Volumetric three-component particle tracking velocimetry flow measurements were taken to characterize the vortical structures past isolated and sheltered low-aspect-ratio finite wall-mounted circular cylinders (FWMCCs) immersed in a turbulent boundary layer. In addition to an isolated FWMCC case, sheltering effects are investigated for tandem arrangements at streamwise spacings of 2d and 6d, where d is the FWMCCs’ diameter. For each spacing, two height ratios <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$h_1/h_2 = 1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mn>1</mn> </msub> <mo stretchy="false">/</mo> <msub> <mi>h</mi> <mn>2</mn> </msub> <mo>=</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> and 0.5 are considered, where <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$h_1$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>h</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$h_2$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>h</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation> are the heights of the upstream and downstream FWMCCs, respectively. Measurements were taken for FWMCCs occupying 20% or less of the incoming boundary layer thickness. For the isolated FWMCC, the wake is dominated by two types of coherent vortical structures: an arch vortex with an inverted U shape and a streamwise counter-rotating vortex pair. The wake of sheltered FWMCCs is also dominated by a coherent U-shaped arch vortex and streamwise vortices; however, sheltering weakens these structures and affects their characteristics. For fully sheltered downstream FWMCCs (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">$h_1/h_2 = 1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mn>1</mn> </msub> <mo stretchy="false">/</mo> <msub> <mi>h</mi> <mn>2</mn> </msub> <mo>=</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>), the wake includes a single streamwise counter-rotating vortex pair originating at the upstream FWMCC. When the free end of the downstream FWMCC is unsheltered (<InlineEquation ID="IEq5"> <EquationSource Format="TEX">$h_1/h_2 = 0.5$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mn>1</mn> </msub> <mo stretchy="false">/</mo> <msub> <mi>h</mi> <mn>2</mn> </msub> <mo>=</mo> <mn>0.5</mn> </mrow> </math></EquationSource> </InlineEquation>), a streamwise counter-rotating vortex pair is induced at the downstream free end; this vortex pair merges, farther downstream, with the streamwise vortex pair originating at the upstream FWMCC. A third streamwise counter-rotating vortex pair is observed past the downstream FWMCC when it is sheltered by a FWMCC with <InlineEquation ID="IEq6"> <EquationSource Format="TEX">$h_1/h_2 = 0.5$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mn>1</mn> </msub> <mo stretchy="false">/</mo> <msub> <mi>h</mi> <mn>2</mn> </msub> <mo>=</mo> <mn>0.5</mn> </mrow> </math></EquationSource> </InlineEquation> positioned 2d upstream, further highlighting the dependence of the vortical structure organization on both the height ratio and streamwise spacing.

Vortical structures past isolated and sheltered wall-mounted cylinders immersed in a turbulent boundary layer

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发表日期：

2025年11月5日

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A. M. Hamed,
I. A. Spoor,
B. R. McAtee,
T. R. Belin

摘要

Volumetric three-component particle tracking velocimetry flow measurements were taken to characterize the vortical structures past isolated and sheltered low-aspect-ratio finite wall-mounted circular cylinders (FWMCCs) immersed in a turbulent boundary layer. In addition to an isolated FWMCC case, sheltering effects are investigated for tandem arrangements at streamwise spacings of 2d and 6d, where d is the FWMCCs’ diameter. For each spacing, two height ratios $h_1/h_2 = 1$ $h_{1} / h_{2} = 1$ and 0.5 are considered, where $h_1$ $h_{1}$ and $h_2$ $h_{2}$ are the heights of the upstream and downstream FWMCCs, respectively. Measurements were taken for FWMCCs occupying 20% or less of the incoming boundary layer thickness. For the isolated FWMCC, the wake is dominated by two types of coherent vortical structures: an arch vortex with an inverted U shape and a streamwise counter-rotating vortex pair. The wake of sheltered FWMCCs is also dominated by a coherent U-shaped arch vortex and streamwise vortices; however, sheltering weakens these structures and affects their characteristics. For fully sheltered downstream FWMCCs ( $h_1/h_2 = 1$ $h_{1} / h_{2} = 1$ ), the wake includes a single streamwise counter-rotating vortex pair originating at the upstream FWMCC. When the free end of the downstream FWMCC is unsheltered ( $h_1/h_2 = 0.5$ $h_{1} / h_{2} = 0.5$ ), a streamwise counter-rotating vortex pair is induced at the downstream free end; this vortex pair merges, farther downstream, with the streamwise vortex pair originating at the upstream FWMCC. A third streamwise counter-rotating vortex pair is observed past the downstream FWMCC when it is sheltered by a FWMCC with $h_1/h_2 = 0.5$ $h_{1} / h_{2} = 0.5$ positioned 2d upstream, further highlighting the dependence of the vortical structure organization on both the height ratio and streamwise spacing.