Optimised hybrid parallelisation of a CFD code on Many Core architectures

COSA is a novel CFD system based on the compressible Navier-Stokes model for unsteady aerodynamics and aeroelasticity of fixed structures, rotary wings and turbomachinery blades. It includes a steady, time domain, and harmonic balance flow solver. COSA has primarily been parallelised using MPI, but there is also a hybrid parallelisation that adds OpenMP functionality to the MPI parallelisation to enable larger number of cores to be utilised for a given simulation as the MPI parallelisation is limited to the number of geometric partitions (or blocks) in the simulation, or to exploit multi-threaded hardware where appropriate. This paper outlines the work undertaken to optimise these two parallelisation strategies, improving the efficiency of both and therefore reducing the computational time required to compute simulations. We also analyse the power consumption of the code on a range of leading HPC systems to further understand the performance of the code.Comment: Submitted to the SC13 conference, 10 pages with 8 figure

Robust aerodynamic design optimization of variable speed wind turbine rotors

Background: Manufacturing and assembly tolerances may cause wind turbine (WT) energy production to differ significantly from nominal design targets. Issue can be alleviated in two ways: A. Reducing tolerances. This may be expensive. B. Developing reliable and computationally affordable robust analysis and design optimization technologies. Robust WT rotor is one yielding minimal variations of aerodynamic performance arising due to errors affecting rotor geometry. Objectives: To develop/demonstrate computational framework for the robust design optimization of WT rotors. Main aim is to 1) maximize expectation and 2) minimize standard deviation of yearly energy production. Highlight computational effectiveness of the Univariate Reduced Quadrature approach to ‘deterministic’ uncertainty propagation. Highlight capabilities of a recently developed multi-level evolution-based optimizer

Probabilistic analysis of wind turbine performance degradation due to blade erosion accounting for uncertainty of damage geometry

Geometry alterations of wind turbine blades due to erosion reduce the blade aerodynamic performance, yielding turbine power and energy losses. This study proposes a novel probabilistic analysis framework combining computational fluid dynamics, probabilistic and deterministic uncertainty propagation, and high-performance computing to assess this performance degradation accounting for the unavoidable uncertainty on field records of blade erosion. This uncertainty presently prevents using erosion records for improving wind turbine maintenance planning, increasing energy yield, and thus further reducing the wind energy cost. The technology is demonstrated by quantifying the statistical moments of power and energy yield losses of an eroded utility-scale turbine at a North Sea offshore site and a southern European onshore site. The expectations of the offshore and onshore annual energy production losses are found to be 2 and 3% of the corresponding nominal values, respectively, with corresponding standard deviations of 0.1 and 0.15%. In the realistic scenario of erosion varying with high radial frequency, these low standard deviations result from partial compensation of the impact of mild and severe damages. These low standard deviations indicate that present uncertainty levels of erosion geometry records can be handled with uncertainty analysis in predictive maintenance for further reducing wind energy costs. With the frequent assumption of small or no radial variation of erosion, the standard deviation of the loss is misleadingly higher. For the first time, the study reports on the significant impact of turbulence intensity of the installation site on the turbine loss variability with the site wind characteristics

Harmonic balance Navier-Stokes analysis of tidal stream turbine wave loads

ARCTIC, a novel incompressible Reynolds–averaged Navier–Stokes finite volume code for the hydrodynamic analysis of open rotor unsteady loads is presented. One of its unique features is a harmonic balance solver enabling high–fidelity analyses of turbine periodic hydrodynamic loads with runtimes reduced by more than one order of magnitude over conventional time–domain CFD, and with negligible accuracy penalty. The strength of the new technology is demonstrated by analyzing with both harmonic balance and time–domain solvers the load fluctuations of a realistic tidal stream turbine. Such fluctuations are caused by a harmonic perturbation of the freestream velocity similar to that due to surface gravity waves

Cross-comparative analysis of loads and power of pitching floating offshore wind turbine rotors using frequency-domain Navier-Stokes CFD and blade element momentum theory

Reliable predictions of the aero- and hydrodynamic loads acting on floating offshore wind turbines are paramount for assessing fatigue life, designing load and power control systems, and ensuring the overall system stability at all operating conditions. However, significant uncertainty affecting both predictions still exists. This study presents a cross-comparative analysis of the predictions of the aerodynamic loads and power of floating wind turbine rotors using a validated frequency-domain Navier-Stokes Computational Fluid Dynamics solver, and a state-of-the-art Blade Element Momentum theory code. The considered test case is the National Renewable Energy Laboratory 5 MW turbine, assumed to be mounted on a semi-submersible platform. The rotor load and power response at different pitching regimes is assessed and compared using both the high- and low-fidelity methods. The overall qualitative agreement of the two prediction sets is found to be excellent in all cases. At a quantitative level, the high- and low-fidelity predictions of both the mean rotor thrust and the blade out-of-plane bending moments differ by about 1 percent, whereas those of the mean rotor power differ by about 6 percent. Part of these differences at high pitching amplitude appear to depend on differences in dynamic stall predictions of the approaches

