Wake Instability Research Articles

On the short-wavelength three-dimensional instability in the cylinder wake

We examine the mechanisms responsible for the onset of the three-dimensional mode B instability in the wake behind a circular cylinder. We show that it is possible to explicitly account for the stabilising effect of spanwise viscous diffusion and then demonstrate that the remaining mechanisms involved in this short-wavelength instability are preserved in the limit of zero wavelength. Using the resulting simplified equations, we show that perturbations in different fluid particles interact only through the in-plane viscous diffusion which turns out to have a destabilising effect. We also show that in the presence of viscous diffusion, the closed trajectories which had been conjectured to play a crucial role in the onset of the mode B instability are not actually a prerequisite for the growth of mode B type perturbations. We combine these observations to identify the three essential ingredients for the development of the mode B instability: (i) the amplification of perturbations in the braid regions due to the stretching mechanism; and the spreading of perturbations through (ii) viscous diffusion, and (iii) cross-flow advection which transports fluid between the two braid regions on either side of the cylinder. Finally, we develop a simple criterion that allows the prediction of the regions where three-dimensional short-wavelength perturbations are amplified by the stretching mechanism. The approach used in our study is general and has the potential to give insights into the onset of three-dimensionality via short-wavelength instabilities in other flows.

Investigation of the Coupling Between the Dynamics of Vortical Structures and Flame Stability in Bluff-Body Premixed Combustion Using Extended Spectral Proper Orthogonal Decomposition

Abstract Large eddy simulation data of a bluff-body stabilized flame are analyzed using spectral proper orthogonal decomposition (SPOD) to investigate: (i) the role of flame-vortex interactions in the dominant flow dynamics, and (ii) how the proper choice of the cross-spectral density (CSD) defining SPOD can assist in identifying the underlying dynamics. Bluff-body flame holders aim to achieve stable flames under lean premixed conditions to minimize pollutant emissions. The recirculation region induced by the body promotes the mixing of hot combustion products with unburnt gases, preventing the global blowoff. However, the coupling between the shear layers and flame-induced vorticity sources can result in large flow structures that either contribute to increased flame stability or exhibit features typical of the early stages of flame blowout. SPOD is a data-driven technique remarkably powerful in extracting low-dimensional models. For each frequency, it computes a basis of orthogonal modes that maximizes the content of a predefined CSD in the leading modes. By choosing physically-relevant variables to construct the CSD, different physics can be explored, which is used here to investigate the coupled dynamics between the flame-induced baroclinic torque, vortical structures, and the temperature field. The results show that the vorticity and temperature fields exhibit low-dimensional dynamics characterized by a narrowband frequency and its harmonics; these dynamics are varicose oscillations of the flame region, governed by the baroclinic torque. Sinuous oscillations typical of wake instability for non-reactive flows are also present, suggesting a competition between them.

Volumetric Reconstruction Of Stagnated Wake Structures In Adverse Pressure Gradient

To gather insights about turbulent structures of a wake in adverse pressure gradient, a wind tunnel model is investigated with PIV methods. A flat plate of L = 1.058 m at zero angle of attack is placed in the MUB wind tunnel at TU Braunschweig. The wake convects downstream into a carefully designed diffuser, where it undergoes a pressure increase of ∆c p = +0.6. Wakes, with the common example of a cylinder shedding van-Karman vortices, are generally prone to instability. The wake instability of the sharp-edged plate is attenuated by the adverse pressure gradient, manifesting in large coherent structures that carry up to 37 % of the turbulent kinetic energy. While the primary shedding motion is effectively a quasi-2D motion, a secondary mode of is also observed: Over the span S = 1.3 m of the wake, it organizes in three distinct cells. Their motion is similar to "owl-eyes", that are known to appear on separated flow over smooth 2D bodies. The presence of these modes reduces the average flow velocity in the wake centre up to stagnation in the mean sense. Because stagnation and shedding does occur far away from any solid surfaces, this test case offers excellent observability of the phenomenon with PIV methods. RANS results of this setup cannot predict the flow stagnation accurately. Because the shedding frequency is low compared to freestream velocity, scale and time resolving IDDES results need to run many convective time units until the observed instability develops. While the original goal of observing small scale turbulent wake structures is compromised by the large shedding modes, the observation gives an insight on wake-bursting phenomena that occur on multi-element high-lift devices. The mode shedding and consequent wake stagnation is sensitive to the Reynolds-number (Re = [1.6 ... 3.2] · 10 6 ) as well as to the initial boundary layer thickness of the flat plate.

