Velocity Layer Research Articles

Effects of Reynolds number and blockage ratio on the turbulence characteristics of open channel flow passing through trash rack

Trash racks are extensively used to prevent debris from being transported to down-stream reaches of waterways. However, debris accumulation at the screens can significantly affect their hydraulic performance, resulting in negative economic and environmental consequences. Basic research related to the mechanism of these physical processes is still rather limited. In this experimental study, the flow fields, including the turbulence intensities, Reynolds stresses, and turbulent kinetic energy near a trash rack in a fixed-bed open channel for subcritical flow conditions are investigated for two Reynolds numbers and two blockage ratios. The experimental study investigates the important physical mechanisms relating to turbulence generation and possible sediment deposition induced by the vertical trash rack. Reynolds number effect on time mean streamwise velocity is predominant in the trash rack’s downstream free surface layer as a higher Reynolds number flow has higher normalized streamwise velocity in the free surface layer and lower in the inner layer. In both the Reynolds number effect case and the blockage ratio effect case peak normalized turbulent kinetic energy was observed immediately downstream of the trash rack and with the increment of longitudinal distance downstream of the trash rack, normalized Turbulent kinetic energy is decreased.

On the eigenvalues and eigendisplacement of the critical mode in horizontally layered media

Wave propagation in horizontally layered media is a classical problem in seismic-wave theory. In semi-infinite space, a nondispersive Rayleigh wave mode exists, and the eigendisplacement decays exponentially with depth. In a layered model with increasing layer velocity, the phase velocity of the Rayleigh wave varies between the S-wave velocity of the bottom half-space and that of the classical Rayleigh wave propagated in a supposed half-space formed by the parameters of the top layer. If the phase velocity is the same as the P- or S-wave velocity of the layer, which is called the critical mode or critical phase velocity of surface waves, the general solution of the wave equation is not a homogeneous (expressed by trigonometric functions) or inhomogeneous (expressed by exponential functions) plane wave, but one whose amplitude changes linearly with depth (expressed by a linear function). Theories based on a general solution containing only trigonometric or exponential functions do not apply to the critical mode, owing to the singularity at the critical phase velocity. In this study, based on the classical framework of generalized reflection and transmission coefficients, the propagation of surface waves in horizontally layered media was studied by introducing a solution for the linear function at the critical phase velocity. Therefore, the eigenvalues and eigenfunctions of the critical mode can be calculated by solving a singular problem. The eigendisplacement characteristics associated with the critical phase velocity were investigated for different layered models. In contrast to the normal mode, the eigendisplacement associated with the critical phase velocity exhibits different characteristics. If the phase velocity is equal to the S-wave velocity in the bottom half-space, the eigendisplacement remains constant with increasing depth.

Robot manipulator tracking control with conquering joint physical limits at angle and velocity layers based on different-layer equivalency technique

The study of manipulator physical limits is a very important direction in the field of robotics. Most traditional approaches to addressing physical limits are typically within the framework of optimization, treating physical limits as constraints to be addressed. However, this approach has a limitation in that it may not be real-time responsive. In order to improve real-time performance, latest study in literature formulated physical limits and tracking task as different-layer time-varying problems. This approach effectively enhances real-time performance via obtaining calculated control variables in advance. Nevertheless, this study only considers joint angle limits, without taking into account the higher-layer joint velocity limits. This work conquers physical limits at angle and velocity layers simultaneously by a three-layer time-varying system. Two different ways are used to solve the system based on different-layer equivalency technique, and two differential equations are obtained. The equations are discretized by using a discretization formula, and then two discrete models are proposed. The robot tracking control conquers physical limits at angle and velocity layers simultaneously by using discrete models. Theoretical convergence of the discrete models is demonstrated. Furthermore, the effectiveness and superiority of models are also verified through numerical experiments.

