What is the bluff body?

A bluff body can be defined as a body that, as a result of its shape, has separated flow over a substantial part of its surface. Usually bluff bodies induce flow separation at positions where the velocity at the edge of the boundary layer is higher than the free stream velocity.

Why does flow separate from bluff body?

In particular, the adverse pressure gradient on the top rear portion of the airfoil may become sufficiently strong to produce a separated flow. For a bluff body, the dominant source of drag is pressure drag. For a given frontal area and velocity, a streamlined body will always have a lower resistance than a bluff body.

What is a bluff body of water?

The Ozarks. A bluff is a small, rounded cliff that usually overlooks a body of water, or where a body of water once stood.

What is bluff body and its applications?

Flow past a bluff body has a considerable significance in many engineering applications such as bridges, offshore structures, buildings, cooling towers, petroleum pipelines in cross flow, and heat exchanger tubes. The frequency and amplitude of vibrations are the most significant parameters of flow-induced motions.

What is wake in aerodynamics?

The wake is the region of disturbed flow (often turbulent) downstream of a solid body moving through a fluid, caused by the flow of the fluid around the body. Parachutes deployed into wakes suffer dynamic pressure deficits which reduce their expected drag forces.

What is the difference between streamlined body and bluff body?

A streamlined body is defined as that body whose surface is aligned with the streamlines, when the body is placed in the flow. A bluff body is defined as that body whose surface is not aligned with the stream-lines, when placed in the flow. • Thus, the body offers lesser resistance in terms of Viscous/Frictional drag.

How do I find my Strouhal number?

The Strouhal number is defined as St = fstD/U, where fst is the vortex shedding frequency (or the Strouhal frequency) of a body at rest, D is the diameter of the circular cylinder and U is the velocity of the ambient flow.

What circular cylinder is Strouhal number?

The Strouhal number of a stationary tube or circular cylinder is a function of Reynolds number but less of surface roughness and freestream turbulence, see Figure 2.

Whats a no wake zone?

A “no-wake zone” is an area where vessels are expected to travel at slow (idle) speeds to minimize the wake. Public safety is often the primary reason for establishing and enforcing no-wake areas, and that is why most no-wake zones are near boat launches, docks or residential areas.

What is wake and bluff body?

Bluff body flows are characterized by flow separation which produces a region of disturbed. flow behind, i.e. the wake. Within the near-wake various forms of flow instabilities, both. convective and absolute, may be triggered and amplified.

Why are Reynolds numbers so high in naval bluff body flows?

In practical naval bluff body flows, Reynolds numbers are usually high and in a range where disturbances are massively amplified through instability mechanisms. This leads to both turbulence, i.e. multi-scale, random, three-dimensional motion, and the generation and shedding of large coherent vortex structures.

What is a common feature of bluff body flows?

A common feature of bluff body flows is that they are complex and often difficult to predict. In practical naval bluff body flows, Reynolds numbers are usually high and in a range where disturbances are massively amplified through instability mechanisms.

What is the difference between bluff body aerodynamics and bluff body hydrodynamics?

Clearly bluff body aerodynamics and bluff body hydrodynamics are closely related but in the naval context the presence of an air/water interface and surface waves introduce additional phenomena that are absent in aerodynamic flows. A common feature of bluff body flows is that they are complex and often difficult to predict.

Are bluff body wakes three-dimensional?

The general conclusion reached from studies such as the one outlined above is that at high Reynolds numbers three-dimensionally is a very important feature of bluff body wakes, even for wakes generated from nominally two-dimensional geometries.