Advancements in the Understanding of Single‐Bubble Dynamics: Integrated Experimental and Simulation Studies

Because of wake instability, bubbles always ascend along an unstable path, which is not considered when simulating their movement in steel refining and continuous casting systems. Utilizing the 3D shadow image method, a quantitative characterization of the bubble trajectories is conducted to establish a bubble path oscillation model considering the zigzag lateral movement of bubbles due to asymmetric wake shedding. This model is incorporated into a rectilinear bubble motion model within the Lagrangian framework and then used to simulate the free ascent of single bubbles within the 2.15–2.55 mm range. The predicted bubble ascent velocities and trajectories agree well with the experimental. The spatial position, velocity, acceleration, forces, volume swept by bubbles, and bubble residence time are discussed. The results shown that the dominant force in the horizontal direction is the lateral force, followed by the drag and virtual mass force. Compared to the rectilinear path model, the volume swept by bubbles with initial diameters of 2.15, 2.25, 2.34, 2.45, and 2.55 mm in this model increases by 30.8%, 32.0%, 34.0%, 31.5%, and 29.6%, respectively. These findings help accurately predict the path of bubbles and also may contribute to a better understanding of bubble dynamics in bubble metallurgy and clean steel production.

Wake structure of an array of cylinders in shallow flow

Although there is a range of approaches for classifying the wake structure behind an array of obstacles, these approaches provide inconsistent results across different array systems. This motivates the present study to integrate and reconcile these approaches into one that is consistent across different systems. This new, transferable classification approach is based on the dimensionless flow blockage of the array and the wake stability parameter. To demonstrate this approach, a series of laboratory experiments was conducted to characterise the wake structure behind an array of emergent cylinders across a practically relevant parameter space that has not previously been explored. Two arrays with the same values of flow blockage and wake stability parameters but different sizes display the same wake structure, demonstrating the controlling influence of these two parameters on the wake structure. This approach classifies four different wake structures, which are distinct in that they display differences in instantaneous and time-averaged flow fields, temporal velocity oscillations, shear layer growth and the length of the steady wake region. The dependence of the wake structure on the two parameters is a consequence of (i) the controlling influence of blockage on the fraction of incident flow passing through the array and (ii) the ability of shallowness to suppress wake instabilities and, to a lesser extent, also influence the velocity through the array. This paper provides a predictive framework for the wake structure based on knowledge of the array geometry, and the depth and velocity of incident flow across the entire relevant practical parameter space.

The onset of instability and bifurcations in the transitional wake of two tandem square cylinders

Unsteady three-dimensional simulations are performed to elucidate the hidden transitional flow dynamics and Hopf bifurcations along the topological corelines of the created von Kármán streets behind a pair of square cylinders positioned in tandem. Our simulations provide significant new insight into the three-dimensional wake evolution and governing flow physics. We explain how pressure, velocity, and vorticity fluctuation along the Kármán vortex corelines in the increasingly unstable wake amplify, facilitating the growth of various modal instability patterns. The existing knowledge of wake transition through the intertwining of modes A, B, and C instabilities and associated linear stability analysis helped to gain some insight into the overall wake feature. The current study explains how exactly the transitional disturbances physically spread behind a pair of inline and tandem cylinders through the self-excited spanwise-periodic oscillation of the wake and created a sequence of variable length scaled Hopf bifurcations and their swapping for varied gaps between the cylinders and Reynolds number. The growth of a slow mode of the spectral frequency at the bifurcation points seemed crucial in initiating the near-transitional flow irregularity.