Oceanic crust—seismic structure, lithology and the cause of the 2A Event at borehole 504B

SUMMARY This study focuses on the 3-D velocity structure and thickness of ∼7-Myr-old oceanic crust surrounding borehole 504B, located ∼235 km from the intermediate-spreading Costa Rica Rift (Panama Basin). It investigates how well seismic structure determined by 3-D tomography compares with actual lithology and, consequently, what the origin and cause might be of an amplitude anomaly, the 2A Event, that is observed in multichannel seismic data. Our P-wave model shows an ∼0.3-km-thick sediment layer of velocity between ∼1.6 and 1.9 km s−1 (gradient 1.0 s−1), bound at its base by a velocity step to 4.8 km s−1 at the top of oceanic crustal Layer 2. Layer 2 itself is subdivided into two main units (2A and 2B) by a vertical velocity gradient change at 4.5 km depth, with a gradient of 1.7 s−1 above (4.8–5.8 km s−1) and 0.7 s−1 below (5.8–6.5 km s−1). The base of Layer 2, in turn, is defined by a change in gradient at 5.6 km depth. Below this, Layer 3 has a velocity range of 6.5–7.5 km s−1 and a gradient of ∼0.3 s−1. Corresponding S-wave igneous layer velocities and gradients are: Layer 2A, 2.4–3.1 km s−1 and 1.0 s−1; Layer 2B, 3.1–3.7 km s−1 and 0.5 s−1; Layer 3, 3.7–4.0 km s−1 and 0.1 s−1. The 3-D tomographic models, coupled with gravity modelling, indicate that the crust is ∼6 km thick throughout the region, with a generally flat-lying Moho. Although the P- and S-wave models are smooth, their velocities and gradients are remarkably consistent with the main lithological layering subdivisions logged within 504B. Thus, using the change in velocity gradient as a proxy, Layer 2 is interpreted as ∼1.8 km thick and Layer 3 as ∼3.8 km thick, with little vertical variation throughout the 3-D volume. However, the strike of lateral gradient variation is not Costa Rica Rift-parallel, but instead follows the orientation of the present-day adjacent Ecuador Rift, suggesting a reorientation of the Costa Rica Rift spreading ridge axis. Having determined its consistency with lithological ground-truth, the resulting P-wave model is used as the basis of finite difference calculation of wave propagation to find the origin of the 2A Event. Our modelling shows that no distinct interface, or transition, is required to generate this event. Instead, it is caused by averaging of heterogeneous physical properties by the seismic wave as it propagates through Layer 2 and is scattered. Thus, we conclude that the 2A Event originates and propagates exclusively in the lower part of Layer 2A, above the mean depth to the top of the dykes of Layer 2B. From our synthetic data we conclude that using the 2A Event on seismic reflection profiles as a proxy to determine the Layer 2A/2B boundary's depth will result in an overestimate of up to several hundred metres, the degree of which being dependent on the specific velocity chosen for normal moveout correction prior to stacking.

The structure of the mantle transition zone and its implications for mantle upwelling beneath the central Tibetan plateau from triplicated P-waveforms modeling

The Tibetan plateau is considered as an ideal place for studying the continental collisions, tectonic movements and regional geodynamics. Although multiple episodes of igneous activities in Tibetan plateau have been suggested derived from mantle upwelling, their origins and corresponding geodynamic models remain vigorously debate. This study presents a high-resolution upper mantle velocity model of P-wave and its lateral variation beneath the central Tibetan plateau based on triplicated waveform modeling. The results show that, compared with IASP91 model, the 660-km discontinuity is deepened approximately 17–28 km from the Qiangtang terrane to the Beishan block. The lower mantle transition zone (MTZ) is characterized by high P-wave velocity anomalies (HVA) in range of 0.3%–0.9%. We infer that they are mainly related to the hydrous materials with low temperature in the lower MTZ. Besides, the depression of the 410-km discontinuity is about 6–15 km. A remarkable low velocity layer (LVL) is detected atop the 410-km discontinuity, exhibiting the thickness of 31–40 km and low P-wave velocity anomaly of −2.5% to −1.6%. This is against completely temperature-dominated origin of the LVL, and suggests that the material composition has also contributes. Additionally, we propose a new geodynamic model to demonstrate the asthenospheric upwelling beneath the Qiangtang and Songpan-Ganzi terranes, which suggests that the passively ascending water-enriched materials from the lower MTZ and their dehydration are responsible for the observed LVL atop the 410-km discontinuity, as well as the origin of the Cenozoic magmatic intrusion and volcanic eruption of the northern Tibet volcano in Pleistocene.

