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This paper numerically investigates the distributed blowing control of the flow around a square cylinder at a low Reynolds number of R e = 200. The air holes are placed at the windward or leeward stagnation points. The control effect of the unsteady aerodynamic forces is notably different with different spanwise distributions of air holes, which is represented by the dimensionless air hole area ratio G. The simulation results indicate that the windward blowing control (WBC) shows better control effect than the leeward blowing control (LBC) in reducing the time-averaged drag coefficient C d ¯ of the square cylinder while the fluctuating lift coefficient C l ′ can be significantly suppressed by the LBC. Besides, the surface pressure distribution, the turbulence kinetic energy (TKE) and Reynolds shear stress (RSS) distributions and the shedding vortices in the wake are analysed and compared in detail under different control conditions. Finally, through the instantaneous 3D vortex structures and the spanwise fluctuating velocity w ′ distribution in the flow field, the suppression of the unsteady aerodynamic forces is mainly related to the 3D vortex pairs induced by the blowing jet. • Distributed blowing was employed to control the flow around a square cylinder. • The spanwise distribution of air holes notably affected the steady blowing flow control. • A 'Six-Vortices Type' vorticity distribution appeared in the flow field under windward blowing control. [ABSTRACT FROM AUTHOR]

We experimentally investigated the flow characteristics around a circular cylinder with a slot at different angles of attack. The experimental campaign was performed in a wind tunnel at the Reynolds number of Re = 2.67 × 10. The cylindrical test model was manufactured with a slot at the slot width S = 0.075 D ( D is the diameter of the cylinder). The angle of attack α was varied from 0° to 90°. In addition to measuring the pressure distributions around the cylinder surface, a digital particle image velocimetry (PIV) system was employed to quantify the wake flow characteristics behind the baseline cylinder (i.e., baseline case of the cylinder without slot) and slotted cylinder at various angles of attack. Measurement results suggested that at low angles of attack, the passive jet flow generated by the slot would work as an effective control scheme to modify the wake flow characteristics and contribute to reducing the drag and suppressing the fluctuating lift. The flip-flop phenomenon was also identified and discussed with the slot at 0° angle of attack. As the angle of attack α became 45°, the effects of the slot were found to be minimal. When the angle of attack α of the slot approached 90°, the self-organized boundary layer suction and blowing were realized. As a result, the flow separations on both sides of the test model were found to be notably delayed, the wake width behind the slotted cylinder was decreased and the vortex formation length was greatly shrunk, in comparison with the baseline case. Instantaneous pressure measurement results revealed that the pressure difference between the two slot ends and the periodically fluctuating pressure distributions would cause the alternative boundary layer suction and blowing at α = 90°. [ABSTRACT FROM AUTHOR]

Background: The application of laminar screws is an alternative fixation for the first thoracic vertebra (T1). This paper is to determine the anatomical characteristics for adequate laminar screw fixation, and present a modified method of sagittal reconstruction of T1 to provide more accurate measurements.Methods: Computed tomography (CT) images of 62 patients (32 males, 30 females) were used for the analysis. The following parameters of the T-1 lamina were measured using Mimics software: lamina length, axis angle, minimal outer cortical width, cancellous width, minimal outer cortical height, cancellous height, and spinous process height. Right or left modified sagittal reconstructions (parallel to right or left screws) were innovatively used for measurement.Results: There were no significant differences between the left and right sides for each measurement performed (P > 0.05), but significant differences were detected between males and females (P < 0.05). The mean length of the T1 lamina was 32.8 mm of the T1 minimal outer cortical width was 7.4 mm, and 3.8% of males had a minimal outer cortical width < 5 mm, while 8.6% of females had a minimal outer cortical width < 5 mm. The mean minimal outer cortical height was 10.8 mm, and 1.9% of males had a minimal outer cortical height < 9 mm, while 7.7% of females had a minimal outer cortical height < 9 mm.Conclusion: This study suggests there are no anatomical limitations for T1 laminar screw placement in most people. The modified sagittal reconstruction method described allows for easy and precise measurement to aid in the insertion of laminar screws in T1, and gives good visualization of laminar screw insertion direction. [ABSTRACT FROM AUTHOR]