Influence of the tip speed ratio on the wake dynamics and recovery of axial-flow turbines

Detached eddy simulation is employed to investigate the wake development downstream of the rotor of an axial-flow turbine and its dependence on the tip speed ratio. In this study, we found that the trend of the momentum deficit as a function of the rotational speed shows opposite directions in the near wake and further downstream. While the momentum deficit in the near wake increases with the rotational speed, it decreases further downstream. For instance, we found that at six diameters downstream of the rotor the streamwise velocity in its wake recovered to about 30% of its free-stream value at the lowest simulated tip speed ratio of 4, while its recovery was equal to about 65% at the largest tip speed ratio of 10. This is due to the earlier breakdown of the tip vortices. The results of the computations demonstrate indeed that mutual inductance phenomena between tip vortices, promoting pairing events and the eventual instability of the helical structures, occur at shorter downstream distances for higher values of tip speed ratio. Wake instability enhances the process of wake recovery, especially due to radial advection. Therefore, higher rotational speeds do not promote wake recovery through more intense tip vortices, but through their greater instability. Implications are important, affecting the optimal distance between rows of axial-flow turbines in array configurations: the operation at higher rotational speeds allows for smaller distances between turbines, decreasing the cost and environmental impact of farms consisting of several devices.

Roughness-Induced Transition in Supersonic Boundary Layers with Wall Heating and Cooling Effects

The laminar–turbulent transition of a supersonic boundary layer induced by an isolated roughness element is investigated using direct numerical simulation, BiGlobal linear stability theory, and the three-dimensional parabolized stability equation. Cylindrical and diamond-shaped roughness elements are investigated in combination with different wall temperatures. Direct numerical simulations show that the cylinder configuration induces an earlier transition than the diamond configuration, with the interaction between the separated shear layer and the counter-rotating vortices causing the transition. BiGlobal analysis and the parabolized stability equation confirm the existence of two unstable instability modes in the wake region, namely, a symmetric mode and an antisymmetric mode, with the former being strongly dominant. The wall cooling and heating effects are studied by changing the wall temperature. Wall heating lifts the inlet boundary layer and weakens the separated shear layer. This, in turn, weakens the wake instability and delays the transition. The antisymmetric model disappears as the wall heating increases. Wall cooling accelerates the transition by enhancing the distortion of the roughness wake, resulting in stronger instabilities. Finally, the Reynolds number based on the momentum defect is used to define the transition criterion, and this is found to be in good agreement with the present simulation results.

Numerical simulations of the Oldroyd-B fluid flow around triangular cylinders with different orientations

This study numerically simulates the two-dimensional flow of Oldroyd-B fluid around an isosceles right-angled triangular cylinder with five orientations. The log-conformation reformulation is employed to stabilize the numerical simulations. By adjusting the triangular orientation angle (θ), three types of fluids development process can be observed: from steady to vortex shedding at θ=0 and π, keeping the vortex shedding at θ=π4 and 3π4, and from vortex shedding to steady state at θ=π2. When the triangular cylinder faces the incoming stream with the inclined plane, the elastic effect acting on the cylinder is strong, otherwise it is weak. For θ=π2, the effects of the viscosity ratio (β), the Reynolds number (Re), and the Weissenberg number (Wi) are further investigated. When the elasticity is reduced by changing the viscosity ratio (β) that ranged from 0 to 0.9, the final flow state will transition from stable to vortex shedding state, which indicates the restraining effect of elasticity on wake instability. In the high elastic Oldroyd-B fluid, the critical Reynolds number for vortex shedding is about 110 for Wi=1. Besides, the Weissenberg numbers (Wi) ranged from 0.25 to 8 are discussed at Re=100. With the increase of Wi, four different flow states of the wake are observed: periodic vortex shedding at low Weissenberg number Wi=0.25, stabilizing for Wi ranged from 0.5 to 1, semi-periodic strong vortex shedding for Wi is about 2, and chaos when Wi≥4. The results indicate that excessively strong elastic effects may also lead to unstable flows. Finally, the flow states corresponding to each Reynolds number and Weissenberg number in a certain range (90≤Re≤120 and 0.125≤Wi≤4) are given in this study.