A FEM Flow Impact Acoustic Model Applied to Rapid Computation of Ocean-Acoustic Remote Sensing in Mesoscale Eddy Seas

Mesoscale eddies have an impact on the marine environment mainly in two areas, namely, currents and changes in the sound velocity gradient due to temperature and salt stirring. The traditional underwater-related remote sensing acoustic remote sensing model is capable of analyzing the acoustic field under the change in sound velocity gradient, but it is not capable of analyzing the acoustic field under the influence of ocean currents. In order to more effectively analyze the changes in the acoustic field caused by mesoscale eddies, this paper proposes a FEM flow impact model applied to the rapid computation of acoustic remote sensing of mesoscale eddies in the sea area. The algorithm first performs a grid optimization of the sea area model based on vertical sound velocity variations and completes the classification of sound velocity layer junctions. At the same time, we construct the sound velocity gradient environment affected by the mesoscale eddy and then simplify the fluid flow in the mesoscale eddy into a non-viscous and non-rotating velocity potential, and then participate in the solution of the three-dimensional spatial fluctuation equations in the form of time-harmonic in the frequency domain, from which we can obtain the truncated sound pressure as well as the propagation loss, and quickly and completely characterize the acoustic remote sensing of the sea area of the mesoscale eddy. The paper verifies the effectiveness of the algorithm through SW06-contained flow experiments and further proposes an optimization formula for sound velocity inversion. We analyze this using measured data of mesoscale eddy fields in the Bering Sea waters during 2022 and find that eddies have a greater effect on the propagation of the acoustic field along their flow direction.

Wind waves impact on the velocity in wave boundary layer in the condition of dynamically smooth surface

One of the factors of wind wave impact on vertical distributions in atmosphere surface layer is the flux of momentum produced by the wave-produced fluctuations. Wave surface are supposed to be a dynamically rough and effects of the molecular viscosity are neglected. In this paper impact of wave momentum fluxes with values of wind velocity which lead to dynamically smooth ocean surface is estimated. The well-known theoretical aspects and results of experimental research are applied. Dependence of dimensionless thickness of viscosity layer on dimensionless roughness of smooth surface is analyzed. The equations of motion are formed taking into account the manifestation of three factors: molecular, turbulent and wave momentum flux. The models based on these equations are described.The choice of constant coefficients that are set in calculations with this model is considered. Results of calculations and analysis of vertical profiles of wind speed and the dependence of the drag coefficient on wind velocity under various wave age.

Stall control on the wind turbine airfoil via the single and dual-channel of combining bowing and suction technique

Based on the single-channel jet control strategy with a suction slot on the upper surface and injection slots near the trailing edge on the lower surface, proposed in this work is a novel flow control technique, known as the dual-channel jet, which amalgamates the beneficial aspects of leading-edge suction and a suction slot positioned downstream of the airfoil's maximum thickness position. To demonstrate the superior aerodynamic characteristics of the dual-channel over the single-channel, comprehensive comparisons of three distinct control strategies are made with two jet momentum coefficients employed on the S809 airfoils. Simulations using Reynolds-averaged Navier-Stokes with a transitional SST turbulence model are performed, showing that the position of a suction slot in the single-channel significantly impacts its ability to inhibit separation, while the dual-channel jet facilitates a fuller boundary layer velocity profile and a posterior shift in the stagnation point, outperforming the single-channel approach in removing low-momentum fluid and increasing the airfoil virtual camber. In the case with a jet strength of 0.004 and pitching oscillation, compared to the clean airfoil, the dual-channel achieves a remarkable 84.21 % increase in the lift coefficient at 18.1°, and the control efficiency can further be enhanced with the momentum coefficient increased.

Complexity analysis of two-point velocity in the relaminarizing turbulent boundary layer

Complexity analysis of two-point velocity in the relaminarizing turbulent boundary layer

Development of Nonlinear Site Amplification Model Based on Average Shear-wave Velocity of Soil Layer and Bedrock Depth

Development of Nonlinear Site Amplification Model Based on Average Shear-wave Velocity of Soil Layer and Bedrock Depth

IMPACT OF POROUS AND MAGNETIC DISSIPATION ON DISSIPATIVE FLUID FLOW AND HEAT TRANSFER IN THE PRESENCE OF DARCY-BRINKMAN POROUS MEDIUM

