Shedding Patterns Research Articles

Switching events of wakes shed from two short flapping side-by-side cylinders

Abstract The wakes shed alternatively from two long stationary side-by-side cylinders have long been an issue in many engineering applications, such as wind energy harvesting schemes that utilize vortex-induced vibrations. In this study, switching events of the wakes shed from two “short,” “flapping” side-by-side cylinders are investigated. To this end, the flow visualization and spectral analysis of the time-resolved data from hot-wire anemometers and the piezoelectric mount of flapping cylinders are carried out. Measurements are conducted with differing center-to-center spacing normalized by a single cylinder diameter (T/D) – gap ratio, and length-to-diameter ratio (L/D) in a Reynolds number range of 800 ≤ ReD ≤ 16,000. The results demonstrate the transition of wake shedding patterns, sequentially from a single bluff body wake, first bi-stable wakes, tri-stable wakes, second bi-stable wakes, and eventually to coupled wakes as the gap ratio is increased. Furthermore, the role of shortness and flapping of the two cylinders in determining the wake kinematics is elucidated, and the transitional sequences and switching of dominant shedding frequencies are detailed.

Self-selection of flow instabilities by acoustic perturbations around rectangular cylinder in cross-flow

This work experimentally investigates the flow structure around a rectangular cylinder with an aspect ratio of 2 under varying incidence angles to examine how acoustic perturbations modify and modulate the unsteady flow instabilities. In the absence of acoustic excitation, the angle of incidence is found to markedly influence the flow topology and the natural shedding pattern altering the vortex formation length and wake dynamics. With acoustic perturbations, it is observed that for incidence angles $\alpha = 0^{\circ }$ and $\alpha = 5^{\circ }$ , the masked impinging leading-edge vortex (ILEV)/trailing-edge vortex shedding (TEVS) instability modes of $n= 1$ and $n= 2$ become evident when their frequencies coincide with the frequencies of the acoustic perturbations (i.e. resonant condition). Both trailing-edge and leading-edge vortices were found to be modulated by the acoustic pressure cycle. These instability modes, which are naturally present under non-resonant conditions for significantly higher aspect ratios, highlight the role of incidence angle and self-excited acoustic resonance in virtually augmenting the streamwise length of the cylinder, thereby facilitating the emergence and sustenance of the ILEV/TEVS shedding pattern.

Effects of gap entrance configuration on gap resonances between two free-heaving barges: Vortex shedding behaviors

This paper mainly concentrates on the influences of the vortex shedding pattern and the behaviors of the generated vortex bubbles on the hydrodynamic performances of two identical side-by-side barges when encountering the linear and nonlinear gap resonances. The vortex shedding pattern around the entrance of the gap is highly influenced by the gap entrance configuration, and thus, two kinds of gap entrance configurations, i.e., round edge and square edge, are taken into account. The vortex shedding patterns are identified during the linear and nonlinear gap resonances for all conditions. Meanwhile, the effects of incident-wave height and barges' heave responses are considered when interacting with different edge shapes. Numerical results demonstrated that both the gap resonances and barges' heave responses are influenced by the vortex generation pattern. Significantly, the magnitudes of the wave elevation at gap during the linear and nonlinear gap resonances are influenced by the coupling effect between the vortex bubbles' pre-behaviors, i.e., vortex shedding pattern, and their post-behaviors, i.e., vortex bubbles' behaviors post-shedding from shear layers, underscoring the importance of understanding vortex shedding patterns and the behaviors of vortex bubble in investigating the gap resonances.

Kármán Vortex Street in Bose-Einstein Condensate with PT Symmetric Potential

Abstract Kármán vortex street not only exists in nature, but also widely appears in engineering practice, which is of great significance for understanding superfluid. And parity-time (PT) symmetric potential provides a good platform for the study of Kármán vortex street. In this paper, different patterns of vortex shedding formed behind PT symmetric potential in Bose-Einstein condensate (BEC) are
simulated numerically. Kármán vortex street and others are discovered to emerge in the wake of a moving obstacle with appropriate parameters. Compared with BEC without PT symmetric potential, the frequency and amplitude of the drag force are more complex. The parametric regions of the combined modes are scattered around the Kármán vortex street. Numerical simulations indicate that the imaginary part of the PT symmetric potential affects the vortex structure patterns. Finally, we proposed an experimental protocol that may observe Kármán vortex street.

