Spanwise Vortices Research Articles

Numerical study of flow separation control over a circular hump using synthetic jet actuators

This study deals with the wall resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation of boundary layer flow separation over a circular hump model and its active control. An array of Synthetic Jet Actuators (SJAs) is implemented in the hump model to introduce a train of vortex rings into the boundary layer to control flow separation. The OpenFOAM solver is used to numerically simulate and analyze the fluid flow using the k–ω shear stress transport model. Hot wire anemometry and particle image velocimetry measurements are carried out to evaluate the accuracy of the URANS technique as well as the effectiveness of SJAs by comparing numerical predictions to experimental data. The time-averaged results are in a good agreement with experimental results and demonstrate a successful application of SJAs to delay the flow separation by the interactions of vortical structures with the separated shear flow. The three-dimensional simulation also reveals that near wall coherent flow structures (streamwise and spanwise vortices) are responsible for the wall shear stress components. The results can be used to better understand the performance of SJAs and to further improve future actuator configurations.

Coherent structures and mixing enhancement in a confined impinging-jet mixer

This study attempted to apply improved delayed detached-eddy simulation (IDDES) method to the prediction of the turbulent mixing in a confined impinging-jet mixer (a simplified model of a side-dump combustor). It was found that the time-averaged velocity and second-order statistics were in good agreement with available experimental data, demonstrating the reliability of IDDES for the numerical study of impinging jets. We visualized all discovered coherent structures and revealed the existence of two arrays of quasi-two-dimensional spanwise vortices in the jet shear layers and the continuous rolling-up of large-scale counter-rotating spanwise vortices in the downstream region with the aid of conditional sampling method. We provided insights on the generation and evolution mechanisms of both discovered and newly-discovered coherent structures. Furthermore, the effects of coherent structures on phase-averaged turbulence statistics were evaluated. The improvements of mixing efficiency associated with coherent structures were elaborated through the phase-averaging analysis on heat flux components.

Three-Dimensional Direct Numerical Simulations of a Yawed Square Cylinder in Steady Flow

The effects of yaw angle on wake characteristics of a stationary square cylinder were investigated in terms of the hydrodynamic forces, the vortex shedding frequency, and the vortical structures using direct numerical simulations (DNS) at a Reynolds number of 1000. In total, four yaw angles, namely, α = 0°, 15°, 30°, and 45°, were considered. The three-dimensional (3D) Navier–Stokes equations were solved directly using the finite volume method in OpenFOAM. It was found that the first-order statistics of the drag coefficient and the Strouhal number satisfied the independence principle (IP) closely. However, the second-order statistics of the drag and lift coefficients deviated apparently from the IP for α ≥ 25°. The iso-surfaces of the spanwise vorticity gradually disorganized and the magnitudes of the spanwise vorticity contour decreased as the yaw angle α was increased from 0° to 45°. By contrast, the streamwise vorticity iso-surfaces were found to become more organized and the magnitudes of the spanwise velocity contour became larger as a result of the increase in yaw angle, indicating the impairment of the quasi-two-dimensionality and the enhancement of the three-dimensionality of the wake flow. Extensive comparisons were also made with previous DNS results for a yawed circular cylinder, and both similarities and differences between these two kinds of cylinder wakes are discussed.

Effect of the bionic blade on the flow field of a straight-bladed vertical axis wind turbine

This paper uses the Particle Image Velocimetry technique through wind tunnel experiments to investigate the spanwise velocity and vortex characteristics of a straight-bladed vertical axis wind turbine (VAWT) and to verify the reliability of the numerical simulation model. The aerodynamic forces are obtained by a multiport pressure measurement device. To assess the flow field of VAWT with bionic blades, this paper compares results between numerical simulations and experiments. Different flow field characteristics of wind turbines have been found in the baseline blades and bionic blades. The research shows that the bionic blade can suppress the influence of the tip vortex on the velocity of the cross-section z/(H/2) = 1.0, and the wake recovery velocity of VAWT with bionic blades is lower than that with baseline blades. By comparing the tangential force coefficients of the blades, it has been found that the tangential force of the bionic blades increases in azimuth angle regions 30°<θ < 116° and 193°<θ < 301°. It has also been proven that the aerodynamic performance of the bionic blade is slightly better than the baseline blades at TSR = 2.19. This study provides a better understanding of the development of aerodynamic forces and vortex characteristics through torque and velocity measurements.