In this article, the boundary layer flow of an electrically-conducting fluid through a porous medium attached with a radiative permeable stretching sheet is analyzed. Following the Brinkman theory, an extended Darcy model (Darcy-Brinkman model) is utilized for the model momentum equation. Heat transfer analysis is also performed in the presence of viscous and Joule dissipation. Moreover, in the modeling of the energy equation, the effects of internal heating resulting from the mechanical effort required to squeeze out the fluid through the porous medium are also included in porous dissipation. Suitable dimensionless variables are introduced to convert the governing boundary layer equations into a dimensionless form, which are then converted into self-similar, nonlinear ordinary differential equations by utilizing similarity transformations. The exact solution of the nonlinear self-similar momentum equation is obtained in the form of the exponential function. In contrast, the solution of the energy equation is computed through the Laplace transform technique in the form of Kummer confluent hypergeometric functions. Effects of involved physical parameters on the momentum boundary layer (MBL), thermal boundary layer (TBL), wall shear stress, and local Nusselt number are explored through graphs and tables. Moreover, the slope linear regression (SLR) technique is used to calculate the rate of decrease/increase in shear stress and the rate of heat transfer at the boundary. The velocity and momentum boundary layer decreases for large values of porosity parameter and increases by increasing the viscosity ratio. The shear stress increases by increasing the porosity parameter, Hartman number, and suction parameter, while the opposite effect is examined with increasing values of viscosity ratio parameter. Heat transfer rate also enhances by increasing the Brinkman viscosity ratio parameter and wall suction velocity.

A Study of Intermittent Turbulence in Stable Arctic Boundary Layers

Polar boundary layers are difficult to model due to the existence of intermittent turbulence within stable layers. Here we present a case study evaluation of coherent structures in a stable boundary layer observed during a series of flights with an uncrewed aircraft system (DataHawk2) on 19 October 2016 at Oliktok Point, Alaska as part of the ERASMUS (Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems) field campaign. During a sequence of five flights over a nine-hour period, 57 profiles of atmospheric properties (0–400 m a.g.l) were collected. Turbulence was identified using derived Richardson Number, temperature structure function parameter, and turbulence kinetic energy dissipation. Throughout all flights on this strongly stable day, intermittent turbulence was observed. These turbulent layers showed well-mixed potential temperature profiles embedded within otherwise stable potential temperature profiles; often resulting in a characteristic staircase pattern. Turbulent layers ranged from 1 to 30 m deep, with most individual layers being 1–2 m deep. Vertical propagation velocities of layers in the lower atmosphere were on the order of a few cm s−1, typical of non-convective environments. In different regions of the profile, turbulence was driven by a different balance of buoyancy and shear forces, with turbulence in the near surface environment driven by strong shear forces overcoming strong resistance to buoyancy, while turbulence in elevated layers characterized by weaker shear forces overcoming weaker resistance to buoyancy. We discuss the potential of such datasets for improving subgrid parameterizations of small-scale turbulence embedded within stable boundary layers.

The polymer melt swelling behavior in micro-extrusion process for preparation of continuous carbon fiber reinforced PP prepreg filament

The micro-extrusion process for polymer melt has been increasingly used for the production of high value-added prepreg filaments with applications in the fields of fused deposition modeling (FDM). In this study, the effect of characteristic scale, defined as the gap of die land in an annular micro-extrusion die, on the extrudate swelling behaviour of viscoelastic melt is analyzed through numerical simulations and micro-extrusion experiments. The results show that the swelling behaviour displays an obvious dependence on the characteristic scale. An increase in the characteristic scale reduces the swell ratio and retards the process to reach the equilibrium state. In contrast, a decrease in the characteristic scale results in a larger magnitude of change in velocity field and faster relaxation development of stress field. The location of the maximum velocity layer for the laminar flow gradually deviates from the geometric center of channel toward the wall of mandrel with the increase in the characteristic scale. It is imperative to consider the complicated swelling behavior and remarkable viscoelastic effect simultaneously in micro-extrusion process.

LDV measurements of boundary layer velocity profiles on flat plates with different surface roughnesses

The dynamics acting upon thin flat plates submerged in a fluid are chiefly governed by the delicate boundary layer enveloping their surfaces. Through a series of experiments, we investigated the impact of surface roughness elements on the boundary layer adjacent to a flat plate across a range of Reynolds numbers. The experiments were performed in the Chungnam National University-Cavitation Tunnel (CNU-CT). Three flat plates, each characterized by distinct surface roughness heights denoted by k, were subjected to scrutiny. One boasted a pristine smoothness, while the others bore the deliberate roughness of sandpaper, each with its own unique texture. With precision instrumentation, including Laser Doppler Velocimetry (LDV), we meticulously documented the axial velocity profile and the RMS (Root Mean Square) velocity at strategic points along the flat plates. Through these measurements, we unveiled the boundary layer's thickness, δ, and momentum thickness, θ, elucidating their variations under differing free-stream velocities. As our exploration deepened, the relationship between the local Reynolds number, Rnx, and the non-dimensional velocity profiles, u+ − y+, became apparent. A systematic shift along the log-law line ensued, with both u+ and y + increasing in tandem with the rise in Rnx. Yet, our inquiry did not conclude with observation alone. Employing empirical rigor, we quantified the drag forces acting upon flat plates of varying roughness heights, deriving them from the measured momentum thickness across a range of local Reynolds numbers, Rnx.

