“…This observation aligns with the distinct peaks of the spectra of the velocity fluctuations behind the UC (figure 9a), in contrast to the relatively broader peaks observed behind the DC (figure 9b). The results also demonstrate that the SPOD Mode 1 contains the pertinent shedding dynamics of the large-scale energetic structures in the flow field, which agrees with previous bluff body studies (Yauwenas et al 2019;Chen et al 2022;Fang et al 2022;Chalmers et al 2023).…”
“…2022; Chalmers et al. 2023). Figure 14.Premultiplied energy spectra of the first five modes for ( a ) SC, ( b ) SR2, ( c ) SR4 and ( d ) SR6.…”
Section: Resultsmentioning
confidence: 99%
“…The region occupied by each cylinder was blanked out during the analysis. For each selected dominant frequency, the snapshot POD method (Sirovich 1987;Sen, Bhaganagar & Juttijudata 2007) was performed on the Fourier-transformed data using singular value decomposition (Fang, Tachie & Dow 2022;Chalmers, Fang & Tachie 2023;Essel et al 2023). The singular value decomposition computes the modes and eigenvalues (λ), which represent the energy content of each mode.…”
The unsteady wake interference of unequal-height tandem finite wall-mounted cylinders (FWMCs) fully submerged in a turbulent boundary layer (TBL) was investigated using time-resolved particle image velocimetry. The aspect ratios of the cylinders were fixed at
$h/d = 5.3$
for the upstream cylinder (UC) and
$H/d = 7.0$
for the downstream cylinder (DC) to achieve a height ratio of
$h/H = 0.75$
, where d is the diameter of the cylinders. The Reynolds number based on the cylinder diameter was
$Re = 5540$
and the submergence ratio was
$\delta /H = 1.2$
, where
$\delta $
is the TBL thickness. Three main flow regimes of tandem FWMCs were examined by varying the centre-to-centre spacing (
$s$
) between the cylinders: extended-body (
$s/d = 2$
), reattachment (
$s/d = 4$
) and co-shedding (
$s/d = 6$
) regimes. These test cases denoted as SR2, SR4 and SR6, respectively, were compared with a reference isolated cylinder (SC) with an aspect ratio similar to that of the DC. Spatio-temporal analysis of the flow field showed that the gap region of SR2 is characterized by a strong downwash of alternating low- and high-momentum fluid induced by the approach flow that is deflected from the unsheltered portion of the DC. In contrast, the gap region of SR4 and SR6 exhibited both downwash and upwash flow with a saddle point that moves closer to the mid-height of the UC as the spacing ratio increases. The upwash and downwash shear layers were associated with small-scale vortices with Strouhal numbers larger than that of the Kármán vortex shedding in the spanwise shear layers. The wake structure behind the DC was significantly altered compared with the SC due to sheltering effects, and the spacing ratio had a significant impact on the spatio-temporal evolution of the vortices.
“…This observation aligns with the distinct peaks of the spectra of the velocity fluctuations behind the UC (figure 9a), in contrast to the relatively broader peaks observed behind the DC (figure 9b). The results also demonstrate that the SPOD Mode 1 contains the pertinent shedding dynamics of the large-scale energetic structures in the flow field, which agrees with previous bluff body studies (Yauwenas et al 2019;Chen et al 2022;Fang et al 2022;Chalmers et al 2023).…”
“…2022; Chalmers et al. 2023). Figure 14.Premultiplied energy spectra of the first five modes for ( a ) SC, ( b ) SR2, ( c ) SR4 and ( d ) SR6.…”
Section: Resultsmentioning
confidence: 99%
“…The region occupied by each cylinder was blanked out during the analysis. For each selected dominant frequency, the snapshot POD method (Sirovich 1987;Sen, Bhaganagar & Juttijudata 2007) was performed on the Fourier-transformed data using singular value decomposition (Fang, Tachie & Dow 2022;Chalmers, Fang & Tachie 2023;Essel et al 2023). The singular value decomposition computes the modes and eigenvalues (λ), which represent the energy content of each mode.…”
The unsteady wake interference of unequal-height tandem finite wall-mounted cylinders (FWMCs) fully submerged in a turbulent boundary layer (TBL) was investigated using time-resolved particle image velocimetry. The aspect ratios of the cylinders were fixed at
$h/d = 5.3$
for the upstream cylinder (UC) and
$H/d = 7.0$
for the downstream cylinder (DC) to achieve a height ratio of
$h/H = 0.75$
, where d is the diameter of the cylinders. The Reynolds number based on the cylinder diameter was
$Re = 5540$
and the submergence ratio was
