Digital-filter and forward-stepwise method-based synthetic inflow turbulence generation: applications to horizontal axis turbines

Abstract

The main aim of this study is to create an easy-to-reproduce knowledge unit wherein the digital-filter method-based (DFM) and forward-stepwise method-based (FSM) synthetic inflow generator classes are conceptualised, explored, and improved for large eddy simulation applications (LES). To this end, the following novelties were introduced: [i] both classes were abstracted and documented into four non-CFD and five CFD model stages, [ii] two new DFM variants were derived, [iii] with these two, four preexisting DFM-FSM variants were code implemented, [iv] a new analytic function that can transform the skewness-kurtosis of synthetic inflow to target values without changing existing statistics was derived and verified, [v] two other skewness-kurtosis transformation approaches were derived and proved ineffectual, [vi] five easy-to-code computational speedup techniques for DFM-FSM were introduced and quantified, [vii] two new methods to enable DFM-FSM to be computed on nonuniformly-discretized arbitrary boundary geometries were developed, [viii] a preliminary method to ensure the divergence freeness in DFM-FSM was studied, [ix] each DFM-FSM model stage was evaluated by controlled studies of extensive-than-the-literature range of input variables and output statistics within non-CFD and LES environments through decaying homogeneous isotropic turbulence, homogeneous shear turbulence and smooth-wall plane channel flow, [x] five LES post-solution verification approaches were reviewed and compared via these building-block flows. In addition, horizontal axis wind and marine turbine flows were explored by various means including DFM-FSM: [xi] for these explorations, in-house codes were written and verified for the blade element momentum theory (BEMT), the time-accurate Euler-Bernoulli beam theory, a BEMT-CFD coupling through the actuator disk method, and the actuator line method, [xii] hydrodynamics of a marine turbine under decaying homogeneous isotropic turbulence with four different turbulence intensities were investigated by wall-modelled & actuator-line modelled LES computations, and twelve analytical wake models, [xiii] the arbitrary mesh interface technique under turbulent inflows was quantitatively assessed, and lastly, [xiv] considerable amount of for-the-first-time observations and remarks were quantified and reported.

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ORCID for Zhengtong Xie: orcid.org/0000-0002-8119-7532

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