Vortex Dislocation In The Near Wake Of A Cylinder With Span-Wise Variations In Diameter

We examined the evolution of three-dimensional vortex shedding patterns induced by spanwise variations of the cylinder diameter. Two distinct types of shedding patterns have identified through flow visualization: continuous (in-phase) oblique shedding where vortices shed with lower frequency stay attached to the vortices with higher frequency without any discontinuity or splitting and discontinuous (out-of-phase) shedding where the lower frequency vortices have no attachment to higher frequency vortices and vortex dislocation occurs. The dislocation seen in the flow is strongly influenced by the span wise irregularities. We observed a clear and strong in-phase spanwise vortex shedding for the three smooth cylinder configurations tested in the study. The tapered, bumps and steps configurations showed sections of strong coherent spanwise vortex shedding, and we identified hardly any coherent structures for the rib, sinusoidal, and helical configurations. Depending on the geometry and number of span wise irregularities, incoherent structures make difficult to determine the occurrence and location of vortex dislocations in the cylinder wake without a method that enables a reduction in the complexity. Here, we introduce a numerical approach that obtains the dominant structures of vortex shedding patterns by reducing the complexity in noisy data. The method maps the variations in the oblique shedding angle over time and provide quantitative conclusions on the intermittent occurrence and location of vortex dislocations in the 15000 snapshots taken for each of the different cylinder geometries regardless of turbulence.

Indirect physical mechanism of viscous forces: Vortex stretching and twisting

In this paper, the indirect physical mechanism of viscous forces, i.e., vortex stretching and twisting, is theoretically explored. The local flow in the immediate neighborhood of a flat plate is analyzed. Only the viscous forces are considered. By introducing oppositely signed streamwise vorticity in such a region, the induced velocity and vorticity fields are obtained. Because the induced streamwise velocity varies along with both the wall-normal and spanwise directions, induced vertical and spanwise vorticities are generated. The induction sequence is first clarified. Then, two indirect effects of viscous forces are identified. The induced spanwise vorticity leads to the original two-dimensional spanwise vorticity increasing and decreasing alternately across the span, as the vortex stretching effect of viscous forces. The local spanwise vortex is distorted at positions where the streamwise vorticity is introduced, and the appearance of induced vertical vorticity at the same positions enhances this effect, as the vortex twisting effect of viscous forces.

Effect of yaw angle on vibration mode transition and wake structure of a near-wall flexible cylinder

The multi-mode transition and vortex structures in the vortex-induced vibration (VIV) of a near-wall flexible cylinder under different yaw angles are investigated through three-dimensional direct numerical simulation. Yaw angles α = 0°–60°, gap ratio G/D = 0.8, and Re = 500 are adopted. With the increase in α, the dominated vibration mode decreases from the 6th to 1st mode in the in-line (IL) direction and the 3rd to 2nd mode in the cross-flow (CF) direction. For the IL vibration, no mode transition occurs at α = 0°, whereas frequently mode transition is observed at α &amp;gt; 0°, due to the intermittent participation and spanwise competition of different modes, thus showing an intensified traveling-wave characteristic. For the CF vibration, mode transition is not excited at any α case even with spanwise mode competitions, due to the significant weight of the dominated mode, thus showing a strong standing-wave characteristic. The asymmetrical distributions of vibration displacements and force coefficients are established because of irregular energy transfer along the span. The spanwise vortex tubes at α = 0°–30° are separated into several cells associated with the dominated vibration mode, showing a locally parallel vortex shedding. However, positively yawed and negatively yawed vortex shedding are observed at α = 45° and 60°, respectively. The vortex strengths vary along the cylinder, where large-scale and small-scale vortices are observed at the CF anti-node and node planes, respectively. The independence principle is only valid at α &amp;lt; 15° for predicting the multi-mode vibrations and hydrodynamics, significantly reduced from that of α &amp;lt; 45° in the wall-free case or the mono-mode VIV case.