Numerical investigation of cavity dynamics and cavitation-induced vibrations of a flexible hydrofoil

This work investigates the cavitation and fluid–structure interaction characteristics of a flexible NACA0015 hydrofoil. The simulation incorporates the Zwart–Gerber–Belamri cavitation model and two-way fluid–structure interactions. The detached eddy simulation method is employed to analyze the impact of cavitation and elastic deformation on hydrodynamic performance. The vibrational response and cavitating flow field around the hydrofoil are investigated. The results show that the vibrational mode of the elastic hydrofoil shifts with increasing flow speed. Furthermore, the vertical vibrational displacement of the hydrofoil aligns with the variations in cavitation volume in the flow field. The structural vibrational deformation of an elastic hydrofoil notably affects the evolution of cavitation. Additionally, fluid–structure interaction in the presence of cavitation influences the pattern of vortex shedding wakes in the flow field. The results of this study can serve as a reference for the design of hydrofoils constructed from composite elastic materials.

Pathobiological characterization of a novel duck picornavirus in duck in China

A novel strain of duck picornavirus was isolated from duck tissue in Taian, Shandong Province, in 2017 in our laboratory. The virus was amplified in specific-pathogen-free (SPF) chicken embryos, purified and then analyzed by whole genome sequencing, which revealed a new duck-derived small RNA virus that was designated as Duck/FC22/China/2017 (FC22, GenBank accession no. MN102111) based on its genome structure and phylogenetic relationship. An in-depth study revealed that the virus grew well on the Leghorn male hepatoma (LMH) cell line. After propagation of the virus, SPF ducks were inoculated for pathogenicity tests, and their mental state, growth and development were observed after inoculation; the ducks were dissected to observe the organs and histopathological changes. A TaqMan fluorescence quantitative PCR method was utilized to detect the proliferation and shedding patterns of the virus within the ducks, while the SYBR Green I fluorescence quantitative PCR method was used to assess cytokine expression levels in the organs. The results showed that following inoculation with the FC22 strain, the mental status of the SPF ducks remained unchanged. Mild oedema was observed in some tissue organs during dissection; however, no pathological changes, such as congestion or degeneration, were noted. Histopathological analysis revealed cellular necrosis in organs, including the heart, liver, and bursa of Fabricius, as well as a reduced volume and deep staining of certain neurons in the cerebrum. Following infection, the virus titres in various organs and in cloacal swabs of the SPF ducks peaked on the first day before gradually decreasing daily. By the 10th d, the virus titres in all organs had decreased to less than 101 copies/μL. Additionally, notable alterations were observed in the expression levels of the cytokines IFNα, IL6, IL10, and TNFα. This indicates that the FC22 strain does not cause significant disease in ducks. This report presents the initial study on a recently discovered picornavirus, offering a thorough and methodical examination of its pathogenic characteristics and provides a reference for the clinical evaluation and scientific strategies for the prevention and treatment of this particular picornavirus.

Effects of aspect ratio on flow characteristics on free surface-mounted rectangular cylinders

Turbulent flow characteristics around free surface-mounted rectangular cylinders of different streamwise aspect ratios (AR=1, 2, 2.5, 3, 4, 5, and 8 denoted as AR1, AR2, AR2.5, AR3, AR4, AR5, and AR8, respectively) at a Reynolds number based on the freestream velocity and cylinder height, Reh = 11100, were investigated experimentally using a time-resolved particle image velocimetry system. The results reveal distinct flow behaviors for different aspect ratios. The separated shear layer is shed directly into the wake for AR1, while AR2 and AR2.5 exhibits intermittent reattachment on the cylinder and direct shedding into the wake. However, for AR≥3 cylinders, the separated shear layer reattaches onto the cylinder and is later shed into the wake after subsequent separation from the trailing edge of the cylinder. Comparative analysis with previous studies on rectangular cylinders in uniform flow and wall-mounted conditions demonstrates similarities in reattachment behavior on the cylinder to uniform flow cases and wake reattachment mechanism akin to wall-mounted cylinders subjected to a thin turbulent boundary layer. The Reynolds stresses, turbulence production, and vortex shedding patterns examined with frequency spectra and proper orthogonal decomposition of velocity fluctuations exhibit significant dependence on streamwise aspect ratio.

