Drag Forces in External Flows — Lesson 2

When we swim under water, we are trying to overcome the resistance offered by the water. Similarly, we experience air resistance when riding a bicycle on the road.

In most engineering applications involving external flows, the solid object moving through the fluid has to overcome this fluid resistance during its motion. For example, an aircraft uses the power generated by burning aviation fuel to overcome air resistance. This aerodynamic resistance force is called the fluid drag.

Space shuttles are sometimes transported on the backs of large aircraft to conduct in-flight tests. During this transport, the shuttle tails are covered using the “Shuttle Tail Cone” (as shown in the following image) to reduce aerodynamic drag.

In this lesson, we will learn what this drag force is and how it affects external fluid flows. We will understand the effect of shape on fluid drag and discuss “streamlining,” which has influenced how our cars, planes, trains and even submarines look today. Finally, we will learn about the effect of fluid velocity on drag estimations.

Alternate video link.

Here are the corresponding handout slides for this lesson.