Helicity budget in turbulent channel flows with streamwise rotation

The streamwise rotation effects in turbulent channel flows are reflected not only in the appearance of the secondary flows but also in the weakened streamwise velocity and spanwise vorticity. In this paper, we investigate the secondary flows from three perspectives: the mean spanwise velocity, the mean streamwise vorticity, and combined mean and fluctuating helicity. We found that the combined helicity is also an alternative perspective to characterize the streamwise rotation effect, especially for the secondary flows. The budget equations of the mean and fluctuating helicity in physical space are derived theoretically and analyzed numerically. The streamwise rotation effects on the secondary flows are directly reflected on the pressure and Coriolis terms, which provides an essential source for helicity within the near-wall regions. The production term could be decomposed into two terms, which originate from the momentum and vorticity equations, respectively. The helical stress (velocity–vorticity correlation) originating from the vorticity equation shows a simple profile distribution and is dominant for the production for the helicity within the near-wall regions. The high helical structures in the core regions can be explained as an intense wall-normal transportation, which transfers produced helicity within the near-wall regions into the core regions.

Structure of turbulence in planar rough Couette flows

On roughening one of the walls in a planar Couette flow, it was reported that turbulence augments near the opposite wall [Javanappa and Narasimhamurthy, “Turbulent plane Couette flow with a roughened wall,” Phys. Rev. Fluids 6, 104609 (2021)]. The current direct numerical simulation work further explores this interesting phenomenon by investigating the flow dynamics and anisotropic nature of turbulence. For roughening, transverse square ribs are placed only on the bottom wall with streamwise pitch separations s=5r and 10r, where r=0.2h is the rib height and h is the channel half height. The time series of spanwise vorticity fluctuation in the case of s=10r shows the presence of coherent Kelvin–Helmholtz-like structures behind the ribs. Phase analysis using Hilbert transform reveals that the flow within the cavity for the s=5r case is in-phase, while a phase shift is observed for the s=10r case. The visualization of enstrophy production rate (ωiSijωj) reveals that regions of intense positive ones are observed to be topologically “sheet-like,” while the regions of negative ones are found to be “spotty.” Anisotropy tensors and anisotropic invariant maps are used to explore turbulence anisotropy at both large and small scales of motion. It is observed that anisotropy is reduced in both the cases near the vicinity of roughness.

Nonflat-Plate Transition-Serrated Trailing Edge for Airfoil Self-Noise Reduction

Trailing-edge noise is the primary source of airfoil self-noise. Nonflat-plate serrated trailing edge can suppress the broadband trailing-edge noise at high frequencies, while the overall noise reduction is compromised by low-frequency narrowband bluntness-induced noise at the sawtooth root. In this paper, a nonflat-plate transition-serrated trailing edge is proposed to reduce the bluntness-induced noise. The configuration uses a wedge-shaped transition structure within the sawtooth gap to eliminate the bluntness noise. Firstly, the appropriate parameters of the transition structure are determined by numerical simulation. Then, optimal configuration is employed for test verification. Finally, the noise reduction mechanism of the configuration with the best noise reduction is analyzed. Simulation results indicate that the configuration can accelerate the fragmentation of large-scale spanwise vortices at sawtooth root, weakening the vortex shedding noise. Moreover, compared with the nonflat-plate serrated trailing edge, it forms counter-rotating oblique vortices at a position further forward within the sawtooth gap, promoting transverse flow, thereby reducing broadband noise over most frequencies. Experimental results show that the configuration with an appropriate transition structure can afford the highest reduction of 27.2 dB for the bluntness-induced noise and 5.7 dB for the trailing-edge noise.

A comparative study on post-stall flow separation control mechanism of steady and unsteady plasma actuators

In order to improve the aerodynamic performance of the wing at post-stall conditions, the experimental comparative investigations on the flow separation control over an ONERA 212 airfoil using steady and unsteady plasma actuators are carried out at Reynolds number of 3.1 × 105. The duty cycle ratio is fixed at 80%, and the non-dimensional unsteady frequency F+ is varied from 0.04 to 1. The lift coefficients are increased by 39.6% and 66%, respectively, after steady and unsteady operations (F+ = 0.08) at an angle of attack of 18°, which indicates that the unsteady actuation is more efficient than steady operation. Meanwhile, the study provides new insight into understanding the post-stall separation flow controlling mechanism. First, different from the general view that the injection of momentum is the controlling mechanism of steady operation, flow control using the steady actuation experiences four stages, namely, flow separation, promoting the instability of the separated shear layer to produce large-scale spanwise vortices, flow re-attachment, and the continuous generation of small-scale vortices in the separated shear layer. Second, flow control with the unsteady operation consists of several quasi-periodic flow processes. Each quasi-cycle is composed of three stages, namely, flow separation, promoting the separation of shear layer instability to produce large-scale spanwise vortices, and flow re-attachment. The off-time of the plasma actuator plays an important role in realizing the control effect of the unsteady actuation, and an effective strategy to promote the control effect of the unsteady operation is proposed based on the propagation time of the induced spanwise vortex.