Fluid-Dynamic Mechanisms Underlying Wind Turbine Wake Control with Strouhal-Timed Actuation

A reduction in wake effects in large wind farms through wake-aware control has considerable potential to improve farm efficiency. This work examines the success of several emerging, empirically derived control methods that modify wind turbine wakes (i.e., the pulse method, helix method, and related methods) based on Strouhal numbers on the O(0.3). Drawing on previous work in the literature for jet and bluff-body flows, the analyses leverage the normal-mode representation of wake instabilities to characterize the large-scale wake meandering observed in actuated wakes. Idealized large-eddy simulations (LES) using an actuator-line representation of the turbine blades indicate that the n=0 and ±1 modes, which correspond to the pulse and helix forcing strategies, respectively, have faster initial growth rates than higher-order modes, suggesting these lower-order modes are more appropriate for wake control. Exciting these lower-order modes with periodic pitching of the blades produces increased modal growth, higher entrainment into the wake, and faster wake recovery. Modal energy gain and the entrainment rate both increase with streamwise distance from the rotor until the intermediate wake. This suggests that the wake meandering dynamics, which share close ties with the relatively well-characterized meandering dynamics in jet and bluff-body flows, are an essential component of the success of wind turbine wake control methods. A spatial linear stability analysis is also performed on the wake flows and yields insights on the modal evolution. In the context of the normal-mode representation of wake instabilities, these findings represent the first literature examining the characteristics of the wake meandering stemming from intentional Strouhal-timed wake actuation, and they help guide the ongoing work to understand the fluid-dynamic origins of the success of the pulse, helix, and related methods.

Predicting the upper bound of two-dimensional flow regimes of symmetric objects through two-dimensional computations

The onset of secondary wake instability is generally predicted via experiments, linear stability analysis, and three-dimensional direct numerical simulations. The current work stems from an open question that is very intriguing and fundamental: Can the upper bound of a two-dimensional flow be predicted purely on the basis of two-dimensional computational results? It is found that spatial distribution of a field variable, i.e., streamwise velocity in the vortex formation region, aids in determining the upper limit of a two-dimensional flow regime of a symmetric object. The vortex formation length attains its least value at the second critical Reynolds number. In addition, streamwise extents of mean wake and vortex formation region along wake axis become the same. Under this circumstance, the streamwise velocity at the terminal point of vortex formation region is such that its mean value vanishes while intensity of fluctuations or corresponding Reynolds stress becomes the maximum. The predicted values of critical Reynolds numbers for circular, square, and diamond cross sections exhibit excellent agreement with the results available in the literature.

Revealing the mechanism and scaling laws behind equilibrium altitudes of near-ground pitching hydrofoils

A classic lift decomposition (Von Kármán & Sears, J. Aeronaut. Sci., vol. 5, 1938, pp. 379–390) is conducted on potential flow simulations of a near-ground pitching hydrofoil. It is discovered that previously observed stable and unstable equilibrium altitudes are generated by a balance between positive wake-induced lift and negative quasi-steady lift while the added mass lift does not play a role. Using both simulations and experiments, detailed analyses of each lift component's near-ground behaviour provide further physical insights. When applied to three-dimensional pitching hydrofoils the lift decomposition reveals that the disappearance of equilibrium altitudes for ${A{\kern-4pt}R}\ {\rm (aspect\ ratio)} <1.5$ occurs due to the magnitude of the quasi-steady lift outweighing the magnitude of the wake-induced lift at all ground distances. Scaling laws for the quasi-steady lift, wake-induced lift and the stable equilibrium altitude are discovered. A simple scaling law for the lift of a steady foil in ground effect is derived. This scaling shows that both circulation enhancement and the velocity induced at a foil's leading edge by the bound vortex of its ground image foil are the essential physics to understand steady ground effect. The scaling laws for unsteady pitching foils can predict the equilibrium altitude to within $20\,\%$ of its value when $St\ {\rm (Strouhal\ number)} < 0.45$ . For $St \ge 0.45$ there is a wake instability effect, not accounted for in the scaling relations, that significantly alters the wake-induced lift. These results not only provide key physical insights and scaling laws for steady and unsteady ground effects, but also for two schooling hydrofoils in a side-by-side formation with an out-of-phase synchronization.

