Computational aeroelastic analysis of slowed rotors at high advance ratios

Abstract

The aerodynamic and aeroelastic behaviour of a rotor become more complex as advance ratios increase to achieve high-speed forward fight. As the rotor blades encounter large regions of cross and reverse flows during each revolution, strong variations in the local Mach regime are encountered, inducing complex elastic blade deformations. In addition, the wake system may remain in the vicinity of the rotor, adding complexity to the blade loading. The aeroelastic behaviour of a model rotor with advance ratios ranging from 0·5 to 2·0 has been evaluated with aerodynamics provided via a computational fluid dynamics (CFD) method. Significant radial blade-vortex interaction can occur at a high advance ratio; the advance ratio at which this occurs is dependent on the rotor configuration. This condition is accompanied by high vibratory loads, peak negative torsion, and peak torsion and in-plane loads. The high vibratory loading increases the sensitivity of the trim model, so that at some high advance ratios the vibratory loads must be filtered to achieve a trimmed state.

Unstructured overset incompressible computational fluid dynamics for unsteady wind turbine simulations

“…This practice works well for most configurations, although some issues have been encountered with configurations with very highly separated flows near the edge of the operating envelope. Thrust, defined here as force directed along the rotor axis that is averaged over a revolution, is not normally a quantity of interest for wind turbines but is less difficult to predict with CFD than torque, which can have difficulties with the integration of forces at the blade tips . To facilitate more accurate comparisons between measured data and computational data, thrust was integrated using the same method described in the NREL Phase VI test report .…”

Physics and Modeling of Large Flow Disturbances: Discrete Gust Encounters for Modern Air Vehicles

“…Flow coupling is also a major concern for vortex gusts, where the influence of the wing on the upstream flow can be significant (Figure 7b). In rotary-wing applications, for example, the alignment of a shed vortex with its eventual collision point has a large influence on the blade response, even for small disturbances (De Montaudouin et al 2014). In a 2D flow where the core of the vortex is aligned with the leading edge of the wing, even inviscid models show the influence of the presence of the wing on the trajectory of the vortex.…”

“…Except for the parallel vortex, these encounters are an inherently 3D problem, as vortex alignment and rotation govern the type of instability that arises and affects unsteady wing loading (Barnes et al 2016). For example, BVIs result in vibratory loading, which can be significantly increased when the vortex orientation is situated along the rotor radius at high ratios of forward flight to rotor tip speed (De Montaudouin et al 2014, Yeo 2013, resulting in unacceptable flight conditions. Larger-amplitude BVIs can result in separated flows and dynamic stall on the rotor.…”