Computational analysis of compressibility effect on flow field and aerodynamics at low Reynolds numbers

The flow around the wing of exploration aircraft flying in the very dilute Martian atmosphere experiences very specific low-Reynolds-number compressible flows. A fundamental understanding of compressibility effects, especially on a separation bubble, is an important issue in the aerodynamic wing design. We investigated the effect of compressibility on the laminar separation bubbles and aerodynamic properties of a blunt flat plate with a thickness of 5% of the chord length in unsteady two-dimensional laminar and large-eddy simulations at chord-based Reynolds numbers (Re) of 6100 and 11 000 in the Mach number (M) range from M = 0.1 to 0.8. In the incompressible flow below M = 0.2 at Re = 11 000, the separated shear layer rolled up due to the Kelvin–Helmholtz (KH) instability reattaches to the surface with turbulent transition and then forms a laminar separation bubble. In contrast, with increasing Mach number, the transition and reattachment are delayed, and the separation bubble is stretched. In particular, at M = 0.8, the rolled-up vortex is not distorted in the span direction and advects downstream with a strong spanwise two-dimensionality. This is due to the compressibility effect that suppresses the KH instability. On the other hand, at Re = 6100, the separated shear layer is stable without spanwise distortion even in the incompressible flow due to the stronger influence of viscous forces. With increasing Mach number, such stable separated shear layer reattaches without rolling up further downstream, and the Strouhal number of the vortex also gradually decreases. This leads that the large lift oscillation owing to periodic and two-dimensional spanwise vortex shedding is significantly suppressed with an increasing Mach number. This is also due to the weakening of the KH instability due to the compressibility effects. However, at Re = 11 000, the reattachment points move downstream more significantly with the increasing Mach number, indicating that the suppression of the KH instability due to the compressibility effect is more pronounced at Re = 11 000 than at Re = 6100. Consequently, the negative skin friction shear stress owing to the reverse flow inside the expanded separation bubble becomes relatively large, decreasing the total drag with the increasing Mach number.

Origin of enhanced skin friction at the onset of boundary-layer transition

Boundary-layer transition is accompanied by a significant increase in skin friction whose origin is rigorously explained using the stochastic Lagrangian formulation of the Navier–Stokes equations. This formulation permits the exact analysis of vorticity dynamics in individual realizations of a viscous incompressible fluid flow. The Lagrangian reconstruction formula for vorticity is here extended for the first time to Neumann boundary conditions (Lighthill source). We can thus express the wall vorticity, and, therefore, the wall stress, as the expectation of a stochastic Cauchy invariant in backward time, with contributions from (a) wall vorticity flux (Lighthill source) and (b) interior vorticity that has been evolved by nonlinear advection, viscous diffusion, vortex stretching and tilting. We consider the origin of stress maxima in the transitional region, examining a sufficient number of events to represent the increased skin friction. The stochastic Cauchy analysis is applied to each event to trace the origin of the wall vorticity. We find that the Lighthill source, vortex tilting, diffusion and advection of the outer vorticity make minor contributions. They are less important than spanwise stretching of near-wall spanwise vorticity, which is the dominant source of skin-friction increase during laminar-to-turbulent transition. Our analysis should assist more generally in understanding drag generation and reduction strategies and flow separation in terms of near-wall vorticity dynamics.