$\delta /H = 1.2$
, where
$\delta $
is the TBL thickness. Three main flow regimes of tandem FWMCs were examined by varying the centre-to-centre spacing (
$s$
) between the cylinders: extended-body (
$s/d = 2$
), reattachment (
$s/d = 4$
) and co-shedding (
$s/d = 6$
) regimes. These test cases denoted as SR2, SR4 and SR6, respectively, were compared with a reference isolated cylinder (SC) with an aspect ratio similar to that of the DC. Spatio-temporal analysis of the flow field showed that the gap region of SR2 is characterized by a strong downwash of alternating low- and high-momentum fluid induced by the approach flow that is deflected from the unsheltered portion of the DC. In contrast, the gap region of SR4 and SR6 exhibited both downwash and upwash flow with a saddle point that moves closer to the mid-height of the UC as the spacing ratio increases. The upwash and downwash shear layers were associated with small-scale vortices with Strouhal numbers larger than that of the Kármán vortex shedding in the spanwise shear layers. The wake structure behind the DC was significantly altered compared with the SC due to sheltering effects, and the spacing ratio had a significant impact on the spatio-temporal evolution of the vortices.
“…In case A, it is observed that the flow passes over the body without any visible reattachment along its surface. This is a result of the streamwise length of the bluff body not being sufficiently long enough for flow reattachment before reaching the trailing edge as also observed in previous experimental results [9]. As seen in Fig.…”
This paper analyzes the effect of streamwise length on the flow characteristics of elongated bluff bodies with small ground clearance using the Reynolds stress turbulence model. A fully developed turbulent boundary layer approach flow was specified as the inlet condition. Three cases with different elongation ratios (L/h) were considered for this analysis and a fourth case was employed for the validation of the simulation. Case A had an elongation ratio (L/h) of 1.0 while cases B and C had L/h of 2.0 and 3.0, respectively. The simulation was conducted at a Reynolds number Reh of 22500 for all cases. The mean velocities and Reynolds stresses are evaluated to gain a physical understanding of the flow dynamics around the bodies. The results showed that the flow passes over the body without any visible flow reattachment along its surface for case A. Cases B and C demonstrated flow reattachment occurring upstream of the trailing edge. However, in case B, the flow reattachment was of a shorter length and closer in proximity to the trailing edge. I.
The topic of flows around a near-wall square cylinder has garnered increasing attention in recent decades. However, there are a few publications that have focused on mitigating the occurrence of a substantial negative lift in near-wall flows. In light of this, the present study has developed a novel flow control strategy that covers porous media at inward corners of a near-wall square cylinder to address this problem. We achieve such a control strategy with the aid of a high-fidelity computational framework at Re = 1000. Direct numerical simulations are employed to account for accurate flow behaviors, and the Cartesian cut-cell method as well as an adaptive mesh refinement algorithm are advocated to simplify grid generation and reduce computational costs. Additionally, a quasi-microscopic flow model is introduced to model the porous medium pore structure, providing an intuitive and accurate description of internal flows within the porous medium. Six porous medium layouts are first designed, and their influences and mechanisms on flow control are assessed using the presented computational framework to identify an optimal strategy. The optimal strategy yields a notable reduction of 52.472% in the lift coefficient. The identified strategy is then applied to a case involving a near-wall square cylinder with a substantial negative lift, where a gap ratio of 0.6 is determined via parameterization. The capacity of the presented strategy in flow control of the near-wall square cylinder is fully explored and demonstrated via the consideration of different porosities. The results indicate that the most effective flow control is achieved when the porosity exceeds 90%, leading to a near-zero lift coefficient. Furthermore, the underlying mechanism contributing to the variations in flow control effectiveness due to different porosities is analyzed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
