Secondary flow

In that case, the secondary flow usefully spotlights the effects of complicated real-world terms neglected in those approximated equations.

For instance, the consequences of viscosity are spotlighted by secondary flow in the viscous boundary layer, resolving the tea leaf paradox.

Interference by surface roughness elements such as terrain, waves, trees and buildings cause drag on the wind and prevent the air from accelerating to the speed necessary to achieve balanced flow.

In a region of high pressure (an anticyclone) the secondary flow includes a slow, widespread descent of air from mid altitudes toward ground level, and then outward across the isobars.

This descent causes a reduction in relative humidity and explains why regions of high pressure usually experience cloud-free skies for many days.

The viscous secondary flow near the Earth's surface converges toward the center of the cyclone, ascending in the eyewall to satisfy mass continuity.

As the secondary flow is drawn upward the air cools as its pressure falls, causing extremely heavy rainfall and releasing latent heat which is an important driver of the storm's energy budget.

Their fluid motion is similar to tropical cyclones but on a much smaller scale so that the Coriolis effect is not significant.

This gradient, coupled with the slower speed of the air near the earth's surface, causes a secondary flow toward the center of the tornado or dust devil, rather than in a purely circular pattern.

The secondary flow is toward the center of the tornado or dust devil, and is then drawn upward by the significantly lower pressure several thousands of feet above the surface in the case of a tornado, or several hundred feet in the case of a dust devil.

Tornadoes can be very destructive and the secondary flow can cause debris to be swept into a central location and carried to low altitudes.

The accumulation of dust then accompanies the secondary flow upward into the region of intense low pressure that exists outside the influence of the ground.

The slower speed of the water in the boundary layer is unable to balance the pressure gradient.

The boundary layer spirals inward and sweeps the heavier solids into a neat pile in the center of the bowl or cup.

With water circulating in a bowl or cup, the primary flow is purely circular and might be expected to fling heavy particles outward to the perimeter.

Centripetal forces are necessary for the curved path of each parcel of water, which is provided by the pressure gradient.

On the floor of the river bed the secondary flow sweeps sand, silt and gravel across the river and deposits the solids near the convex bank, in similar fashion to sugar or tea leaves being swept toward the center of a bowl or cup as described above.

Modelling the flow enables blade, vane and end-wall surfaces to be shaped to reduce the losses.

If the deflection angle, e, between the guide vanes is small, the magnitude of the secondary vorticity is represented as

Thrust-producing flow which passes through an engines thermal cycle is called primary airflow.

Airflow through a propeller or a turbomachine fan is called secondary flow and is not part of the thermal cycle.

[15] This use of secondary flow reduces losses and increases the overall efficiency of the propulsion system.

Concorde, North American XB-70 and Lockheed SR-71 used ejector-type supersonic nozzles which had a secondary flow obtained from the inlet upstream of the engine compressor.