Three dimensional structure of the unsteady wake of an axisymmetric body
| Autor: | Martin A. Passmore, Mathew T. Almond, Max Varney, Giancarlo Pavia |
|---|---|
| Rok vydání: | 2019 |
| Předmět: |
Fluid Flow and Transfer Processes
Physics Plane (geometry) Mechanical Engineering Computational Mechanics Rotational symmetry Reynolds number Geometry Wake Condensed Matter Physics 01 natural sciences 010305 fluids & plasmas Vortex Physics::Fluid Dynamics symbols.namesake Reflection symmetry Particle image velocimetry Mechanics of Materials 0103 physical sciences symbols 010306 general physics Axial symmetry |
| Zdroj: | Physics of Fluids. 31:025113 |
| ISSN: | 1089-7666 1070-6631 |
| DOI: | 10.1063/1.5078379 |
| Popis: | The near-wake of an axisymmetric body has been investigated using base pressure tappings and large scale Tomographic Particle Image Velocimetry (TPIV) at a Reynolds number of ReD = 3.2 × 105, based upon model diameter. Insights into the near-wake dynamics are provided by the application of Proper Orthogonal Decomposition (POD) to the pressure and the TPIV datasets. The first two POD modes show that the axisymmetric topology seen in the time averaged field is the result of the combination of different reflectional symmetry preserving states, each one featuring a hairpin vortex surrounded by an annular structure developing in proximity to the wake closure. The “head” and the “tails” of each hairpin vortex appear to be dynamically linked, as also proven by the existence of a second pair of modes, visible only in the TPIV dataset, featuring a twisted two-lobe structure. The analysis of the temporal evolution of the radial position of the centre of pressure over the model base reveals the existence of two different low-drag scenarios, characterised by the restoration of the axial symmetry or the selection of a single plane of reflectional symmetry. The first state is reported to become the only admissible low-drag configuration when the short-time wake dynamics are removed from the unsteady pressure signal.The near-wake of an axisymmetric body has been investigated using base pressure tappings and large scale Tomographic Particle Image Velocimetry (TPIV) at a Reynolds number of ReD = 3.2 × 105, based upon model diameter. Insights into the near-wake dynamics are provided by the application of Proper Orthogonal Decomposition (POD) to the pressure and the TPIV datasets. The first two POD modes show that the axisymmetric topology seen in the time averaged field is the result of the combination of different reflectional symmetry preserving states, each one featuring a hairpin vortex surrounded by an annular structure developing in proximity to the wake closure. The “head” and the “tails” of each hairpin vortex appear to be dynamically linked, as also proven by the existence of a second pair of modes, visible only in the TPIV dataset, featuring a twisted two-lobe structure. The analysis of the temporal evolution of the radial position of the centre of pressure over the model base reveals the existence of two diff... |
| Databáze: | OpenAIRE |
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