The wake of two surface-mounted cubes in tandem features complex flow regimes, which include intermittent reattachment at small spacing ratios L / D , changing to a cavity-locked regime and synchronized shedding at higher L / D . While the mean flow field has been widely studied, the dynamic processes responsible for these regimes require further investigation, motivating the present study. The dynamic flow field around two surface-mounted cubes in tandem with L / D = 2 , 2.5, and 4 was investigated based on large-eddy simulations of the flow for R e = 1 & times; 10 (4) and a turbulent ground plane boundary layer of thickness delta / D = 0.8 . A finite-impulse response filter-based spectral proper orthogonal decomposition was performed on the three-dimensional flow field, revealing an unsynchronized shedding regime with two co-existing modes for L / D = 2 . Mode A was characterized by vortex shedding from the downstream cube at a higher frequency, while mode B featured stronger but low-frequency shear layer oscillation from the upstream cube. A transition state was observed for L / D = 2.5 and a fully synchronized shedding regime was observed for L / D = 4 . A low-frequency drift mode was identified for all cases, with two modes for L / D = 4 . The drift mode was found to trigger mode A for L / D = 2 , and it showed a correlation with the reverse flow region, downwash intensity, and fluctuating drag force on the cubes for all L / D . While the downstream cube wake did not change significantly with L / D , an alternate shedding of base-like vortices was found, distinguishing it from the wake of an isolated cube.

The mean flow field around two surface-mounted cubes in tandem was investigated through large-eddy simulations at a Reynolds number of Re = 1 x 104 and with a turbulent boundary layer of thickness SID = 0.8 at the location of the upstream cube. Center-to-center spacing ratios of LID = 2, 2.5 and 4 were considered to describe the intermittent reattachment, cavity-locked and synchronized shedding regimes, respectively. The mean flow features were related to the near-surface flow field of the cubes and their drag and normal force coefficients. Although an arch vortex was always present behind the upstream cube, the flow in the gap changed significantly depending on the different flow regimes, affecting the shape, size and strength of the arch vortex. The flow field surrounding the upstream cube did not change significantly with LID, presenting a similar near-surface flow field to an isolated cube. The near-surface flow for the downstream cube changed from a reattachment pattern for LID = 2, to impingement for LID = 2.5, to flow separation from the leading edges and the appearance of a second horseshoe vortex for LID = 4. The arch vortex of the downstream cube was uniquely shaped and similar for all LID, due to flow separation from the cube's rear edges. Base-like streamwise vorticity regions were present in the downstream cube's wake, which suggest they may be the time-averaged signature of the vortices shed from the cube.

Low-head dams and weirs often form submerged hydraulic jumps downstream, resulting in numerous fatalities due to the entrapment of persons within the jumps. Developing mitigative measures is a key priority for improving public safety at these structures. An array of parallel angled vanes placed on the channel bed has been tested as a potential retrofit. The vanes eliminated the submerged hydraulic jump and redirected the flow to carry a person toward the channel bank or downstream. This study was carried out to assess how a human body might interact with the vanes as it is moved by the flow. Thc cxperimcnts uscd 3D-printed scale models of Canadian adult male bodies, designed to replicate the human body mass distribution and joint mobility. Three test bodies of identical dimensions but varying densities, with specific gravities of 0.976, 1.018, and 1.052, were developed. Tests involved an array of three rectangular plates angled at 20 to the flow and placed on the downstream channel bed below a sharp-crested weir. The tests were conducted under varying flow rates and tailwater depths. For each flow condition and two insertion locations of the test body into the flow, ten trials were conducted to examine the repeatability of observing a particular body-vane interaction. Observations showed that the results were not repeatable, likely due to the variability in limb movement within the turbulent flow. Similarly, body density strongly influenced interactions, with denser bodies engaging with the vanes less frequently and exhibiting different interaction patterns.

