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Fluid Dynamics and Its Applications
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Physics Textbooks Boundless Physics Fluid Dynamics and Its Applications Other Applications
Physics Textbooks Boundless Physics Fluid Dynamics and Its Applications
Physics Textbooks Boundless Physics
Physics Textbooks
Physics
Concept Version 8
Created by Boundless

Turbulence Explained

It is imperative to consider turbulent flow when designing many things such as airplanes, medical equipment, heat exchangers, and bridges.

Learning Objective

  • Predict if flow will be laminar or turbulent


Key Points

    • For low velocity, flow in a smooth tube will be laminar.
    • At higher velocities or if there are obstructions, the flow turns turbulent.
    • Turbulent flow is very chaotic, with rapid variations in velocity and pressure.

Terms

  • laminar

    Of fluid motion, smooth and regular, flowing as though in different layers.

  • turbulent

    Being in, or causing, disturbance or unrest.

  • streamlined

    Designed to offer little resistance to the flow of fluid, especially by having sleek, graceful lines.


Example

    • Modern heat exchangers have specially designed tubes which encourage turbulent flow for better mixing and heat transfer.

Full Text

It is possible to predict if flow will be laminar or turbulent. At low velocity, flow in a very smooth tube or around a smooth, streamlined object will be laminar. At high velocity, even the flow in a smooth tube or around a smooth object will experience turbulence. However, between low and high velocity, flow is more difficult to predict. In fact, at intermediate velocities, flow may oscillate back and forth indefinitely between laminar and turbulent.

An occlusion (narrowing) of an artery, such as shown in , is likely to cause turbulence because of the irregularity of the blockage, as well as the complexity of blood as a fluid. Turbulence in the circulatory system (such as aneurysms, or ballooning of arteries) is noisy and can sometimes be detected with a stethoscope (such as when measuring diastolic pressure in the upper arm's partially collapsed brachial artery). These turbulent sounds, at the onset of blood flow when the cuff pressure becomes sufficiently small, are called Korotkoff sounds. Heart murmurs, consistent with their name, are sounds produced by turbulent flow around damaged and insufficiently closed heart valves. Another method of detecting this type of turbulence is ultrasound, used as a medical indicator in a process analogous to Doppler-shift radar (used to detect storms).

Turbulent Flow in an Artery

Flow is laminar in the large part of this blood vessel and turbulent in the part narrowed by plaque, where velocity is high. In the transition region, the flow can oscillate chaotically between laminar and turbulent flow.

Turbulence manifests in other areas, with varying causes. During an airplane flight, for example, the turbulence experienced is due to the mixing of warm and cold air in the atmosphere, causing the airplane to shake. The mixing currents in oceans creates a similar effect.

The phenomenon of turbulent air flow must be accounted for in many applications. For example, race cars are unable to follow each other around fast corners because the leading car creates turbulent air flow in its wake (this can lead to under-steering).

Industrial equipment, such as pipes, ducts, and heat exchangers are often designed to induce the flow regime of interest (laminar or turbulent). When flow is turbulent, particles exhibit additional transverse motion. This enhances the rate of energy and momentum exchange between them, increasing the heat transfer. Turbulent flow is thus desirable in applications where a relatively cool fluid is mixed with a warmer fluid to reduce the temperature of the warmer fluid.

It is imperative to take into account turbulent flow when designing certain structures, such as a bridge support, as shown in . In the late summer and fall, when river flow is slow, water flows smoothly around the support legs. In the spring, when the flow is faster, the flow may start off laminar but it is quickly separated from the leg and becomes turbulent. The bridge supports must be designed so that they can withstand the turbulent flow of the water in the spring.

Longtown Bridge

Turbulent flow is visible around the bridge supports of the Longtown bridge.

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