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Swimmers primarily increase their forward velocity through lower limb motion in breaststroke, making the breaststroke kick crucial for optimizing race times. Recent studies have highlighted the generation of vortices around the swimmer’s entire body to propel forward during swimming. However, the investigation of vortex generation during breaststroke kicks remains unexplored. This study aimed to reveal the propulsive and braking mechanisms of breaststroke kicks by simulating vortex generation using computational fluid dynamics (CFD). Kinematic data during the breaststroke kick and a three-dimensional digital model were collected to conduct CFD for a male breaststroke swimmer. Vortex generation was determined during one breaststroke kick from the CFD results. Vortices, which potentially induce a decrease in forward velocity, were generated by the swimmer’s lower legs and feet during the recovery phase. The swimmer generated vortices on the dorsal side of the feet and the posterior and lateral sides of the lower legs to increase the forward velocity during the out-sweep phase. The swimmer generated vortices on the lateral sides of the thighs and lower legs and the dorsal and lateral sides of the feet during the in-sweep phase to maintain forward velocity. Moreover, vortices generated from the out-sweep to the in-sweep merged and were shed backward relative to the swimming direction after the in-sweep phase. This study is the first to reveal the propulsive and braking mechanisms of breaststroke kicks by analyzing the vortex generation.

Micro free-flow electrophoresis (μFFE) provides a rapid and straightforward route for the high-performance online separation and purification of targeted liquid samples in a mild manner. However, the facile fabrication of a μFFE device with high throughput and high stability remains a challenge due to the technical barriers of electrode integration and structural design for the removal of bubbles for conventional methods. To address this, the design and fabrication of a high-throughput μFFE chip are proposed using laser-assisted chemical etching of glass followed by electrode integration and subsequent low-temperature bonding. The careful design of the height ratio of the separation chamber and electrode channels combined with a high flow rate of buffer solution allows the efficient removal of electrolysis-generated bubbles along the deep electrode channels during continuous-flow separation. The introduction of microchannel arrays further enhances the stability of on-chip high-throughput separation. As a proof-of-concept, high-performance purification of fluorescein sodium solution with a separation purity of ~97.9% at a voltage of 250 V from the mixture sample solution of fluorescein sodium and rhodamine 6G solution is demonstrated.

The aerodynamic characteristics are concerned with the fuel consumption rate and the stability of a high speed vehicle. The current research aims at studying the aerodynamic behavior of a typical SUV vehicle model mounted with the vortex generator (VG) at various linear positions with reference to its rear roof edge. The flow field around the vehicle model was observed at different wind speed conditions. It had been determined that at the instance of lower wind speed, the VG had minimal effects of aerodynamic drag on the vehicle body. However, at the instance of higher wind speed conditions the magnitude of the drag force decreased significantly. Vehicles move at higher speeds in the highways, location of the VG varied towards the upstream of the vehicle due to early flow separation. Therefore test were conducted at different wind speeds and locations of VG. The numerical simulation conduced in this study provides flow characteristics around the vehicle model for different wind speeds. The realizable k−ε model was used to simulate and validate the empirical results in an effective manner. By using experimental data, the drag was reduced by 9.04 % at the optimized VG location. The results revealed that the induced aerodynamic drag would determine the best car shape. This paper provides a better understanding of VG positioning for enhanced flow separation control.

Flow separation at the upstream side of lateral turnouts (intakes) is a critical issue causing eddy currents at the turnout entrance. It reduces the effective width of flow, turnout capacity and efficiency. Therefore, it is essential to identify the dimensions of the separation zone and propose remedies to reduce its dimensions. Installation of 7 types of roughening elements at the turnout entrance and 3 different bed invert levels, with 4 different discharges (making a total of 84 experiments) were examined in this study as a method to reduce the dimensions of the separation zone. Additionally, a 3-D Computational Fluid Dynamic (CFD) model was utilized to evaluate the flow pattern and dimensions of the separation zone. Results showed that enhancing the roughness coefficient can reduce the separation zone dimensions up to 38% while the drop implementation effect can scale down this area differently based on the roughness coefficient used. Combining both methods can reduce the separation zone dimensions up to 63%.

