How does viscosity affect turbulent flow?

The greater the viscosity of a fluid, the greater the value of R. Turbulence greatly increases R, whereas increasing the diameter of a tube decreases R. If viscosity is zero, the fluid is frictionless and the resistance to flow is also zero.

How does viscosity affect boundary layer?

Viscous force is dominant relative to inertial force in the boundary layer, so energy dissipation near the tank wall causes impact energy to decrease due to internal viscous friction. Therefore impact pressure is smaller in computational model with boundary layer grid.

Why do the flows become turbulent at high Reynolds numbers?

The viscous regions in high Reynolds number flows are dominated by turbulence. Instability in the shear layer creates turbulent fluctuations of flow-field properties. That is why these models did not become famous for predicting flows involving shear and mixing layers and detached flows.

What does a high turbulent viscosity mean?

The turbulent transfer of momentum by eddies giving rise to an internal fluid friction, in a manner analogous to the action of molecular viscosity in laminar flow, but taking place on a much larger scale. It is greater for flows with more turbulence.

What happens when flow around car becomes more turbulent?

The following car is badly affected by that turbulence because there is no clean air to flow in a smooth laminar fashion over its aero surfaces, so it loses downforce. It cannot put power down as effectively, and it loses track adhesion, so overtaking becomes almost impossible.

How does viscosity affect boundary layer thickness?

Thus the inertial to viscous force raitio will increase. Consequently the viscous effect imposed on fluid flow due to the effect of the surface (no slip BC) over which flow is taking place will be confined to smaller BL thickness. Obviously by increasing velocity on flat plate boundary layer decreases.

What is turbulent boundary layer?

A boundary layer may be laminar or turbulent. A laminar boundary layer is one where the flow takes place in layers, i.e., each layer slides past the adjacent layers. A turbulent boundary layer on the other hand is marked by mixing across several layers of it.

What is turbulent viscosity?

The turbulent or eddy viscosity μt is defined by the following relationship: (2) є The field distribution of the turbulence kinetic energy k and its dissipation rate є (a measure of turbulence length scale) are obtained from the solution of the relevent transport equations.

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.

How does a turbulent boundary layer produce swirls?

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.

What is the boundary layer of a turbulent flow?

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.

What is the velocity gradient in the viscous sublayer?

The viscous sublayer covers the innermost 10–20\% of the turbulent boundary layer y /δ = 0.1–0.2. Despite its low thickness, about 70\% of the velocity gradient is found in this region. The local mean velocity in this region is a function of the wall shear stress, fluid density, kinematic viscosity, and distance from the wall.

What is the boundary layer for lower Reynolds numbers?

For lower Reynolds numbers, the boundary layer is laminar and the streamwise velocity changes uniformly as one moves away from the wall, as shown on the left side of the figure.

What are the two processes involved in the formation of turbulence?

The first one is the presence of low-speed streaks that develop in and from the viscous sublayer, the region very close to the bed where viscous forces dominate due to the very low velocity of the flow. The second process is the ejection of fluid from these low-speed streaks into the fast-flowing flow higher up in the turbulent boundary layer.