The flow around a surface-mounted cube has been investigated for decades, yet the fundamentals of the mean flow have not been updated to reflect the latest advances regarding the flow around surface-mounted finite-height square prisms in general. One of the main gaps is the flow field very near the cube walls, especially the sides, and its relationship to the near wake. To investigate these features, large-eddy simulations of the flow around a surface-mounted cube were carried out at a Reynolds number Re =1×104. Two boundary layers were considered: a thin and laminar boundary layer and a thick and turbulent one, to provide an overview of the flow around the cube for contrasting boundary layers. The major flow structures in the mean wake were the horseshoe vortex, the arch vortex and the dipole structures, with other regions of vorticity also present. The time-averaged flow fields presented similar flow features for both boundary layers, but the thicker and turbulent one caused the horseshoe vortex to be located closer to the cube, the wake to become narrower and shorter, the coherent structures and downwash to weaken, the pressure to decrease around the sides and top of the cube, the drag force coefficient to decrease, the normal force coefficient to increase, and the trailing edge vortices to weaken. Intermittent flow reattachment on the top and side faces of the cube, as well as corner vortices, were found for both boundary layers, while the side and free end vortices were found exclusively with the thicker boundary layer, yielding a headband vortex. The three-dimensional flow structures and features were related to the near-wall flow field on the cube and ground plane surfaces, giving a complete and updated description of the mean flow characteristics.

Interference effects on the mean flow field, aerodynamic forces, and vortex shedding in the wakes of two cubes in tandem have been experimentally investigated, considering different boundary layer thicknesses of delta/D=0.8 and 1.3. The cubes had center-to-center longitudinal spacing ratios of L/D=1.5 to 5 and were exposed to an incoming flow with a Reynolds number of Re =7.5x10(4)- 9x10(4) based on the cubes' width D and the freestream velocity. For the thin boundary layer, the flow showed an intermittent regime with two Strouhal numbers for L/D<2.25, a co-shedding regime with synchronized shedding for L/D>2.25, and evidence of a cavity-locked regime around L/D=2.75. The intermittent regime featured flow reattachment but was not bistable, corresponding instead to unsynchronized shedding from both the upstream and downstream cubes. The mean drag force, normal force, and bending moment coefficients were examined across the regimes as functions of L/D and delta/D, showing greater variation for the downstream cube. Particle image velocimetry measurements revealed that the probability of reattachment on the downstream cube decreased, a second horseshoe vortex formed in the gap, and flow separated from the downstream cube's leading edges for high L/D. When increasing delta/D, vortex shedding from the upstream cube was delayed, leading to a high Strouhal number single-wake regime for L/D<2.5. The shorter formation region caused fluid to enter the gap, giving higher drag force coefficients for the downstream cube for small L/D, while the decreased probability of reattachment on the top of the cube led to a small increase in its normal force coefficient.

Motivated by contradicting or insufficient information regarding the large-scale flow dynamics around surface-mounted finite-height square prisms of small aspect ratio, the present study investigates the dominant vortex shedding and low-frequency dynamics around a surface-mounted cube. These flow modes were obtained from the spectral proper orthogonal decomposition of large-eddy simulation results, at a Reynolds number of $\textit {Re}=1\times 10^4$ and two different types of boundary layer: a thin and laminar boundary layer with thickness $\delta /D=0.2$ and a thick and turbulent boundary layer with $\delta /D=0.8$ . The main antisymmetric mode pair revealed a new flow pattern with the alternate shedding of streamwise flow structures, indicating a transition from the half-loops of taller prisms to only streamwise strands (i.e. no vertical core) for smaller aspect ratio. The formation process of the streamwise structures is due to a reorientation of the vorticity of the arch vortex in the streamwise direction characteristic of the shed structures. The low-frequency drift mode affected the length of the recirculation region, the strength of vortex shedding, and the near-wall flow field and pressure distribution on the cube's faces, leading to low-frequency variations in the fluctuating drag and normal force coefficients. These large-scale flow dynamics were similar for both boundary layers, but minor differences were identified, related mostly to the occurrence of flow attachment and the formation of a headband vortex for the thicker boundary layer.