The Use of Wastewater Surveillance to Estimate SARS-CoV-2 Fecal Viral Shedding Pattern and Identify Time Periods with Intensified Transmission.

Wastewater-based surveillance is an important tool for monitoring the COVID-19 pandemic. However, it remains challenging to translate wastewater SARS-CoV-2 viral load to infection number, due to unclear shedding patterns in wastewater and potential differences between variants. We utilized comprehensive wastewater surveillance data and estimates of infection prevalence (i.e., the source of the viral shedding) available for New York City (NYC) to characterize SARS-CoV-2 fecal shedding pattern over multiple COVID-19 waves. We collected SARS-CoV-2 viral wastewater measurements in NYC during August 31, 2020 - August 29, 2023 ( N = 3794 samples). Combining with estimates of infection prevalence (number of infectious individuals including those not detected as cases), we estimated the time-lag, duration, and per-infection fecal shedding rate for the ancestral/Iota, Delta, and Omicron variants, separately. We also developed a procedure to identify occasions with intensified transmission. Models suggested fecal viral shedding likely starts around the same time as and lasts slightly longer than respiratory tract shedding. Estimated fecal viral shedding rate was highest during the ancestral/Iota variant wave, at 1.44 (95% CI: 1.35 - 1.53) billion RNA copies in wastewater per day per infection (measured by RT-qPCR), and decreased by ∼20% and 50-60% during the Delta wave and Omicron period, respectively. We identified around 200 occasions during which the wastewater SARS-CoV-2 viral load exceeded the expected level in any of 14 sewersheds. These anomalies disproportionally occurred during late January, late April - early May, early August, and from late-November to late-December, with frequencies exceeding the expectation assuming random occurrence ( P < 0.05; bootstrapping test). These estimates may be useful in understanding changes in underlying infection rate and help quantify changes in COVID-19 transmission and severity over time. We have also demonstrated that wastewater surveillance data can support the identification of time periods with potentially intensified transmission.

Large-eddy simulation of vortex-induced vibration of a circular cylinder at Reynolds number 10 000

The canonical scenario of cross-flow vortex-induced vibration (VIV) of a circular cylinder in the turbulent regime, which has been studied by several physical experiments in the literature, is reexamined in this study through high-fidelity large-eddy simulations (LES) at a Reynolds number 104. The VIV response (including vibration amplitude and frequency) and hydrodynamic coefficients predicted by the present LES agree with the experimental results better than previous numerical attempts. In addition, several phenomena reported by previous experimental studies are confirmed numerically for the first time. After validating against the experiments, new VIV characteristics and physical mechanisms are explored with confidence. First, a collective analysis on the frequency spectra of the displacement, lift, and velocity signals provides a complete picture of the frequency response of the system. In contrast, the use of a single signal may miss certain aspects of the frequency response, so that caution should be exercised. Second, spanwise correlation of primary vortex shedding is examined, where relatively low correlations in the upper and lower branches are likely because the vortex shedding patterns involve complex vortex generation and interaction. Third, the effect of mass ratio (m*) of the cylinder on the VIV response is analyzed with a range of m* (=1.4–3.4) relevant to cylindrical structures used in offshore engineering (such as subsea pipelines). The variations in the amplitude response, frequency response, and hydrodynamic coefficients with m* and reduced velocity are examined in detail. The present results suggest that a lighter pipeline is more susceptible to the onset of VIV.