Feasibility of the Navier-Stokes harmonic balance method for modelling aircraft unsteady aerodynamics

Traditionally, the models of the unsteady aerodynamic loads needed for aircraft flight simulations have been estimated using the aerodynamic derivatives approach, which, using linear aerodynamic models, provides the influence of the aircraft motion rates on the aerodynamic forces and moments. With increasing aircraft maneuverability resulting in nonlinear unsteady flow regimes, however, the linearity assumption of the conventional aerodynamic derivatives approach makes the method questionable. Methods with higher reliability have been show to be achievable by using knowledge of the aircraft aerodynamic response to harmonic excitations. Prompted by the need of rapidly and accurately estimating such response, this study demonstrates the applicability of the nonlinear frequency-domain Navier-Stokes Harmonic Balance method for predicting periodic aircraft flows with low and high levels of nonlinearity. Using the NASA Common Research Model aircraft case study, it is found that the Harmonic Balance technology yields estimates of the unsteady forces differing negligibly from those of the standard time-domain Navier-Stokes method with a runtime analysis reduced by at least one order of magnitude over that of the time-domain approach. © 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018. All rights reserved

Load balance and Parallel I/O: Optimising COSA for large simulations

This paper presents the optimisation of the parallel functionalities of the Navier-Stokes Computational Fluid Dynamics research code COSA, a finite volume structured multi-block code featuring a steady solver, a general purpose time-domain solver, and a frequency-domain harmonic balance solver for the rapid solution of unsteady periodic flows. The optimisation focuses on improving the scalability of the parallel input/output functionalities of the code and developing an effective and user-friendly load balancing approach. Both features are paramount for using COSA efficiently for large-scale production simulations using tens of thousands of computational cores. The efficiency enhancements resulting from optimising the parallel I/O functionality and addressing load balance issues has provided up to a 4x performance improvement for unbalanced simulations, and 2x performance improvements for balanced simulations

Impact of meteorological data factors and material characterization method on the predictions of leading edge erosion of wind turbine blades

Leading edge erosion of wind turbine blades is a major contributor to wind farm energy yield losses and maintenance costs. Presented is a multidisciplinary framework for predicting rain erosion lifetimes of wind turbine blades. Key aim is assessing the sensitivity of lifetime predictions to: modeling aspects (material erosion model, blade aerodynamics), input data and/or their preprocessing (joint frequency distribution of wind speed and droplet size based on synchronous site-specific measurements versus frequency distribution generated with partly site-agnostic modeling standards, wind speed records of nacelle anemometer or extrapolated at hub height from met masts), and environmental conditions (UV weathering). The analyses consider a Northwest England onshore site where a utility-scale turbine is operational, focus on a reference 5 MW turbine assumed operational at the site, and use a typical leading edge coating material. It is found that the largest variations in erosion lifetime predictions are due to material erosion model (based on rain erosion test data or fundamental material properties) and wind and rain model (measurement-based joint wind speed and droplet size distribution or standard-based modeled distribution). The use of joint wind and rain distribution also enables identifying wind/rain states with highest erosion potential, knowledge paramount to deploying erosion-safe turbine control

Compressible Navier-Stokes analysis of floating wind turbine rotor aerodynamics

The unsteady aerodynamics of floating offshore wind turbine rotors is more complex than that of fixed-bottom turbine rotors, due to additional rigid-body motion components enabled by the lack of rigid foundations; it is still unclear if low-fidelity aerodynamic models, such as the blade element momentum theory, provide sufficiently reliable input for floating turbine design requiring load data for a wide range of operating conditions. High-fidelity Navies-Stokes CFD has the potential to improve the understanding of FOWT rotor aerodynamics, and support the improvement of lower-fidelity aerodynamic analysis models. To accomplish these aims, this study uses an in-house compressible Navier-Stokes code and the NREL FAST engineering code to analyze the unsteady flow regime of the NREL 5 MW rotor pitching with amplitude of 4o and frequency of 0.2 Hz, and compares all results to those obtained with a commercial incompressible code and FAST in a previous independent study. The level of agreement of CFD and engineering analyses in each of these two studies is found to be quantitatively similar, but the peak rotor power of the compressible flow analysis is about 20 % higher than that of the incompressible analysis. This is possibly due to compressibility effects, as the instantaneous local Mach number is found to be higher than 0.4. Validation of the compressible flow analysis set-up, using an absolute frame formulation and low-speed preconditioning, is based on the analysis of the steady and yawed flow past the NREL Phase VI rotor