Multiscale modal analysis of an oscillating impinging gas jet

• Published in: Experimental thermal and fluid science Vol. 91; pp. 256 - 276
• Main Authors: Mendez, M.A., Scelzo, M.T., Buchlin, J.-M.
• Format: Journal Article
• Language: English
• Published: Philadelphia Elsevier Inc 01.02.2018; Elsevier Science Ltd
• Subjects: Configurations; Confinement; Cooling; Correlation analysis; Coupled modes; Decomposition; Deformation mechanisms; Dynamic masks for TR-PIV; Feedback; Flow visualization; Fluid dynamics; Fluid flow; Fluid mechanics; Formability; Frequency analysis; Frequency dependence; Gas jets; Heat transfer; Image processing; Incompressible flow; Interfaces; Jet flow; Modal analysis; Multiresolution analysis; Multiscale analysis; Multiscale modal analysis; Nozzles; Particle image velocimetry; Proper Orthogonal Decomposition; Proper Orthogonal Decomposition (POD); Self-sustained oscillations of jet flows; Stagnation point; Time-frequency analysis; Velocity measurement; Wavelet analysis; Self-sustained oscillations of jet flows; Multiscale modal analysis; Dynamic masks for TR-PIV; Proper Orthogonal Decomposition (POD)
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2017.10.032

•A 2D oscillating jet impinging on a pulsing interface is characterized experimentally.•Algorithms for detecting jet flow and interface in HSV/TR-PIV videos are presented.•Continuous Wavelet Transform is used for time–frequency analysis of the oscillation.•TR-PIV fields are processed with a new data-driven decomposition referred to as mPOD.•The mPOD reveals a large scale and a fine scale response of the jet flow. Oscillating impinging gas jets are encountered in many flow configurations, including fluidic devices, jet flow discharges into cavities and jet impinging onto deformable interfaces. For an incompressible flow, the self-sustained mechanism is referred to as hydrodynamic feedback and it is linked to the interaction between the flow field and its geometric confinement. This work presents an experimental characterization of the flow structures responsible for the hydrodynamic feedback, considering both a steady confinement and a pulsing confinement. The selected configuration consists of a planar gas jet impinging on an asymmetric interface consisting of a flat wall on one side of the stagnation region and bidimensional bump on the other. This bump is fixed in the steady condition and pulses in the unsteady conditions. Jet oscillation and interface tracking are carried out by means of high-speed flow visualization and image processing, combined with a time-frequency analysis in the Fourier and Wavelet spaces. The flow field is characterized via Time-Resolved Particle Image Velocimetry (TR-PIV) and analyzed with a novel modal decomposition, referred to as multi-scale Proper Orthogonal Decomposition (mPOD). This decomposition uses multiresolution analysis (MRA) on the correlation matrix to produce a set of PODs at multiple scales. Two physical mechanisms of the hydrodynamic feedback have been captured at largely different scales and the dynamic of their characteristic flow structures is presented. The first, referred to as fluidic mode, consists of a self-sustained oscillation of the impinging jet; the second, referred to as coupled mode, consists of a periodic downward deflection of the impinging jet, at the frequency of the interface pulsation.