Shedding-scheme transition of hemisphere near wake dependent on Reynolds number

The shedding-scheme transition of hemispherical wake is investigated with time-resolved tomographic particle image velocimetry. Experiments are carried out with Reynolds numbers based on the hemisphere radius R in the range of Rer=924–2315, crossing the critical value of Rer≈2000. The variation of the hemispherical wake across the critical Reynolds number is carefully studied, and a detailed mechanism of the shedding-scheme transition is explored. A singular-shedding pattern of hairpin vortices at a low Rer is replaced by a pairing-shedding pattern at a moderate Rer, and finally, a less ordered wake and an unstable shedding pattern are observed at Rer &amp;gt; 2000. The onset of the pairing-shedding pattern is due to a streamwise modulation caused by the varicose modes, which is related to the Kelvin–Helmholtz (K–H) instability. Consequently, the pseudo-periodicity induced by the K–H instability is observed in the wake. When Rer &amp;gt; 2000, the stronger sinuous modulation intensifies interactions among the hairpin vortices, leading to frequent absorption and annihilation of those coherent structures, which further makes the dominant frequency of main hairpin vortices halved downstream.

Clinical and Diagnostic Findings in Dogs Infected with Trichuris vulpis: A Retrospective Study.

Trichuris vulpis is a parasite of the large intestine of canids and has a global distribution. Despite its well-established epidemiology, the question of its pathogenicity in dogs remains debated. It has been suggested that younger age and concurrent infection with Ancylostoma caninum may be responsible for more severe clinical presentations. This retrospective study aimed to describe the clinical and diagnostic features of T. vulpis-infected dogs and to compare these findings with dogs infected with both T. vulpis and other intestinal parasites (poly-infected dogs). Forty-five dogs were included, with twenty-five being solely infected by T. vulpis and twenty poly-infected dogs. Only weight loss was more frequent (p = 0.006) in poly-infected dogs compared to T. vulpis mono-infected dogs. No significant differences were observed in laboratory abnormalities between mono-infected and poly-infected dogs. Only diarrhea was more frequent (p = 0.007) in younger dogs compared to adults. The egg shedding pattern was significantly higher (p = 0.04) among adult dogs compared to young ones, and there was a significant positive correlation between egg shedding and age (r = 0.41; p = 0.005). These findings suggest that T. vulpis might be responsible for both clinical signs and laboratory abnormalities in dogs, irrespective of the host's age and the presence of other intestinal parasites.

Shedding of Cavitation Clouds in an Orifice Nozzle

Focused on the unsteady property of a cavitating water jet issuing from an orifice nozzle in a submerged condition, this paper presents a fundamental investigation of the periodicity of cloud shedding and the mechanism of cavitation cloud formation and release by combining the use of high-speed camera observation and flow simulation methods. The pattern of cavitation cloud shedding is evaluated by analyzing sequence images from a high-speed camera, and the mechanism of cloud formation and release is further examined by comparing the results of flow visualization and numerical simulation. It is revealed that one pair of ring-like clouds consisting of a leading cloud and a subsequent cloud is successively shed downstream, and this process is periodically repeated. The leading cloud is principally split by a shear vortex flow along the nozzle exit wall, and the subsequent cloud is detached by a re-entrant jet generated while a fully extended cavity breaks off. The subsequent cavitation cloud catches the leading one, and they coalesce over the range of x/d≈1.8~2.5. Cavitation clouds shed downstream from the nozzle at two dominant frequencies. The Strouhal number of the leading cavitation cloud shedding varies from 0.21 to 0.29, corresponding to the injection pressure. The mass flow rate coefficient fluctuates within the range of 0.59~0.66 at the same frequency as the leading cloud shedding under the effect of cavitation.