Chemical base flow separation is a widely applied technique in which contributions of groundwater and surface runoff to streamflow are estimated based on the chemical composition of stream water and the two end‐members. This method relies on the assumption that the groundwater end‐member can be accurately defined and remains constant. We simulate solute transport within the aquifer during and after single and multiple river flow events, to show that (1) water adjacent to the river will have a concentration intermediate between that of the river and that of regional groundwater and (2) the concentration of groundwater discharge will approach that of regional groundwater after a flow event but may take many months or years before it reaches it. In applying chemical base flow separation, if the concentration in the river prior to a flow event is used to represent the pre‐event or groundwater end‐member, then the groundwater contribution to streamflow will be overestimated. Alternatively, if the concentration of regional groundwater a sufficient distance from the river is used, then the pre‐event contribution to streamflow will be underestimated. Changes in concentration of groundwater discharge following changes in river stage predicted by a simple model of stream‐aquifer flows show remarkable similarity to changes in river chemistry measured over a 9 month period in the Cockburn River, southeast Australia. If the regional groundwater value was used as the groundwater end‐member, chemical base flow separation techniques would attribute 8% of streamflow to groundwater, as opposed to 25% if the maximum stream flow value was used.

This investigation is aimed to look at the significance of Joule heating and aligned magnetic effects in porous media saturated by a Ti-alloy/multi-wall carbon nanotube (MWCNT)-water based hybrid nanofluid in the presence of heat generation and velocity slip toward an exponentially shrinking surface. The Tiwari–Das approach is used to develop the mathematical modeling, which is then converted into system of nonlinear ODEs using appropriate similarity transformations. The dual solutions are noticed for the resultant boundary value problem using Newton–Raphson and Runge–Kutta based shooting scheme and then the comparative analysis is provided with existing results. Among these solutions, the first solution is found to be more stable and physically valid over time according to the smallest eigenvalue approach of linear temporal stability analysis. The important outcomes of this study, based on the stable solutions, are: (i) the hybrid nanofluid’s Nusselt number, skin friction, velocity and temperatures rise when the inclined magnetic parameter rises, (ii) the delay of boundary layer separation is noticed with enhancing values of the first-order slip, Darcy porosity and inclined magnetic parameters, (iii) the value of smallest eigenvalue is growing with growing values of the inclined magnetic parameter, and (iv) the thickness of momentum and thermal boundary layers is thinner for the first solution than the second solution. In addition, the delay in boundary layer separation occurs with increasing values of the first-order slip, porosity, and aligned magnetic parameters and decreasing values of the Joule heating parameter. Finally, the streamline patterns are provided in this study to have a better understanding of the fluid flow behavior.

Dual Bell nozzles are increasingly investigated as an altitude-compensating technology in rocket propulsion, offering higher efficiency across varying ambient pressures compared to conventional bell nozzles. Their geometry includes an inflection point along the nozzle wall, designed to induce controlled flow separation at low altitudes and flow reattachment at higher altitudes. However, unstable or premature separation can cause performance losses and side loads. To mitigate these issues, active flow control techniques have been introduced, with secondary injection proving to be particularly effective in manipulating flow behavior, delaying separation, and enhancing overall nozzle performance. In this research, a computational fluid dynamics (CFD) investigation is carried out to analyze the effect of secondary injection directions and locations on flow separation and stability within a Dual Bell nozzle. Four injection orientations (tangential, horizontal, inclined, and normal) are systematically studied at three nozzle sites: the inflection point, the middle of the base nozzle, and the middle of the extension nozzle. Numerical simulations are performed using ANSYS FLUENT, applying the Navier–Stokes transport equations, continuity, and energy equations in conjunction with the k-ω SST turbulence model to capture shear stress transfer. Due to nozzle symmetry, only half of the geometry is modelled. The analysis focuses on the resulting flow field, including shockwaves, boundary layer interactions, separation points, and reattachment zones. The results demonstrate that both injection direction and placement strongly influence flow separation characteristics. Tangential injection at the inflection point is identified as the most effective configuration, generating streamwise vortices that control shock-boundary layer interactions, delay separation onset, and stabilize the transition between operating modes with minimal pressure loss. NPR effect on the flow behavior is studied for the optimum case. Overall, the investigation confirms that secondary injection is a promising active flow control method for optimizing stability and efficiency in Dual Bell nozzles.