Three-dimensional direct numerical simulations of two interfering side-by-side circular cylinders at intermediate spacing ratios

Side-by-side arranged circular cylinders show fierce interferences when they are not far apart. In this paper, we present the vibration response and wake characteristics of two elastically mounted circular cylinders in a side-by-side arrangement through three-dimensional direct numerical simulations (3-D DNS). The Reynolds number is Re = 500 and two center-to-center spacings (s) of 2.0D and 2.5D are considered where D is the diameter of the two cylinders. We found that with the increasing reduced velocity, the responses of both s/D cases can be divided into three different regions, which are named desynchronization region (DS), initial branch (IB), and lower branch (LB), with the former being further divided into two subregions (DS-I and DS-II). The vibration, hydrodynamic forces, and spectral features in each region are discussed in detail. According to the characteristics of cylinder oscillation and vortex dynamics, six types of wake patterns are identified, with the deflected (DF) and flip-flopping (FF) patterns at s/D = 2.0 while in-phase (IP), anti-phase (AP), in-/anti-phase (I/AP), and hybrid (HB) patterns at both s/D = 2.0 and 2.5. Furthermore, we investigated the wake three-dimensionality through the evolution of vortical structures, and the statistics and development of the enstrophies. It was observed that the presence of the streamwise vortices modifies the strength and spanwise coherence of the spanwise vortices. Finally, flow physics for the interactions of the two cylinders at different regions is elucidated.

Structure of turbulence in temporal planar jets

A detailed analysis of the structure of turbulence in a temporal planar turbulent jet is reported. Instantaneous snapshots of the flow and three-dimensional spatial correlation functions are considered. It is found that the flow is characterized by large-scale spanwise vortices whose motion is felt in the entire flow field. Superimposed to this large-scale motion, a hierarchy of turbulent structures is present. The most coherent ones take the form of quasi-streamwise vortices and high and low streamwise velocity streaks. The topology of these interacting structures is analyzed by quantitatively addressing their shape and size in the different flow regions. Such information is recognized to be relevant for a structural description of the otherwise disorganized motion in turbulent free-shear flows and can be used for the assessment of models based on coherent structure assumptions. Finally, the resulting scenario provides a phenomenological description of the elementary processes at the basis of turbulence in free-shear flows.

Large-Eddy Simulation of the Boundary Layer Development in a Low-Pressure Turbine Cascade With Passive Flow Control

The boundary layer development on a low-pressure turbine blade surface modified by recessed dimples, U-grooves, and rectangular grooves has been investigated through the large-eddy simulations. The simulations are performed at a Reynolds number of 50,000 (based on the inlet velocity and axial chord length) and extremely low freestream turbulence conditions. The characteristic parameters of the boundary layer are used to estimate the development of the boundary layer, and spectral analysis has also been performed to identify the dominant frequency of shedding vortices. The results of simulations indicate that three surface modifications all reduce the profile losses by restraining the separation bubble size. However, the grooves and dimples show different mechanisms in inhibiting laminar separation. Grooves tend to promote the formation of spanwise vortices, which is more difficult to break into turbulence. A high-speed shedding vortex is induced by the particular 3D structure of dimple, and its shedding frequency is nearly twice the Kelvin–Helmholtz (K-H) instability frequency. The interaction between the shedding vortices and the K-H vortices promotes the breakdown process of the spanwise vortices, which leads to an earlier transition of the boundary layer at a low disturbance level. The current study reveals the different mechanisms of dimples and grooves and shows the great potential of dimples for flow control in low-pressure turbines. Besides, the flow structures inside the dimples with adverse pressure gradients are also explored.

Coherence of unsteady wake of periodically plunging airfoil

We present an experimental investigation of the flow structure in the near wake of a NACA0012 airfoil plunging sinusoidally at a chord Reynolds number of Re = 20 000 and for a wide range of reduced frequency k and Strouhal number based on peak-to-peak amplitude St. Estimated mean thrust coefficients using the mean and fluctuating velocity fields confirm the St2 dependence as well as a significant effect of the reduced frequency for k ≤ 1. Generally, time-averaged flow quantities are better correlated with St than k in the range tested (k ≤ 3.14 and St ≤ 0.24). Analysis of the streamwise flow and cross-flow in the near wake using two-point cross-correlations and proper orthogonal decomposition reveals that the unsteady characteristics are even better correlated with St than the mean flow quantities. The percentage energy of the fundamental wake modes of the streamwise flow and the flapping mode of the cross-flow increases with increasing St, but at different rates in the drag-producing and thrust-producing wakes. There are similarities to the wake synchronisation behind oscillating bodies. The spanwise-averaged cross-correlation coefficient in the measurement domain grows linearly for small St (in drag-producing wakes), and is nearly constant at a high value for larger St (in thrust-producing wakes). Results show that the Strouhal number is the most important parameter that determines the degree of two-dimensionality of the wake, and suggest that spanwise vortices are quasi-two-dimensional for St ≥ 0.05 and x/c ≤ 4. The implications for experimental gust generators using oscillating airfoils are discussed.