Characteristics of flow around a modified circular cylinder are experimentally investigated in the present study. The experimental campaign was performed in a wind tunnel at the Reynolds number of Re = 2.67 × 10 4 , based on the cylinder diameter D and the incoming airflow speed. The cylindrical test model is modified with a slit parallel to the incoming airflow to create a flow communicating channel between the windward and leeward stagnation points. The slit width S changes from 0.05 D to 0.15 D with an increment of 0.025 D. Pressure distributions on the cylinder surface were measured to estimate the aerodynamic forces acting on the test model and a particle image velocimetry (PIV) system was employed to quantify the wake flow patterns of the natural and modified cylindrical test models. Experiment results reveal that a slit contributes to reducing the drag and suppressing the fluctuating amplitude of the dynamic wind loads acting on the test model. The changing trend in drag reduction and lift suppression with the increase of slit width are also discussed based on the surface pressure and PIV measurement results. The PIV measurement results demonstrate clearly that the slit generates a self-issuing jet into the cylinder wake and the passive jet is effective in manipulating the wake vortex shedding process from the circular cylinder. As the jet vortices being shifted downstream, they help to detach the shear layers rolled up from both sides of the circular cylinder. Because of this dynamic interaction process, the antisymmetric pattern of the wake vortex shedding from a natural cylinder is found to be converted to a bistable mode flow behind the slotted cylinders. As a result, the dimensionless vortex shedding frequency is observed to be switched to a very low level and a flip-flop phenomenon is found. A linear stability analysis is then performed to suggest that the intrinsic nature of the cylinder wake flow is greatly modified with the implementation of a slit. [ABSTRACT FROM AUTHOR]

We experimentally investigated the control effectiveness of circular cylinder flow and the mechanism of self-adaptive microfibres inspired by bird feathers. The nylon wires were placed at the front stagnation point of a circular cylinder at a Reynolds number of Re = 2.67 × 10 4 . Surface pressure measurement was employed to analyse the unsteady aerodynamic forces around the circular cylinder, and a high-speed particle image velocimetry measurement system was used to visualise and analyse the wake flow structures. The results indicate that the nylon wires at a high length ratio L/D evidently suppress the Reynolds stress and turbulent kinetic energy, thus suppressing the fluctuating lift and mean drag forces of a circular cylinder. In addition, the nylon-induced vortex at high L/D values can inhibit the interaction of the original shear layers to moderate the von Kármán vortex street behind the cylinder. However, the control effect is limited at low L/D values because the nylon-induced vortex structures cannot reach the wake field and interact with the shear layer. [ABSTRACT FROM AUTHOR]

Triple-box girders, i.e., three separated box girders are arranged in tandem, are gradually used in super-span bridges because of their excellent flutter stability. However, the gaps between triple boxes can lead to complex vortex dynamics around the structures that result in vortex-induced vibrations (VIVs). In the present study, we experimentally investigate VIVs in a long-span bridge with a triple-box girder cross-section using wind tunnel tests. In the static test, in which the test model is fixed, a 'dual-frequency' phenomenon that expands the VIV lock-in region is observed in the global flow field. Furthermore, the results of a dynamic test indicate that the existence of gaps is essential to the occurrence of VIVs in triple-box girders. The smoke-wire flow visualization technique is employed to explore the excitation mechanism by examining the surrounding flow dynamics of the triple-box model. Separated motion-induced vortices (MIVs) and von Karman vortices (KVs) are found to be coupled with structural vibrations to sustain the VIVs. Five stages of VIV regions, along with five types of vortices in the surrounding flow field, are identified for the girder model. Finally, the effects of accessory structures of the bridge model on the VIV responses are also studied. This study contributes to our understanding of the unsteady flow dynamics and VIV mechanisms of a typical triple-box girder. • VIVs of a triple-box girder model has been reproduced in wind tunnel tests. • The 'dual-frequency' phenomenon was found in flow around the triple-box girder, and it might expand the VIV lock-in region. • The large-scale separated vortices coupled with the structural vibrations to sustain VIV of the triple-box girder. [ABSTRACT FROM AUTHOR]