Viral shedding pattern of severe fever with thrombocytopenia syndrome virus in severely ill patients: A prospective, Multicenter cohort study

BackgroundSevere fever with thrombocytopenia syndrome (SFTS) is spreading rapidly in Asia. The pathway of SFTS virus shedding from patient and specific use of personal protective equipments (PPEs) against viral transmission have rarely been reported. The study was to determine SFTS virus (SFTSV) shedding pattern from the respiratory, digestive and urinary tract to outside in patients. Methods: Patients were divided into mild and severe groups in three sentinel hospitals for SFTS in Anhui province from April 2020 to October 2022. SFTSV level from blood, throat swabs, fecal/anal swabs, urine and bedside environment swabs of SFTS patients were detected by qRT-PCR. Specific PPEs were applied in healthcare workers contacting with the patients who had oropharyngeal virus shedding and hemorrhagic signs. ResultsA total of 189 SFTSV-confirmed patients were included in the study, 54 patients died (case fatality rate, 28.57 %). Positive SFTSV in throat swabs (T-SFTSV), fecal/anal swabs (F-SFTSV) and urine (U-SFTSV) were detected in 121 (64.02 %), 91 (48.15 %) and 65 (34.4 %) severely ill patients, respectively. The levels of T-SFTSV, F-SFTSV and U-SFTSV were positively correlated with the load of SFTSV in blood. We firstly revealed that SFTSV positive rate of throat swabs were correlated with occurrence of pneumonia and case fatality rate of patients (P < 0.0001). Specific precaution measures were applied by healthcare workers in participating cardiopulmonary resuscitation and orotracheal intubation for severely ill patients with positive T-SFTSV, no event of SFTSV human-to-human transmission occurred after application of effective PPEs. ConclusionsOur research demonstrated SFTSV could shed out from blood, oropharynx, feces and urine in severely ill patients. The excretion of SFTSV from these parts was positively correlated with viral load in the blood. Effective prevention measures against SFTSV human-to-human transmission are needed.

Evaluation of bovine coronavirus in Korean native calves challenged through different inoculation routes

Bovine coronavirus (BCoV) is a pneumoenteric virus that can infect the digestive and respiratory tracts of cattle, resulting in economic losses. Despite its significance, information regarding BCoV pathogenesis is limited. Hence, we investigated clinical signs, patterns of viral shedding, changes in antibody abundance, and cytokine/chemokine production in calves inoculated with BCoV via intranasal and oral. Six clinically healthy Korean native calves (< 30 days old), initially negative for BCoV, were divided into intranasal and oral groups and monitored for 15 days post-infection (dpi). BCoV-infected calves exhibited clinical signs such as nasal discharge and diarrhea, starting at 3 dpi and recovering by 12 dpi, with nasal discharge being the most common symptoms. Viral RNA was detected in nasal and fecal samples from all infected calves. Nasal shedding occurred before fecal shedding regardless of the inoculation route; however, fecal shedding persisted longer. Although the number of partitions was very few, viral RNA was identified in the blood of two calves in the oral group at 7 dpi and 9 dpi using digital RT-PCR analysis. The effectiveness of maternal antibodies in preventing viral replication and shedding appeared limited. Our results showed interleukin (IL)-8 as the most common and highly induced chemokine. During BCoV infection, the levels of IL-8, monocyte chemoattractant protein-1, and macrophage inflammatory protein-1β were significantly affected, suggesting that these emerge as potential and reliable biomarkers for predicting BCoV infection. This study underscores the importance of BCoV as a major pathogen causing diarrhea and respiratory disease.

Harnessing flow-induced vibrations for energy harvesting: Experimental and numerical insights using piezoelectric transducer.