One tradeoff in design of protective clothing for firefighters and other workers is between thermal protection and thermal stress management. Standard methods for assessing thermal stress management of protective clothing include guarded hot plate and mannequin tests. In this study, a fabric-covered heated cylinder was used in a wind tunnel to measure convection heat transfer coefficients and thermal resistance at various air speeds. Measurements demonstrated the impact of air permeability and wind speed on these parameters. When the cylinder was covered with low permeability fabrics, convection heat transfer coefficients were similar to values predicted using a correlation for bare cylinders. Thermal resistance measurements generally ranked fabrics in the same order as guarded hot plate tests. This cylinder test is more representative of the body's geometry than hot plate tests, but less expensive to conduct than mannequin tests, and could serve as a bridge between these two tests for design purposes.

The flow downstream of surface-mounted finite height square prisms with aspect ratio AR = 1 (cube) and 0.5 (block) was investigated experimentally in a low-speed wind tunnel, to determine the overall structure and dynamic behavior of the wake and the source of the streamwise vorticity. The Reynolds number based on the prisms' width D was Re = 7:5 x 10(4) and the boundary layer thickness at the location of the prisms was delta/D = 0:73. A vortex shedding frequency was found in the wake of the cube, but no periodicity was found in the wake of the block. The mean wake of the cube showed features of prisms below the critical AR, but the wake of the block had a distinct behavior due to the dominant shear flow from the boundary layer. The shear changed the downwash and, consequently, the streamwise vorticity distribution in the wake, in addition to reducing the magnitude of the Reynolds stresses. The phase-average analysis for the cube revealed the alternate shedding of inclined structures related to the streamwise vorticity in the upper part of the wake. These vorticity regions were caused by the alternate bending and entrainment of the side flow, caused by the downwash. The periodic component of the total Reynolds stresses was, however, significantly smaller than the turbulence-related stresses. This study showed that the wake had a transitional behavior for the cube, but became fundamentally different for the block when compared with prisms of higher AR.

The mean flow field, aerodynamic forces, bending moment and Strouhal number (St) were investigated for isolated surface-mounted finite-height square prisms of very small aspect ratio (AR). The Reynolds number was Re =7.5×104 for the velocity measurements and 9×104 for the force, bending moment and St measurements. Prisms with AR = 0.5, 0.7 and 1 were considered, under two different boundary layer thicknesses of δ/D=0.7–0.8 (thin) and δ/D=1.3 (thick). For both boundary layers, the mean drag force coefficient showed a sharper increase with AR compared with taller prisms, and the mean normal force coefficient increased smoothly, with a lower magnitude than pressure-based normal force coefficients. An approximately constant point of action of the drag force was found for AR < 1. While the thick boundary layer caused the spectral peaks to weaken and St to decrease, some periodicity was still found for all AR. These features were connected to the changes in the mean wake of the prisms with AR and δ/D. A smaller AR and larger δ/D had similar effects, causing the wake to shorten, the probability and type of reattachment of the flow on the free end to change, and the mean wake structure to transition from a streamwise wake vorticity pattern to an inner vorticity pattern. The prism with AR = 1 showed a dipole wake structure similar to that of taller prisms, while the unique wake topology of prisms with AR < 1 was found to be responsible for the different force and St trends identified in this range of AR.

