Influence of bed proximity on the three-dimensional characteristics of the wake of a sharp-edged bluff body

Abstract

The gap flow effect in a wake is investigated to develop an improved picture of the formation of fluid structures via a numerical simulation of flow past a bluff body with two different clearances from the bed. These two cases are compared with the no-gap case which is considered as a reference case. The transient three-dimensional Navier-Stokes equations are numerically solved using a finite volume approach with the detached eddy simulation as the turbulence model. The effect of the free surface is included in the model by using the volume of fluid method. The fluid structures that are generated in the wake are identified using the λ2-criterion. It is found that the gap flow influences the formation of various types of fluid structures in the wake region. The horseshoe vortex appears to be attenuated as the gap size increases. The turbulent structures at the core of the wake appear to be disorganized and have the ability to extend further in the transverse direction in the absence of the horseshoe vortex. A new structure is identified in the wake flow when the gap size exceeds a threshold value. This structure acts to enhance the positive wall-normal velocity and accelerate the restoration of the free surface to its original position at shorter distances downstream of the bluff body. The lateral entrainment to the wake region is also enhanced as the gap is introduced in the wake flow.

Computational Investigation of the Effect of the Aspect Ratio on Secondary Currents in Open Channels

“…Furthermore, successive grids were compared to determine whether or not there was a change in the mean characteristics. The results for the mean flow quantities and cell independence study were very similar to those reported earlier in [8], [21], [22] and are not repeated here for brevity. In this study, the total number of cells used for the computation is 1.3 and 8.7 million elements for AR = 1 and 12, respectively.…”

Turbulent Structures in Gap Flow

“…A distinguished structure at the near-bed location is generated when the gap is introduced in the wake flow. The extent and strength of this structure increase with the increase of the size of the gap [7]. The interaction between this structure and the other fluid structures boosts the vertical velocity component that is normal to the bed.…”

“…This type of flow is often encountered in engineering applications, e.g., the airflow around solar panels, flow around vehicles, and the cooling of electronic components. Many experimental and computational studies have been carried out with sharp-edged plate, circular and square cylinders as a bluff body to investigate the influence of the gap size on the wake characteristics, such as works of Shinneeb and Balachandar [1], Shinneeb et al, [2], Martinuzzi et al, [3], Bosch et al, [4], Essel et al, [5] and Nasif et al, [6,7]. In these studies, the bluff bodies were oriented horizontally and vertically at different heights above the bed.…”

“…However, these fluid structures lose their regularity and two structures merge into one if the gap is introduced in a wake flow. The asymmetry and interaction between the fluid structures increase as the gap size increases [7]. A distinguished structure at the near-bed location is generated when the gap is introduced in the wake flow.…”

Noise emitted from a generic side-view mirror with different aspect ratios and inclinations

“…Aerodynamics and aeroacoustics of standard bluff bodies are subject of considerable interest owing to their widespread applications in science and engineering. [1][2][3][4][5][6][7][8] For example, during vehicle design and development stages, evaluating the noise generated due to the wind and its propagation into the cabin becomes critical as the wind-induced noise is a dominant noise source at speeds greater than 100 km/h. Frequent exposure to wind-induced noise can lead to driver fatigue, which for longer journeys may impact driver's safety at high noise levels, whereas, at lower levels of noise, it can impact the degree of vehicle refinement.…”