What is boundary layer turbulence?

For higher Reynolds numbers, the boundary layer is turbulent and the streamwise velocity is characterized by unsteady (changing with time) swirling flows inside the boundary layer. The external flow reacts to the edge of the boundary layer just as it would to the physical surface of an object.

Why does a boundary layer become turbulent?

Boundary layer flow over a wing surface begins as a smooth laminar flow. As the flow continues back from the leading edge, the laminar boundary layer increases in thickness. At some distance back from the leading edge, the smooth laminar flow breaks down and transitions to a turbulent flow.

How does a turbulent boundary layer produce world?

How does a turbulent boundary layer produce swirls? Explanation: For a turbulent boundary layer the fluid moves in different direction producing swirls. It produces swirls due to the presence of eddies. The smooth laminar boundary layer flow breaks down and transforms to a turbulent flow.

How does surface roughness affect turbulence?

For the same flow over a rough surface Fig. 1 (b), the roughness increases flow instability close to the wall which can lead to increased localised turbulence disrupting the viscous sublayer, thereby generating the roughness sublayer and affecting pressure drop and heat transfer.

How do turbulent boundary layers help reduce levels of form drag?

pressure drag is reduced by turbulent flow by delaying boundary layer separation, but this increases the skin-friction drag due to higher shear stresses at the wall.

What do you mean by laminar and turbulent boundary layers What is laminar sublayer?

The laminar sublayer, also called the viscous sublayer, is the region of a mainly-turbulent flow that is near a no-slip boundary and in which viscous shear stresses are important. As such, it is a type of boundary layer.

What is the main reason why a laminar boundary layer has less drag than a turbulent boundary layer?

A laminar boundary layer has less momentum near the wall than a turbulent boundary layer, as shown in figure 4, because turbulence is a very effective mixing process. More importantly, turbulent transport of momentum is very effective at replenishing the near-wall momentum.

How the boundary layer is developed in a pipe for turbulent flow?

A boundary layer is formed at the wall and its thickness increases with increased distance downstream from the pipe inlet. The core flow which has not yet been affected by friction is accelerated until, after a sufficient distance, the boundary layer has grown to its full width.

How does the surface roughness affect the boundary layer?

In many situations, turbulent boundary layers develop over surfaces that are hydrodynamically rough over at least some part of their length. The major impact of surface roughness is to perturb the wall layer in such a way as to lead, in general, to an increase in the wall shear stress.

Does roughness increase turbulence?

[18] noted that surface roughness significantly enhances the levels of the turbulence kinetic energy, and turbulence diffusion in a way that depends on the specific geometry of the roughness elements.

How turbulence phenomenon is useful?

The turbulent events are associated with coherent flow structures such as eddies and turbulent bursting, and they play a critical role in terms of sediment scour, accretion and transport in rivers as well as contaminant mixing and dispersion in rivers and estuaries, and in the atmosphere.

How does turbulence affect drag?

Turbulent flow creates more friction drag than laminar flow due to its greater interaction with the surface of the airplane.