HighlightsAir velocity data were measured at seven lateral positions across the width of a modern high-clearance sprayer at multiple vertical and downstream locations relative to the nozzles. Velocity components were measured in three directions.Complex flow patterns were present behind the sprayer tractor and rear tires. An upward velocity component was measured below and downstream of the nozzles at many of the sensor locations.Elevated turbulent kinetic energy was measured downstream of the structural elements required for reconfiguring the boom structure into the transport position.Abstract. With growing pressure for increased efficiency and productivity on large farms throughout North America, high-clearance sprayers have become large machines that are operated at relatively high speed when applying pesticides during the growing season. Minimizing pesticide drift remains paramount to the safe and responsible operation of these machines. With the aim of both improving the understanding of high-clearance sprayer wake features, and to aid in the validation of numerical models of a full-scale sprayer using computational fluid dynamics (CFD), time-averaged velocity components and turbulent kinetic energy (TKE) in the wake of a sprayer were measured and reported during simulated field operation. Data were collected at various locations in the wake of a sprayer at two operating speeds (4 and 11 m s-1) at two boom heights. Ultrasonic anemometers were located directly behind the sprayer, immediately beside the sprayer tractor, and farther down the boom away from the influence of the tractor. Complex flow patterns were present behind the sprayer tractor and rear tires. An upward velocity component was measured below and downstream of the nozzles at many of the sensor locations. The magnitude of turbulence, upward velocity, and velocity deficit generally increased as the reference airspeed (travel speed combined with headwind contributions) increased. A lower boom height reduced the severity of these detrimental wake characteristics near the sprayer tractor; in general, a lower boom is known to reduce the potential of spray drift. Overall, this experimental study illustrates the variation in wake features behind a modern high-clearance sprayer under different operating conditions. Keywords: High-clearance sprayer, Spray drift, Turbulent wake, Ultrasonic anemometer.

The mean wake of a three-dimensional surface-mounted rectangular flat plate was studied experimentally in a low-speed wind tunnel for four different aspect (height-to-width) ratios, AR = 3, 2, 1, and 0.5. The Reynolds number based on the plate width was Re = 3.8 × 10 4 and the boundary layer thickness on the ground plane, relative to the plate width, was δ / W = 1.1. The incidence angle of the plate was varied from α = 0° (where the plate is normal to the flow) to α = 90° (where the plate is parallel to the flow). The mean velocity and vorticity fields in the wake were measured using a seven-hole pressure probe. At α = 0°, the length of the recirculation zone behind the plate becomes progressively shorter as the aspect ratio is lowered and follows the same tendency as that of a finite square prism. The wakes of the slenderer flat plates of AR = 3 and 2 are characterised by two pairs of streamwise vortices: a pair of tip vortices in the upper wake and a pair of ground-plane vortices on the lower edges of the wake. With increasing incidence angle, a single tip vortex comes to dominate the wake, secondary vorticity is induced at various locations, a ‘traffic light’ vortex pattern may form, and ultimately a familiar wing-tip (trailing) vortex develops. In contrast, flow downstream of the less slender flat plates of AR = 1 and 0.5 is characterised by a single pair of large streamwise vortices, which become asymmetric with increasing incidence. Close to the flat plate of AR = 0.5, and at small incidence angles only, a unique pair of small inner vorticity concentrations, of opposite sense of rotation to the main streamwise vortices, is found in the upper part of the wake.

In this experimental study, the mean pressure distribution was measured on the free end of a surface-mounted finite-height square prism for different aspect ratios, incidence angles, and boundary layer thicknesses. The Reynolds number based on the width of the prism was kept constant at Re = 6.5 x 10(4), the aspect ratio of the prism was changed from AR = 1 to 11, and the incidence angle was varied in small increments from alpha = 0 degrees to 45 degrees. The thickness of the boundary layer on the ground plane relative to the prism width was either delta/D = 0.8 or delta/D = 2.6, representing a thin or thick boundary layer. When the prism was oriented at alpha = 0 degrees, distinct mean pressure distributions were observed for prisms nearly or completely immersed in the boundary layer, and also for the very slender high-aspect ratio prisms. The mean normal force coefficient steadily increased with the aspect ratio but its value decreased in the presence of the thicker boundary layer. When the prism was oriented at alpha = 45 degrees, strong pressure gradients were encountered near the leading edges for prisms nearly or completely immersed in the boundary layer, and the conical vortex angles increased with aspect ratio. For intermediate aspect ratios, these pressure gradients weakened and the vortex angles became insensitive to AR. When the incidence angle was between 0 degrees and 45 degrees, the asymmetric mean pressure distribution meant that the conical vortices were located at different angles. The position of the conical vortex located more centrally above the free end was more sensitive to changes in aspect ratio. The influence of the boundary layer on the vortex angles was more pronounced for smaller aspect ratios. In addition, the behaviour of the normal force coefficient with incidence became more complex for higher aspect ratios.