Vortex shedding due to flow over a main cylinder (MC) has been investigated numerically using a rotating control cylinder (CC) for the effective control of shedding characteristics and possible suppression. The state of the art concerning the investigation is “the location of control cylinder” which is kept in the “flow separation region of MC”. The study is conducted in an unconfined, unsteady flow region, in which the flow is assumed to be two-dimensional at the Reynolds number (Re) 100. The rotational speed of CC ( α  = 0 to 2) and the radial distance between the centres of MC and CC ( R d / D  = 0.6 to 1) are taken as the study parameters, where D is the diameter of the main cylinder. The instantaneous flow field variables are computed using the finite volume-based CFD solver Ansys Fluent (15.0). The vortex shedding characteristics are presented in the form of streamlines, Strouhal number (St), drag coefficient ( C D ) and lift coefficient ( C L ). It is interesting to note that the CC located away from the MC ( R d / D  = 1) suppresses the shedding, whereas control cylinder located very close to the MC has less significant in shedding control, which depends mainly on the flow approaching the gap between MC and CC. At R d / D  = 1, the shedding is suppressed with reduced drag around 20% as compared to MC cylinder without CC; the reduction percentage increases with the increasing rotational speed of CC ( α ).

Rapid development of the anomalous enhancement of separated turbulent Re = 6000 air flow and heat transfer in an in-line single-row package of 31 inclined grooves, 0.2 in dimensionless depth, in a singled-out longitudinal region of the wall of a narrow channel is studied. It is due to the interference of vortex wakes behind the grooves and the acceleration in the channel flow core with the formation of a zone of ultrahigh longitudinal velocity. The wave-shaped parameter characteristics are stabilized in the region of approximately 15th groove, whereupon the oscillation amplitudes are moderately reduced. The return flows in the grooves are enhanced with distance from the entry section, the minimum negative friction diminishing from −2 to −4. The total relative heat removal from the structured region increases at q = const by a factor of approximately 2.75 and by the factor of two at T  = const with increase in the relative hydraulic losses by the factor of 1.7, as compared with the case of a plane–parallel channel. The relative heat removal from the surface bounded by the contour of the 20th inclined groove amounts to 3.7 ( q = const) with increase in the hydraulic losses by the factor of 2.2. An increase in the local maximum of the longitudinal velocity up to a factor of 1.5, as compared with the mean-mass velocity, can be observable.

The current study investigates the effect of passive flow control strategy to enhance the aerodynamic performance of vertical axis wind turbines (VAWTs), by positioning a passive flow separator (PFS) adjacent to the blade’s leading edge. Using a 2D computational fluid dynamics (CFD) analysis with the shear stress transport (SST) turbulence model to solve the unsteady Reynolds average Navier stokes (URANS) equations, the S1046 aerofoil is investigated under incompressible flow conditions. A range of PFS diameters is tested, with diameter-to-chord ratios (d/c) of 0.0428, 0.05, and 0.054. Results show that incorporating a PFS delays flow separation and significantly improves turbine performance compared to the baseline turbine. The highest power coefficient ( Cₚ ) is achieved at d/c = 0.05, with an enhancement of approximately 27.9%. Additional simulations using different aerofoils reveal that the NACA0012 profile, combined with a circular PFS, yields the highest Cₚ showing a performance gain of up to 45% over others PFS shapes. The impact of turbine solidity is also analyzed, with optimal improvements observed at a solidity of 0.2.