How is the displacement thickness in boundary layer analysis defined?a...
Displacement Thickness in Boundary Layer Analysis
The correct answer for the definition of displacement thickness in boundary layer analysis is option 'C', which states that it is the distance measured perpendicular to the boundary by which the free stream is displaced on account of the formation of the boundary layer. To understand this concept in detail, let's break it down:
Boundary Layer
Before discussing the displacement thickness, it is important to understand what a boundary layer is. In fluid dynamics, a boundary layer refers to the thin layer of fluid adjacent to a solid surface. It is characterized by a gradual transition from the no-slip condition at the surface to the faster-moving free stream flow away from the surface.
Displacement Thickness
The displacement thickness is a measure of the distance by which the free stream flow is displaced due to the presence of the boundary layer. It represents the additional distance that the fluid particles have to travel in order to flow over the surface as compared to the hypothetical case of flow without a boundary layer.
Formation of Boundary Layer
As a fluid flows over a solid surface, the friction between the fluid and the surface slows down the fluid particles in the immediate vicinity of the surface. This creates a velocity gradient within the fluid, with the velocity being zero at the surface and gradually increasing towards the free stream velocity away from the surface.
Explanation of Option 'C'
Option 'C' states that displacement thickness is the distance measured perpendicular to the boundary by which the free stream is displaced on account of the formation of the boundary layer. This means that as the fluid flows over the surface, the presence of the boundary layer causes the fluid to be displaced perpendicular to the surface. This displacement is measured by the displacement thickness.
Significance of Displacement Thickness
The displacement thickness is an important parameter in boundary layer analysis as it affects the overall flow characteristics. It plays a crucial role in determining the total drag force experienced by a body immersed in a fluid flow. The displacement thickness represents the additional distance the fluid has to travel, which results in a reduction in the effective area available for the fluid to flow through. This reduction in effective area leads to an increase in the drag force.
In conclusion, the displacement thickness in boundary layer analysis is the distance measured perpendicular to the boundary by which the free stream is displaced on account of the formation of the boundary layer. It represents the additional distance that the fluid particles have to travel over the surface due to the presence of the boundary layer.
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