Passive Poststall Flow Control on Nonslender Delta Wings Using Flags

The lift force on two nonslender delta wings with sweep angles of Λ=40 and 50°, with flags attached to the leading edge, was investigated. Substantial lift enhancement in the poststall regime of the clean wings and the stall delay were observed. With a flag, the flowfield measurements showed the reattachment of the shear layer onto the wing surface and the re-formation of the leading-edge vortex, whereas the clean wing had completely stalled flow at the same angle of attack. Over a wide range of angles of attack, mass ratios, and flag lengths, the maximum lift enhancement was attained when the dimensionless frequency of flag oscillations was in an optimal range and the flag-tip velocity had sufficient amplitude. The optimal dimensionless frequency range corresponded to the natural shear layer instabilities of the clean wing. The excitation in this range substantially increased the coherency of the separated flow due to the flag oscillations. The main mechanism of the lift increase is the excitation of the shear layer, which exhibits convective instability. This is very different from the lift enhancement mechanism on airfoils where the flags lock-in to the wake instability, which is known to have an absolute instability at the poststall angles of attack of the clean airfoil.

Comparative study on the wake dynamics of pump-jet and ducted propeller based on dynamic mode decomposition

A comparative study on the wake dynamics of a pump-jet propulsor (PJP) and a ducted propeller (DP) is conducted to investigate the effects of the pre-swirl stator and corresponding stator–rotor interaction on the wake evolution and destabilization mechanisms of a PJP system. The flow field analysis, vortex structure identification, and dynamic mode decomposition (DMD) analysis are carried out based on the numerical results obtained from delayed detached eddy simulations. The numerical hydrodynamic loading and flow field of the PJP are compared with experimental results, and they are in good agreement. Compared with the DP, the stator trailing vortices of the PJP interact with the rotor trailing vortices as well as the hub vortex, accelerating their diffusion and viscous dissipation. The pre-swirl stator triggers the generation of secondary vortices and moderates the spiral behavior of tip leakage vortices, which dominates the wake instability of PJP. The DMD analysis revealed that the wake field evolution is primarily characterized by the different mode structures at blade passing frequency and its multiples, especially in the PJP due to its strong stator–rotor interaction. The modal energy decays faster in the PJP wake field owing to its more turbulent and earlier instability. The hub vortex plays an important role in the wake dynamics of the DP.

Association of Chrononutrition Indices with Anthropometric Parameters, Academic Performance, and Psychoemotional State of Adolescents: A Cross-Sectional Study.

Adolescents are an at-risk group for circadian misalignment. The contribution of sleep-wake rhythm instability to the psychoemotional, cognitive, and weight disorders of adolescents has been studied in sufficient detail. At the same time, there is insufficient information about the association between chrononutrition indices and the well-being of adolescents. The aim of this study is to investigate the relationship between chrononutrition indices and academic achievement, psychoemotional state, and anthropometric indicators in adolescents. The study involved 12,759 students in grades 6-11 of secondary schools, aged 14.2 ± 1.7 years old; 57.2% of whom were girls. Participants provided personal data, frequency and time of meals during the day and at night, on weekdays and weekends, and completed the Zung Self-Rating Depression Scale and the Yale Food Addiction Scale. There is a U-shaped association between eating mid-phase (EPFc), eating jetlag (EJL), and eating window (EW) with GPA, ZSDSI, and FA. At the same time, the frequency of night eating (NE) is linearly associated with the studied parameters. NE is the strongest predictor of ZSDSI (β = 0.24), FA (β = 0.04), and GPA (β = -0.22). EPFc, EJL, and EW practically do not differ in the strength of their association with the studied indicators. ZSDSI is most closely associated with the chrononutrition indices. There is a weak negative association between BMI and EW (β = -0.03) and NE (β = -0.04). Thus, circadian eating disorders are more often observed in adolescents with poor academic performance, high levels of depression, and food addiction.