Flow control of wake around a wall-mounted cube using a horizontal hole of different diameters

This paper describes an experimental investigation of flow control for the wake around a wall-mounted cube using horizontal control holes (HCHs) of different diameters drilled from the center of the front surface to the rear surface of the cube. The cube has side lengths of D = 50 mm, and HCHs with diameters of d = 10, 12, and 14 mm are considered. The instantaneous velocity fields are measured at a Reynolds number of 7800 based on time-resolved particle image velocimetry in a water tunnel. The HCHs suppress the recirculation zone, turbulence intensity, and Reynolds stress, and these control effects gradually increase with the hole diameter. The issuing flow from the large-diameter HCH completely obstructs the development of the downwash flow to the bottom wall and decomposes the near-wake arch-type vortex into a double arch-type structure. As the hole diameter increases, the dominant frequency of the spectrum in the HCH wake increases. Proper orthogonal decomposition analysis indicates that the large-scale spanwise vortices are suppressed by HCH. In the dynamic evolution process of the cube wake, the HCH issuing flow hinders the interaction of shear flow on both sides, and the issuing vortices attract the spanwise vortices and accelerate their shedding.

An investigation of bluff body flow structures in variable velocity flows

The present study explores three-dimensional vortex-dynamics past a wall-attached bluff body kept in a variable velocity field with numerical simulations. A trapezoidal pulse of mean velocity, consisting of acceleration phase from rest followed by constant velocity phase and deceleration phase to rest, is imposed at the inlet of the computational domain similar to the experimental study of Das et al. [“Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body,” J. Fluids Struct. 40, 233–245 (2013)]. For a wide range of Reynolds numbers (96≤Reb≤2390), acceleration Reynolds numbers (196≤Rea≤978), and deceleration Reynolds numbers (310≤Red≤1522), different stages of flow evolution are systematically analyzed. The flow evolution starts with the formation of a primary vortex followed by a two-dimensional circular array of spanwise vortex tubes by inflectional shear-layer instability. At a sufficiently high Reynolds number, the shear layer vortices originated from two-dimensional fluctuations deformed by three-dimensional instabilities, giving fragmented streamwise vorticity. In addition, long-wavelength “tongue-like structures” and short-wavelength “rib-like structures” are evident near the top wall and the bluff body, respectively. The streamwise vorticity generation equation indicates that the spanwise vortex tubes initially tilt, resulting in streamwise vorticity, further amplified by the vortex stretching process. The distinct flow features, including mode shape, frequency, and growth rate associated with the shear-layer instability, are identified using the dynamic mode decomposition (DMD) algorithm. Using the maximum growth rate criteria, the DMD technique successfully separates the coherent shear layer modes associated with two-dimensional shear layer instability from the flow field.

Wake behind a discontinuous cylinder: unveiling the role of the large scales in wake growth and entrainment

The turbulent flow in the wake of a discontinuous cylinder (DC) was investigated. The DC geometry consisted of cylinder segments $5D$ long (with $D$ being the diameter of the cylinder) separated by gaps of width $2.5D$ . Particle image velocimetry and hot-wire anemometry were used to analyse the flow at two Reynolds numbers, $Re = 4000$ and $10\,000$ , for $x/D \le 180$ . Large eddy simulations for both the DC and the infinite continuous cylinder (CC) wakes were also carried out at $Re = 10\,000$ . The DC configuration was devised to trigger the shedding of horseshoe vortices (HSV) in the very-near-wake region with the intent of illustrating the role that these three-dimensional HSVs, previously identified in the far-wake region of CC, play in the entrainment process in turbulent wakes. The DC geometry produced HSVs by the interaction between the high momentum flow through the gaps and the main spanwise vortex shed behind each cylinder segment, while in the CC wake they evolve from near-wake instabilities straddled with hairpin vortices that detach spanwise vorticity from the shed Kármán vortices. The DC wake was found to grow and spread in the transverse direction with a much faster rate than for the CC wake, up until approximately $x/D \approx 50$ . Prior to this location, the enhanced growth rate caused by the shear-aligned HSV led to a wake width of approximately 3 times that of the CC wake, with a maximum mean velocity deficit that was approximately half.