Three-dimensional behavior of low-frequency unsteadiness in the incompressible turbulent separation bubble (TSB) produced by a wall-mounted hump is investigated using time-resolved planar and stereoscopic particle image velocimetry measurements at several planes across the separated region. The aspect ratio (wind tunnel width/separation length, ) provides nominally two-dimensional flow for more than half of the spanwise extent of the test section. Analysis in the streamwise/wall-normal plane along the center of the test section shows low-frequency () large-scale motion of the separated region. The flowfield contains features of both geometry-induced and pressure-gradient-induced separation, but unsteady dynamics produce dominant frequencies closer to geometry-induced TSBs () compared to purely pressure-gradient-induced TSBs (). Measurements along the spanwise direction and parallel to the initial shear layer development show strong evidence that the low-frequency motion is inherently three-dimensional, providing an additional dimension to the understanding of the flapping/breathing typically observed in planar streamwise/wall-normal measurements. Spectral proper orthogonal decomposition and low-order modeling identify spanwise undulations with wavelengths of the order of and frequencies of . The three-dimensional behavior causes a peak/valley formation along the span and a more localized expansion/contraction, leading to only small variations in the integral volume of the TSB.
Three-Dimensional Nature of Low-Frequency Unsteadiness in a Turbulent Separation Bubble
AIAA Journal ; 62 , 11 ; 4349-4363
2024-11-01
Article (Journal)
Electronic Resource
English
Spanwise Aspects of Unsteadiness in a Pressure-Induced Turbulent Separation Bubble (AIAA 2018-3538)
British Library Conference Proceedings | 2018
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