Narrow Results

This paper provides the impact of roughness on the hydrodynamic behavior of the fluid over a convex-shape grooved cylinder by examining the shape and amplitude of the groove influence on the average flow rate. Direct numerical investigations of two-dimensional flow around a convex-shape grooved cylinder are performed at Reynolds number up to 100. A Reynolds number up to 40 corresponds to laminar flow in a stable state presenting the creeping and symmetry regimes and Re of 100 corresponds to laminar unstable flow presenting pure Karman vortex street flow regime. The number of grooves is set at 10, 20 and 30, uniformly spread around the periphery of the cylinder, with three different wave amplitudes of 1/50, 1/25 and 1/12.5, for each geometry. The numerical algorithm applied in this investigation is based on the finite volume method. The obtained results are compared with the smooth cylinder at the same Reynolds number, that latter shows excellent agreement with the available data in the literature. The forces acting on the cylinder are seen to be reduced by the presence of the grooves; this reduction is more significant with increasing groove amplitude, especially at a high Reynolds number. At Reynolds number equal 100, when the groove number and wave amplitude are set to 10, 1/12.5, respectively, the drag coefficient is lowered by about 10%, while the lift coefficient is reduced by around 25%.

When air passes through the hangar of a frigate, the unstable airwake appears in the rear of the hangar, which may significantly increase the workload of the ship-borne helicopter pilot. Therefore, there must be a profound understanding of the characteristics of the airwake. In this paper, the airwake was numerically studied by using the Improved Delayed Detached-Eddy Simulation (IDDES) turbulence model on structured grids. The flow fields of the different simplified frigate afterbody models, consisting of hangar and flight deck, were compared regarding the size of the recirculation zone. A parametric study was conducted by varying the hangar length to find the optimal afterbody model with minimal recirculation zone behind the hangar. The results show that the size as well as the location of the recirculation zone are significantly affected by the hangar length, and the optimal afterbody model has been obtained.

The high-speed airflow generated by ultra-high-speed elevators causes significant aerodynamic force, which seriously reduces the comfort and safety of passengers. First, a multi-parameter general model of ultra-high-speed elevator was established, and the three-dimensional numerical simulation of incompressible flow in the ultra-high-speed elevator was simulated. The correctness of the model and method was verified by experiments and grid-independence analyses. On this basis, the variation in the aerodynamic forces and the pressure in the hoistway was analyzed. Finally, the influence of different hoistway structures and parameters of ventilation holes on the aerodynamic forces and hoistway pressure were analyzed. The results showed that the opening of ventilation holes significantly reduced the aerodynamic forces and hoistway pressure for most of the period of the car’s operation period, but both the aerodynamic forces and hoistway pressure showed a sudden increase–decrease process. The aerodynamic forces and hoistway pressure were highly sensitive to changes in the hoistway blockage ratio, the cross-sectional area of the ventilation hole, and the position of the ventilation hole. When a pair of ventilation holes were opened, those in the middle of the hoistway reduced aerodynamic problems in the hoistway to the greatest extent. The increase in the connection angle between the ventilation hole and the hoistway eliminated the low-speed recirculation zone at the ventilation hole and increased the total volume of exhaust air at the ventilation hole.

Disrupted flow initiates and aggravates intimal thickening in the end-to-side (ETS) coronary artery bypass grafting (CABG), which may lead to failure. To enhance the post-intervention hemodynamics, the geometry is either optimized or totally reconfigured. Majority of configurations proposed by researchers have not suited CABG surgery, for they entailed rigorous manipulation on conventional grafts in situ, which was neither swift nor straightforward. The aim of the present study is, thus, to introduce a slight, yet effective, modification to a conventional ETS CABG configuration, and numerically investigate its effects on updated hemodynamic and structural environment, anticipating the longevity of proposed configuration and CABG success. This fairly simple modification may easily be made positioning a pre-designed anastomotic device between the bed of host artery in the conventional ETS CABG and its surrounding tissues. Conducting comprehensive numerical simulations, performance of the proposed configuration was assessed using idealized and patient-specific geometries of the conventional ETS CABG. Blood flow was simulated in a conventional and an updated CABG configuration considering 2-way fluid–structure interaction. Results revealed that, although the proposed configuration may induce higher structural stresses in vessels walls, it may improve important hemodynamic metrics such as wall shear stress gradient, oscillatory shear index, and relative residence time on host artery bed reducing disruption of flow. This study may also set the stage for design engineers and regulatory officials to evolve ETS CABG toward more hemodynamics-friendly approaches. Further in vitro, preclinical, and clinical experiments are, yet, entailed to accomplish ideal designs of procedural guidelines/grafts.

The dispersion of point and nonpoint source pollutants may be complicated by the existence of coastal geographical features such as headlands. When coastal flow passes a headland on the coastal line, a recirculation zone will be formed as the flow separates at the headland toe. The experimental investigation was carried out in a purpose-built flume, located at the Manchester Tidal flow Facility (MTF). From the experiments, if pollutant is discharged at different locations around the perimeter of a headland, the potential of pollutant trapping around the headland and its generated recirculation zone will change accordingly. This study investigates the characteristics of pollutant dispersion in the region around the headland perimeter. Effective pollutant dispersion at the recirculation zone will be crucial to maintain the water quality of the region.