Numerical and Experimental Investigation of the Influence of Backpressure on a Confined Impinging Jet for Small Nozzle-to-plate Spacing

In order to further extend understanding of the heat transfer characteristics under an enclosed area, the influence of backpressure on a single impingement jet with small nozzle-to-plate spacing (H/D) is studied. Particle image velocimetry (PIV) technique and a commercial fluid dynamics solver (CFD) are respectively employed to investigate the fluid dynamics of the impinging jet, with a Reynolds number (Re) of 3462–6125, at a small nozzle-to-plate spacing (H/D) of 0.25–1.25. Experimental data are in well agreement with numerical simulation data. The findings indicate that the H/D ratio significantly influences the formation of backpressure in the flow field. The backpressure then influences the boundary layer velocity on the impingement surface, in turn affecting the impingement surface's heat transfer characteristics. In addition, a turning point in the horizontal velocity curve of H/D = 0.4 is found for an entire range of jet heights, which is independent of the Reynolds number (Re).

A new machine learning approach for estimating shear wave velocity profile using borelog data

The shear wave velocity is among the key parameters that are responsible for damage caused during an earthquake. Determining shear wave velocity is a costly and time-consuming direct geophysical method. In the present paper, a machine learning model has been developed to obtain the subsurface shear wave velocity profile without using direct methods. The bore log information and the subsurface shear wave velocity profile available at various stations of Japan’s Kyoshin network (K-NET) have been utilized for training this machine learning model. The parametric correlation study indicates that simple parameters like rock/soil type, the thickness of the layer in the model, and standard penetration test (SPT-N) value directly correlate with the medium’s shear wave velocity. A stacked ensemble machine learning model named VelProfES (an acronym for Velocity Profiler using Ensemble machine learning models) has been developed in this paper and has been utilized for effective prediction of the shear wave velocity profile using basic information from borelog data. The dataset used in the training and testing of the machine learning model consists of borelog and shear wave velocity information from 1101 stations. Of 1101 stations, 657, 283, and 71 stations have been utilized for training, testing, and validating the machine learning model. Training, testing, and validation of the developed machine learning model consist of parameters from 12351, 5279, and 1388 velocity layers. The problem of data imbalance based on soil type has been addressed using an additional 10510 layers of synthetic borelog data generated from conditional generative adversarial networks (CTGANs). A feature and model ablation study was conducted for the VelProfES model to provide substantiation for the model and feature selection choices. The predicted shear wave velocity profiles were compared at specific stations, focusing on average velocities at 5, 10, 15, and 20 depths. Further, the predicted values have been compared with the empirical relation of Sil and Haloi (2017) and a trained polynomial model. The machine learning model demonstrates close alignment between predicted and actual values across a broad spectrum of velocities, a contrast not observed in the empirical relation and polynomial model. The results show that the machine learning models and augmented data generated using CTGANs can efficiently minimize the error between actual and predicted subsurface shear wave velocity values.

Evidence for a Kilometer‐Scale Seismically Slow Layer Atop the Core‐Mantle Boundary From Normal Modes

AbstractGeodynamic modeling and seismic studies have highlighted the possibility that a thin layer of low seismic velocities, potentially molten, may sit atop the core‐mantle boundary but has thus far eluded detection. In this study we employ normal modes, an independent data type to body waves, to assess the visibility of a seismically slow layer atop the core‐mantle boundary to normal mode center frequencies. Using forward modeling and a data set of 353 normal mode observations we find that some center frequencies are sensitive to one‐dimensional kilometer‐scale structure at the core‐mantle boundary. Furthermore, a global slow and dense layer 1–3 km thick is better‐fitting than no layer. The well‐fitting parameter space is broad with a wide range of possible seismic parameters, which precludes inferring a possible composition or phase. Our methodology cannot uniquely detect a layer in the Earth but one should be considered possible and accounted for in future studies.

