Shear Layer of Inclined Jets in Crossflow Studied with Spectral Proper Orthogonal Decomposition and Spectral Transfer Entropy

Several classes of vortical structures are present in a jet in crossflow, and the present paper sets out to investigate one of them: jet shear layer unsteadiness. An inclined jet in crossflow that is relevant to discrete hole film cooling applications is considered, with focus on two velocity ratios, r = 1 and r = 2. Highly resolved large eddy simulations (LES) described and validated in previous work are employed. Power spectra show that shear layer oscillations contain a broader range of frequencies than suggested by previous studies, and two spectral techniques are used to investigate this behavior. Spectral proper orthogonal decomposition (SPOD) shows modes that encompass the hole and the shear layer, suggesting their motions are linked. Then, we develop and employ a technique to establish causality between signals in different locations called spectral transfer entropy (STE), which is adapted from information theory. The results show that unsteadiness in the hole affects the spectral content of the shear layer, confirming the importance of resolving the plenum and the hole in simulations with realistic jet inflow, such as film cooling configurations. (C) 2019 Elsevier Ltd. All rights reserved.