Different flow models have been proposed for the flow around surface-mounted finite-height square prisms, but there is still a lack of consensus about the origin and connection of the streamwise tip vortices with the other elements of the wake. This numerical study was performed to address this gap, in addition to clarifying the relationship of the near-wake structures with the far wake and the near-wall flow, which is associated with the fluid forces. A large-eddy simulation approach was adopted to solve the flow around a surface-mounted finite-height square prism with an aspect ratio of AR = 3 and a Reynolds number Re = 500. The mean drag and normal forces and the bending moment for the prism were quantitatively compared in terms of skin-friction and pressure contributions, and related to the near-wall flow. Both three-dimensional visualizations and planar projections of the time-averaged flow field were used to identify, qualitatively, the main structures of the wake, including the horseshoe vortex, corner vortices and regions of high streamwise vorticity in the upper part of the wake. These features showed the same qualitative behavior as reported in high Reynolds number studies. It was found that some regions of high streamwise vorticity magnitude, like the tip vortices, are associated with the three-dimensional bending of the flow, and the tip vortices did not continuously extend to the free end of the prism. The three-dimensional flow analysis, which integrated different observations of the flow field around surface-mounted finite-height square prisms, also revealed that the mean near-wake structure is composed of two sections of different origin and location of dominance.

A systematic set of low-speed wind tunnel experiments was performed at Re = 6.5 x 10(4) and 1.1 x 10(5) to study the mean wind loading experienced by surface-mounted finite-height square prisms for different aspect ratios, incidence angles, and boundary layer thicknesses. The aspect ratio of the prism was varied from AR = 1 to 11 in small increments and the incidence angle was changed from alpha = 0 degrees to 45 degrees in increments of 1 degrees. Two different boundary layer thicknesses were used: a thin boundary layer with 6ID = 0.8 and a thick boundary layer with delta/D = 2.0-2.2. The mean drag and lift coefficients were strong functions of AR, alpha, and delta/D, while the Strouhal number was mostly influenced by alpha. The critical incidence angle, at which the prism experiences minimum drag, maximum lift, and highest vortex shedding frequency, increased with AR, converged to a value of alpha(c) = 18 degrees +/- 2 degrees once AR was sufficiently high, and was relatively insensitive to changes in delta/D. A local maximum value of mean drag coefficient was identified for higher-AR prisms at low alpha. The overall behaviour of the force coefficients and Strouhal number with AR suggests the possibility of three flow regimes.

Wind tunnel experiments at a Reynolds number of Re = 6.5 x 10(4) were used to study the effect of aspect ratio and boundary layer thickness on the mean static pressure distribution on the free end of a surface-mounted finite-height cylinder. The cylinder's aspect ratio was changed in small increments from AR = 0.5 to AR = 11. Two different boundary layer thicknesses (relative to the cylinder diameter) were employed, delta/D = 0.6 and delta/D = 1.9. From analysis of the mean pressure contour plots, it was found that the sizes and locations of regions of lower pressure, adverse pressure gradient, and higher pressure, and the appearance of "eye-like spots", are sensitive to both AR and delta/D. The adverse pressure gradient occurs just ahead of the mean reattachment line while the eye-like spots are related to termination points of the legs of the arch vortex within the free-end mean recirculation zone. The total normal force coefficient experienced by the cylinder is strongly influenced by the contribution of the wall shear stress on the sides of the cylinder, with a change in direction of the net vertical shear stress contribution occurring between AR = 7 and AR = 8 for both boundary layers.

