases significantly in the spanwise direction. Compared to the RANS simulation, the frequency range of the lock-in is slightly smaller for DDES. The vortex-induced vibration's maximum amplitude is almost the same in both simulations. In the rigid case, there is a significant difference between RANS and DES in terms of integral forces. This difference decreases significantly when the profile is set in motion. Remarkedly there is no significant difference between RANS and DES in terms of the integral forces and the ViV amplitude and frequency on the oscillating airfoil under lock-in conditions.
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