Post-stall flow control on aerofoils by leading-edge flags

Self-excited oscillations of flags attached at the leading edge of aerofoils have been investigated at post-stall angles of attack at a chord Reynolds number of 100 000. Significant increases in the time-averaged lift coefficient and stall angle have been observed for three aerofoils: one symmetric, one cambered and one with a sharp leading edge. The aerodynamic improvement is due to the periodic formation of vortices caused by the flag oscillations. When the flag is near the aerofoil surface, it is lifted upwards by the induced velocity of the growing vortex. As the flag moves up, the vortex grows in strength and reaches maximum circulation when the flag is furthest from the aerofoil surface and subsequently sheds. Flags with large stiffness exhibit better spatial and temporal coherence of flag oscillations than the compliant flags, resulting in a larger maximum lift coefficient and higher stall angle. For all aerofoils tested, the best lift enhancement with respect to the clean aerofoils is found when the angle of attack is 6° to 10° above the stall angle of the clean aerofoil. High lift is observed when the flags are locked in with the wake instability in a narrow frequency band, depending on the flag mass ratio and length.

Effect of crossflow oscillation Strouhal number on circular cylinder wake

The wake flow features and aerodynamic characteristics of a circular cylinder in an oscillating crossflow were experimentally investigated. The study focused on crossflow oscillation Strouhal numbers that were smaller than the natural wake vortex-shedding Strouhal numbers. Crossflow oscillations were generated using a downstream rotating plate method. The flow evolution processes were observed using laser-light sheet assisted smoke flow visualization technique. Wake instability and time-averaged velocities were assessed using a one-component hot-wire anemometer and particle image velocimetry. Pressure distributions on the cylinder's surface were quantified using a linear pressure scanner, obtaining pressure coefficient distributions and drag forces. The wake instability Strouhal number, velocity vectors, streamline patterns, and recirculation bubble geometries in the wake region of the circular cylinder were determined. The wake turbulence properties were analyzed using the triple-decomposition method, including turbulence intensities and Lagrangian integral length and time scales. The results of natural and oscillating crossflows were compared. The wake vortex-shedding Strouhal number was lower than the natural Strouhal number but higher than the crossflow oscillation Strouhal number. It was primarily influenced by the oscillation Strouhal number and the Reynolds number of the crossflow. Critical crossflow Reynolds and oscillation Strouhal numbers were identified, beyond which the wake vortex-shedding Strouhal number reached a constant value. The crossflow oscillation intensity did not significantly affect the wake vortex-shedding behavior. The study provided quantitative descriptions and discussions of recirculation bubble geometries and statistical turbulence properties. Furthermore, the crossflow oscillations led to a substantial reduction in the drag coefficient experienced by the circular cylinder.

The dynamic characteristics in the wake systems of a propeller operating under different loading conditions

Improved delayed detached-eddy simulations (IDDES) on the computational domain composed of 48 million cells were employed to numerically simulate the propeller wake with various advance coefficients, shedding light on the dynamic characteristics and the evolution mechanisms for the entire wake system subject to different loading conditions. Validation against available experimental data under open water configuration was conducted to verify the numerical modelling in the present work. Dynamic mode decomposition, or to be more specific, its sparisity promoting varient, was further adopted to capture the fundamental spatio-temporal scales of the propeller wakes. The results of the simulation revealed that the low streamwise convection velocity with the high advance coefficient suppresses the wake vortex transportation, resulting in a helicoidal tip vortex system with strong interference effects and low pitch that leads to the earlier occurrence of propeller wake instability. The wake systems with high advance coefficient better maintain the memory of propeller rotation, resulting in more coherent downstream wakes. Moreover, the different interaction modes leading to wake instability were discussed.