A brief review of the literature for the flow around two surface-mounted finite-height cylinders in a staggered configuration illustrates some of the additional complexity associated with changes in the cylinder aspect ratio (AR), the effects of downwash, the three-dimensional structure of the wake, and the presence of additional vortex structures. To date, however, few extensive systematic studies of centre-to-centre pitch ratio (P/D), incidence angle ( α), aspect ratio, boundary layer thickness on the ground plane (δ/D) and Reynolds number (Re) have been reported for two finite cylinders. Some new measurements of the mean drag and lift coefficients (CD and CL) and the Strouhal numbers (St) for two staggered finite cylinders, for AR = 9, 7, 5, and 3, P/D=1.125–4.5, and α = 0∘–90°, at Re = 6.5×104 and δ∕D=1.4, illustrate the moderating effect of the three-dimensional flow on the wind loading and vortex shedding behaviour compared to the flow around two infinite cylinders. These new results suggest some changes to the flow pattern boundaries and uncover some new trends in the CD, CL and St data with P/D and/or α; there is a need for new flow visualization, flow field measurements, and numerical simulations to advance physical interpretation.

Wind tunnel experiments were performed at Re = 6.5 x 10(4) to measure the mean drag and normal forces, mean bending moment, and vortex shedding frequency for surface-mounted finite-height cylinders. The cylinder aspect ratio was varied in small increments between AR = 0.5 and 11, and two different boundary layer thicknesses were used, delta/D = 0.6 and 1.9. Small increments in AR and use of a single Re helped clarify some AR effects for finite cylinders. The data allowed a more precise definition of the familiar critical aspect ratio to be set, based on the behaviour of the mean aerodynamic forces and the point of action of the mean drag force. A second change in behaviour of the aerodynamic forces with AR was also identified; this transition was related to changes in the vortex formation length, the development of the near-wake recirculation zone, and the influence of the two main near-wake vortex structures, with AR. The general effects of increasing delta/D are to lower the force and moment coefficients and Strouhal number, increase the critical AR, and increase the AR where the second transition occurs.

OBJECTIVE To compare laryngeal impedance, in terms of air flow and pressure, following arytenoid corniculectomy (COR) versus 3 other airway interventions (left-sided laryngoplasty with ipsilateral ventriculocordectomy [LLP], LLP combined with COR [LLPCOR], and partial arytenoidectomy [PA]) performed on cadaveric equine larynges with simulated left recurrent laryngeal neuropathy (RLN) and to determine whether relative laryngeal collapse correlated with the interventions performed. SAMPLE 28 cadaveric equine larynges. PROCEDURES Each larynx in states of simulated left RLN alone and with airway interventions in the order LLP, LLPCOR, COR, and PA was evaluated in a box model construct that replicated upper airway flow mechanics consistent with peak exercise in horses. Results for impedance, calculated from airflow and pressure changes, were compared between states for each larynx. Multivariable mixed-effects analysis controlling for repeated measures within larynx was performed to calculate the predicted mean impedance for each state. RESULTS Results indicated that tracheal adapter diameter, individual larynx properties, airway intervention, and relative laryngeal collapse affected laryngeal impedance. The LLP and LLPCOR interventions had the lowest impedance, whereas the COR and PA interventions did not differ substantially from the simulated left RLN state. Residual intraclass correlation of the model was 27.6%. CONCLUSIONS AND CLINICAL RELEVANCE Although impedance was higher for the simulated left RLN with the COR intervention state than with the LLP intervention state, given the clinical success of PA for treating RLN in horses and the similar results for the COR and PA intervention states in the present study, the use of COR warrants further investigation. The residual interclass correlation suggested that individual laryngeal variation affected impedance and may have a clinical effect.

A finite-height square prism immersed in a low Reynolds number uniform flow is visualized based on the mean velocity field generated by a large eddy simulation. The flow about the free-end of the prism, which connects directly into the wake, is analyzed in terms of the three-dimensional flow structure. A strong reverse flow exists along the surface of the free-end, which is supplied by the upward flow generated along the rear face of the prism by the primary vortex/recirculation zone in the wake. Two streamwise vortical structures are generated at the lateral corners of the leading edge of the prism. The structures grow in strength and their location moves toward the mid-plane of the prism flow field as they extend downstream. Cross-stream sections show that the reverse flow on the free-end also entrains fluid from the lateral sidewalls.