Flow-induced vibrations (FIV) were considered as unwanted vibrations analogous to noise. However, in a recent trend, the energy of these vibrations can be harvested and converted to electrical power. In this study, the potential of FIV as a source of renewable energy is highlighted through experimental and numerical analyses. The experimental study was conducted on an elastically mounted circular cylinder using helical and leaf springs in the wind tunnel. The Reynolds number (Re) varied between 2300-16000. The motion of the cylinder was restricted in all directions except the transverse direction. The micro-electromechanical system (MEMS) was mounted on the leaf spring to harvest the mechanical energy. Numerical simulations were also performed with SST k-ω turbulence model to supplement the experiments and were found to be in good agreement with the experimental results. The flow separation and vortex shedding induce aerodynamic forces in the cylinder causing it to vibrate. 2S vortex shedding pattern was observed in all of the cases in this study. The maximum dimensionless amplitude of vibration (A/D) obtained was 0.084 and 0.068 experimentally and numerically, respectively. The results showed that the region of interest is the lock-in region where maximum amplitude of vibration is observed and, therefore, the maximum power output. The piezoelectric voltage and power output were recorded for different reduced velocities (Ur = 1-10) at different resistance values in the circuit. It was observed that as the amplitude of oscillation of the cylinder increases, the voltage and power output of the MEMS increases due to high strain in piezoelectric transducer. The maximum output voltage of 0.6V was observed at Ur = 4.95 for an open circuit, i.e., for a circuit with the resistance value of infinity. As the resistance value reduced, a drop in voltage output was observed. Maximum power of 10.5μW was recorded at Ur = 4.95 for a circuit resistance of 100Ω.

Vortex shedding behind porous flat plates normal to the flow

This work examines the influence of body porosity on the wake past nominally two-dimensional rectangular plates of fixed width $D$ in the moderate range of Reynolds numbers $Re = UD/\nu$ (with $U$ the incoming velocity and $\nu$ the kinematic viscosity) between 15 000 and 70 000. With porosity $\beta$ defined as the ratio of open to total area of the plate, it is well established that as porosity increases, the wake shifts from the periodic von Kármán shedding behaviour to a regime where this vortex shedding is absent. This change impacts the fluid forces acting on the plate, especially the drag, which is significantly lower for a wake without vortex shedding. We analyse experimentally the transition between these two regimes using hot-wire anemometry, particle-image velocimetry and force measurements. Coherence and phase measurements are used to determine the existence of regular, periodic vortex shedding based on the velocity fluctuations in the two main shear layers on either side of the wake. Results show that, independent of $Re$ , the wake exhibits the classical Kármán vortex shedding pattern for $\beta &lt;0.2$ but this is absent for $\beta &gt;0.3$ . In the intermediate range, $0.2&lt;\beta &lt;0.3$ , there is a transitional regime that has not previously been identified; it is characterised by intermittent shedding. The flow alternates randomly between a vortex shedding and a non-shedding pattern and the total proportion of time during which vortex shedding is observed (the intermittency) decreases with increasing porosity.

Aerodynamic characteristics and wake formation behind a pair of side-by-side rectangular cylinders using the lattice Boltzmann method

In this work, the lattice Boltzmann method is used to numerically analyze the interactions of flowing fluid with two side-by-side rectangular cylinders at a fixed Reynolds number of 150. The gap ratios between the cylinders are varied from 0.5 to 5 while the aspect ratios of both cylinders are varied from 0.25 to 4. The deflected, bistable, flip-flopping, chaotic, single bluff body, two pairs’ street of anti-phase vortex shedding, anti-phase synchronized, and in-phase non-synchronized wake patterns are observed upon varying the aspect ratios as well as the gap ratios. The observed results show that the mean drag coefficients of both side-by-side rectangular cylinders, as well as that of the single cylinder, exhibit decreasing trends till the aspect ratio = 2 and become almost constant afterward. The Strouhal number varies abruptly at the gap ratio of 0.5 and becomes steady for gap ratios = 2 and 5. The root-mean-square values of lift coefficients of two side-by-side rectangular cylinders exhibit variations till the aspect ratio equal to 1.5 and then becomes constant afterward. This study also reveals that an increment in aspect ratios results in the minimization of the drag force and controls the wake, while the increment in gap ratio results in stabilizing the chaos produced in the flow structure due to jet flow influence. The wake patterns in this study are found to be consistent with the numerical and experimental work of other researchers.