On the onset of long-wavelength three-dimensional instability in the cylinder wake

We study the onset of the three-dimensional mode A instability in the near wake behind a circular cylinder. We show that long-wavelength perturbations organise in a time-shifting pattern such that the in-plane velocity in each streamwise slice corresponds to the base flow solution at shifted times. This observation introduces an additional unifying characteristic for certain mode A type instabilities. We then analyse the mechanisms which control the growth or decay of these perturbations and highlight the crucial role played by the tilting mechanism which operates via non-local interactions in a manner similar to Biot–Savart induction. We characterise its domain of influence using a Green's function-based approach which allows us to rationalise the non-trivial dependence of the growth rate on the spanwise wavenumber. We connect this behaviour to the subtle balance between the local growth of the perturbations as they are swept along by the flow and the feedback on the perturbations that are generated during the next period of the time-periodic base flow. Finally, we discuss generalisations of our findings to other types of flows.

Vortex-induced vibration of an elastically mounted cylinder subject to planar inflow shear

We have numerically investigated the effect of planar inflow shear on the vortex-induced vibration of a three-dimensional circular cylinder mounted on elastic supports in streamwise and cross-stream directions. At a Reynolds number Re=300, the reduced velocity (U∗) is varied in the range U∗=2−12 for a fixed mass ratio m∗=2. The effect of inflow shear is brought about by varying the shear parameter βy=0,0.05,0.1. We have observed four distinct branches in the structural response curve: Initial Branch (IB), High Amplitude Branch-1 (HAB1), High Amplitude Branch-2 (HAB2), and Desynchronization Branch (DS). The response of the cylinder is locked in with the near wake during IB, HAB1, and HAB2, where the inline oscillation amplitude of the cylinder triggers for increasing βy. The cylinder oscillates with a tilt against the high-velocity side at larger βy for HAB1 and HAB2 responses. During IB response at βy=0, the near wake shows the formation of vortex filaments clustered through the spanwise extent. However, in the HAB1 and HAB2 regimes, the propagation of secondary instability yields random occurrences of vortex splits in the wake. Similar consequences of vortex splits are found at βy=0.1 for IB, HAB1, and HAB2 regimes, where we observe fragmented vortex filaments wrapping around the vortex rings. For βy=0, we have found mode B-type wake instability in the IB response at a plane x=2, where the vortex structures form a staggered array with a spatial periodicity λ≈D. At z=0 plane, the vortex shedding mode is “2S” for the IB response at βy=0.05, while the “P+S” mode is at βy=0.1. The vortex strands experience stretching in the DS branch, where no specific shedding mode is discerned. The cross-stream evolution of time-averaged streamwise velocity shows a data collapse with an asymmetric localization above the cylinder for increasing βy. The streamwise and spanwise velocity fluctuations at βy=0.1 are insignificant compared to the cross-stream. However, for the IB and DS regimes, the growth of the rms velocities reveals spanwise invariance. In contrast, we found small-scale fluctuations of cross-stream velocities about the mean in the HAB1 regime. The temporal growth of the sectional drag coefficients (CDs) along the span shows a negative value in the IB regime for βy=0,0.5. However, we observe the quasiperiodic behavior of CDs along the span for the HAB1 regime at βy=0. The spanwise growth of CDs for the DS regimes shows intermittent transitions via the positive, zero, and negative values for different βy. For both IB and DS regimes at βy=0, the time evolution of sectional lift coefficients (CLs) is asymmetric along the span and represents a helical pattern. However, for increasing βy, the growth of CLs for HAB1 and HAB2 regimes is intermittent. An increase in βy triggers the magnitudes of CLs in the DS branch, where the spanwise evolution shows symmetric periodic bands of sectional lift coefficients.