Flow in Noncircular Ducts

Under Reynolds number for shapes like squares, rectangular or annular ducts the feature dimension for internal flow situations is taken to be the hydraulic diameter, D_H, described as 4times the cross-sectional area, separated by the wetted perimeter. For instance, the wetted perimeter for a channel is the total perimeter of all channel walls that are in connection with the flow. This denotes the length of the water uncovered to air is not contained in the wetted perimeter.

Regarding flow in a wide duct, for a fluid moving between two plane parallel surfaces where the width is much superior than the space between the plates, then the characteristic dimension is twice the distance between the plates.

Flow in Wide Duct and Open Channel

And when it comes to flow in an open channel, for flow of liquid with a free surface, the hydraulic radius must be resolved. This is the cross-sectional part of the channel separated by the wetted perimeter. And for a semi-circular channel, it is half the radius. For a rectangular channel, the hydraulic radius is the cross-sectional part separated by the wetted perimeter. After this some texts use a attribute dimension that is 4 times the hydraulic radius whereas others use the hydraulic radius as the characteristic length-scale with consequently different values of Re for transition and turbulent flow.

Object and Sphere in a Fluid

The Reynolds number for an object in a fluid called the particle Reynolds number and often specified as Rep, is essential when thinking about the nature of flow around that grain, whether or not vortex shedding will happen and its fall velocity. In the case of a sphere in a fluid, the characteristic length-scale is the diameter of the sphere and the characteristic velocity is that of the sphere relative to the fluid some distance away from the sphere. The density and the viscosity are those belonging to the fluid.

The stable state of features of flow in noncircular ducts both with triangular and square cross sections has been examined experimentally. The field is anxious about the effects of corner ribs fitted to the ducts on the nature of the flow. The research is carried out with the hydraulic diameter based Reynolds numbers ranging from 185 to 15,000 and include due injection for flow visualization and pressure drop measurements in the ducts. The corner ribs those without and with ducts were studied to differentiate.

Questions:

• What is Flow in Noncircular Ducts?
• State the role of flow noncircular ducts.