Effect of topographical pattern on vortex shedding and heat transfer phenomena in power-law fluid flow around a rotating cylinder

The present numerical investigation studies the momentum and heat transfer phenomena from a heated rotating patterned cylinder in the vortex shedding regime. In particular, the effect of surface patterns ( ω , δ ), fluid behavior ( 0.4 ≤ n ≤ 1.6 ), cylinder rotation speed ( 0.5 ≤ α ≤ 2 ), and Prandtl number ( 1 ≤ Pr ≤ 100 ) at Reynolds number 100 on the force coefficients and Nusselt number are studied. Vorticity and isotherm profiles demonstrate the flow dynamics and heat transfer characteristics. According to the findings of this study, the formation of the vortex (including its size, shape, and number of vortices) and the time period during which the vortex shedding pattern repeats itself demonstrates a dependency on the shape of the cylinder, fluid behavior, and rotating speed. It has been noted that a significant decrease in the frequency of vortex shedding occurs on adding topographical patterns. Additionally, it has been noticed that on increasing rotational speed, vortex shedding can be suppressed for all fluid behaviors. Numerical simulation results reveal that the average drag coefficient ( C ¯ D ) for a rotating patterned cylinder decreases with increasing rotational speed ( α ), and it further reduces on increase in pattern frequency ( ω ) and amplitude ( δ ) compared to a smooth circular cylinder. The shear-thinning fluid behavior helps to dissipate the heat from the cylinder to the surrounding fluid. Conversely, shear-thickening fluid behavior exhibits the opposite trend.

Turbulent transports in the flow around a rectangular cylinder with different aspect ratios

The flow around a rectangular cylinder exhibits intricate features, encompassing phenomena such as separation, reattachment, boundary layer transition, and relaminarization. This study explores the intense transport of turbulent fluctuations in these complex flow phenomena, including momentum and turbulent kinetic energy (TKE) transport, for three aspect ratios (L/D=5,10 and 15) at a medium Reynolds number (Re=1000). The connection between these transports and crucial vortical structures is elucidated for the first time. On the lateral side of the cylinder, strong momentum transport occurs, dominated by ejection and sweep events associated with the hairpin vortex. The generation of the LE vortex also leads to active TKE production. The existence of the LE separation bubble, as well as the relaminarization of the downstream boundary layer at L/D=10 and 15, affects the distribution of production terms. This perspective offers an effective yet novel approach that has not been previously addressed in prior researches. The redistribution of TKE results in a disturbance growth, linked to boundary layer transition. The source term reveals that streamwise TKE carried into the recirculating region is closely related to the frequency prior amplified by the LE shear layer. In the wake behind TE, turbulent transports are influenced by vortex shedding patterns.

Coupling of the immersed boundary and Fourier pseudo-spectral methods applied to solve fluid–structure interaction problems

The current manuscript addresses fluid–structure interaction (FSI) problems to the analysis of vortex-induced vibration (VIV), employing the methodology designated as IMERSPEC2D. The approach seamlessly integrates the Fourier pseudo-spectral method (FPSM) and the immersed boundary method (IBM) to solve the Navier–Stokes (NS) and continuity equations. Simultaneously, the effects of cylindrical structure, involving 1 and 2 degrees of freedom (d.o.f.) are simulated, by incorporating structural motion equations into NS via the IBM source term and implementing a two-way FSI algorithm. In the paper are presented the comparison of low and high-order temporal integration methods applied to solve the dynamic behavior of the structure and the dimensionless of the cylinder’s structural motion equations, resulting in an increase in computational time step from 1E(-9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-9$$\\end{document}) to 1E(-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-3$$\\end{document}). Validation results to refined mesh simulations include the accurate representation of the lock-in phenomenon to simulations of 1 d.o.f. obtaining the range between reduced velocity 5.456 and 5.568 and the maximal amplitude is 0.352. Notably, the eight-shape pattern of the 2 d.o.f. cylinder displacement is obtained and the formation of C2S wake patterns is achieved, as presented by other authors. In conclusion, the dimensionless approach reduces computational time, while the high-order both of IMERSPEC methodology and time advancement integration to FSI improve the results of the cylinder’s motion and alters distinct vortex shedding patterns in fluid dynamics.