基于空间尺度的流动分解（英文）

【作者】 任杰； 毛雪瑞； 符松；

【机构】 Department of Mechanical Engineering,Faculty of Engineering,University of Nottingham； 清华大学航天航空学院；

【摘要】 We propose an image-based flow decomposition developed from the two-dimensional(2 D) tensor empirical wavelet transform(EWT)(Gilles 2013).The idea is to decompose the instantaneous flow data,or its visualisation,adaptively according to the averaged Fourier supports for the identification of spatially localised structures.The resulting EWT modes stand for the decomposed flows,and each accounts for part of the spectrum,illustrating fluid physics with different scales superimposed in the original flow.With the proposed method,decomposition of an instantaneous 3 D flow becomes feasible without resorting to its time series.Examples first focus on the interaction between a jet plume and 2 D wake,where only experimental visualisations are available.The proposed method is capable of separating the jet/wake flows and their instabilities.Then the decomposition is applied to an early stage boundary layer transition,where direct numerical simulations provided a full data-set.The tested inputs are the 3 D flow data and its visualisation using streamwise velocity & λ2 vortex identification criterion.With both types of inputs,EWT modes robustly extract the streamwise-elongated streaks,multiple secondary instabilities and helical vortex filaments.Results from 2 D stability analysis justify the EWT modes that represent the streak instabilities.In contrast to POD or DMD that extract spatial modes according to energy or frequency,EWT provides a new strategy as to decompose an instantaneous flow from its spatial scales.更多还原

【Abstract】 We propose an image-based flow decomposition developed from the two-dimensional(2 D) tensor empirical wavelet transform(EWT)(Gilles 2013).The idea is to decompose the instantaneous flow data,or its visualisation,adaptively according to the averaged Fourier supports for the identification of spatially localised structures.The resulting EWT modes stand for the decomposed flows,and each accounts for part of the spectrum,illustrating fluid physics with different scales superimposed in the original flow.With the proposed method,decomposition of an instantaneous 3 D flow becomes feasible without resorting to its time series.Examples first focus on the interaction between a jet plume and 2 D wake,where only experimental visualisations are available.The proposed method is capable of separating the jet/wake flows and their instabilities.Then the decomposition is applied to an early stage boundary layer transition,where direct numerical simulations provided a full data-set.The tested inputs are the 3 D flow data and its visualisation using streamwise velocity & λ2 vortex identification criterion.With both types of inputs,EWT modes robustly extract the streamwise-elongated streaks,multiple secondary instabilities and helical vortex filaments.Results from 2 D stability analysis justify the EWT modes that represent the streak instabilities.In contrast to POD or DMD that extract spatial modes according to energy or frequency,EWT provides a new strategy as to decompose an instantaneous flow from its spatial scales.更多还原