Design and performance of ultra-broadband composite meta-absorber in the 200Hz-20kHz range

In this study, a composite meta-absorber with a flexible size is proposed, and a genetic algorithm is used to optimize the geometric dimensions under normal incidence and free field conditions. With an overall thickness of 0.2 m, the quasi-perfect sound absorption is achieved in the 200 Hz - 20 kHz range. The sound pressure and sound intensity distributions inside the composite meta-absorber prove the incident sound wave is effectively localized inside the structure. Comparing the effective sound velocities in layers 1 and 10 with the sound velocity in air, it is possible to infer that the slow sound phenomenon is more pronounced at the bottom of THE composite meta-absorber, due to the different combinations of lateral plates and cavities. The coupling relationship between internal loss and radiation loss of the meta-absorber was revealed using the zero and pole method, proving the ultra-broadband and quasi-perfect sound absorption characteristics. Tests of the sound absorption coefficient in impedance tubes and reverberation chambers confirm the effective broadband sound absorption performance. The composite meta-absorber in this study can be directly used to reduce broadband noise. Moreover, it also provides ideas for the design of sound-absorbing metamaterials.

Response of the mid-latitude ionosphere to the solar eclipse on 25 October 2022: Results of F2–layer vertical sounding

The results of observations of the critical frequency (foF2), ionospheric F2 peak electron density (NmF2) and peak height (hmF2) of the ionosphere over Kharkiv (Ukraine, 49.6° N, 36.3° E) during a partial solar eclipse (SE) on 25 October 2022 are presented. The data analysis showed a clear effect in the variations of foF2 (and, accordingly, NmF2): during the SE, foF2 decreased, and 5 min after the time of maximum eclipse, began to increase to its usual level. From the beginning of the SE, hmF2 decreased from 285 to 255 km, and then it began to grow with a maximum near the time of maximum obscuration. To study longitudinal effects and clarify contributions of different factors to the observed temporal variations of the ionospheric parameters, the results of observations of the ionosphere over Kharkiv were compared with the data obtained by the ionosonde in Pruhonice (Czech Republic, 50.0° N, 14.6° E). The NmF2 electron density decreased due to SE by the factor of 1.46 in Kharkiv, in contrast to 1.33 times in Pruhonice. Comparison of data in universal time (UT) showed a coincidence in the nature and time of fluctuations in both foF2 and hmF2 observed in Kharkiv and Pruhonice on 25 October. Variations in hmF2 caused by SE in Kharkiv and Pruhonice were identical. The SE was accompanied by a plasma flow from the plasmasphere to the ionosphere. The flux density change was about –2 × 1013 m–2s−1 and about 0 for Kharkiv and Pruhonice, respectively. The obtained value of the vertical velocity (tens of meters per second) for Kharkiv is the typical velocity for the mid-latitude F2 layer of the ionosphere. It was confirmed that in addition to typical SE effects, results of observations of the ionosphere over Kharkiv on October 25, 2022 had individual features.

Localized Blowing for Near-Wake Flow and Vortical Structure Control in Turbulent Boundary Layers Over Periodic Two-Dimensional Roughness

Abstract Volumetric three-component flow measurements were made to investigate localized blowing (injection) as a control strategy for turbulent boundary layers over k-type two-dimensional (2D) roughness. The flow measurements were made using particle tracking velocimetry at a Reynolds number of 100,000, based on the freestream velocity and boundary layer thickness. The roughness occupied ∼13% of the boundary layer thickness and consisted of transverse square bars positioned periodically at a pitch-to-height ratio of 11. Two cases were considered: a baseline case without blowing and a case with blowing through five spanwise jets issuing from the downstream face of the 11th bar. The results highlight the effectiveness of blowing in reducing the size of the recirculation zone and turbulence past the bar. Specifically, the spanwise-averaged flow field for the blowing case shows a 40% reduction in the reattachment length and ∼25% reduction in the maximum Reynolds shear stress relative to the baseline case. Moreover, visualizations of the vortical structures past the bars for the baseline case display coherent spanwise vortices similar to those observed past isolated 2D bars and backward-facing steps; however, the spanwise vortices observed here exhibit more three-dimensionality likely due to the turbulence enhanced by upstream bars. Blowing disrupts these spanwise vortices and produces new vortical structures with a wall-normal sense of rotation, although significantly weaker than the spanwise vortices. As such, blowing results in a reduction in the spanwise-averaged spanwise vorticity characteristic of the flow over k-type 2D roughness. The disruption of the spanwise vortices and the reduction in the size of the recirculation zone are likely responsible for the reduction in the Reynolds shear stress and turbulent kinetic energy in the near wake.