Logout Open In App
Open In App
Warning: foreach() argument must be of type array|object, bool given in /var/www/html/web/app/themes/studypress-core-theme/template-parts/header/mobile-offcanvas.php on line 20

Chapter 7: Problem 6

What is the difference between skin friction drag and pressure drag? Which is usually more significant for slender bodies such as airfoils?

Short Answer

Expert verified
Answer: Skin friction drag is caused by the friction between the fluid and the object's surface, while pressure drag is due to the pressure difference resulting from flow separation around the object. For slender bodies like airfoils, skin friction drag is usually more significant due to their streamlined design, which minimizes pressure drag.

Step by step solution

01

Define Skin Friction Drag

Skin friction drag is the resistance caused by the friction between the fluid (such as air) and the surface of a solid object (such as an airfoil) as the fluid flows over the object. It is directly related to the surface's roughness and shear stress experienced by the fluid layer in contact with the surface.
02

Define Pressure Drag

Pressure drag, also known as form drag, is the resistance caused by the pressure difference between the front and the back of an object moving through a fluid. It is dependent on the shape of the object and occurs when the fluid flow separates from the object's surface, creating a region of low pressure behind the object and generating vortices, which result in a net force acting opposite to the direction of motion.
03

Compare Skin Friction Drag and Pressure Drag

Skin friction drag is a result of the fluid's friction on the object's surface, while pressure drag is caused by the pressure difference and flow separation due to the object's shape. Both types of drag act in the direction opposite of the fluid flow and contribute to the total drag force on the object.
04

Skin Friction Drag and Pressure Drag on Slender Bodies

For slender bodies such as airfoils, the skin friction drag is usually more significant than pressure drag. This is because the streamlined shape of airfoils is designed to minimize pressure drag by maintaining a smooth flow of the fluid around the object, reducing flow separation, and thus, the pressure difference. However, the surface area exposed to the fluid flow is still significant, leading to a relatively higher contribution of skin friction drag to the total drag force.
05

Conclusion

In conclusion, the difference between skin friction drag and pressure drag lies in their causes. Skin friction drag is caused by the friction between the fluid and the object's surface, while pressure drag is due to the pressure difference resulting from flow separation around the object. For slender bodies like airfoils, skin friction drag is usually more significant due to their streamlined design, which minimizes pressure drag.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Consider a refrigeration truck traveling at \(70 \mathrm{mph}\) at a location where the air temperature is \(80^{\circ} \mathrm{F}\). The refrigerated compartment of the truck can be considered to be a 9 -ft-wide, 7 -ft-high, and 20 -ft-long rectangular box. The refrigeration system of the truck can provide 3 tons of refrigeration (i.e., it can remove heat at a rate of $600 \mathrm{Btu} / \mathrm{min}$ ). The outer surface of the truck is coated with a low-emissivity material, and thus radiation heat transfer is very small. Determine the average temperature of the outer surface of the refrigeration compartment of the truck if the refrigeration system is observed to be operating at half the capacity. Assume the airflow over the entire outer surface to be turbulent and the heat transfer coefficient at the front and rear surfaces to be equal to that on side surfaces. For air properties evaluations, assume a film temperature of \(80^{\circ} \mathrm{F}\). Is this a good assumption?

Water vapor at \(250^{\circ} \mathrm{C}\) is flowing with a velocity of $5 \mathrm{~m} / \mathrm{s}\( in parallel over a \)2-\mathrm{m}$-long flat plate where there is an unheated starting length of \(0.5 \mathrm{~m}\). The heated section of the flat plate is maintained at a constant temperature of \(50^{\circ} \mathrm{C}\). Determine \((a)\) the local convection heat transfer coefficient at the trailing edge, \((b)\) the average convection heat transfer coefficient for the heated section, and \((c)\) the rate of heat transfer per unit width for the heated section.

In flow across tube banks, how does the heat transfer coefficient vary with the row number in the flow direction? How does it vary in the transverse direction for a given row number?

Air \(\left(1 \mathrm{~atm}, 5^{\circ} \mathrm{C}\right)\) with a free-stream velocity of \(2 \mathrm{~m} / \mathrm{s}\) flows in parallel with a stationary thin \(1-\mathrm{m} \times 1-\mathrm{m}\) flat plate over the top and bottom surfaces. The flat plate has a uniform surface temperature of $35^{\circ} \mathrm{C}\(. Determine \)(a)\( the average friction coefficient, \)(b)$ the average convection heat transfer coefficient, and (c) the average convection heat transfer coefficient using the modified Reynolds analogy, and compare with the result obtained in \((b)\).

Air at \(25^{\circ} \mathrm{C}\) flows over a 5 -cm-diameter, \(1.7-\mathrm{m}\)-long smooth pipe with a velocity of $4 \mathrm{~m} / \mathrm{s}\(. A refrigerant at \)-15^{\circ} \mathrm{C}$ flows inside the pipe, and the surface temperature of the pipe is essentially the same as the refrigerant temperature inside. The drag force exerted on the pipe by the air is (a) \(0.4 \mathrm{~N}\) (b) \(1.1 \mathrm{~N}\) (c) \(8.5 \mathrm{~N}\) (d) \(13 \mathrm{~N}\) (e) \(18 \mathrm{~N}\) (For air, use $\nu=1.382 \times 10^{-5} \mathrm{~m}^{2} / \mathrm{s}, \rho=1.269 \mathrm{~kg} / \mathrm{m}^{3}$ )
See all solutions

Recommended explanations on Physics Textbooks

Famous Physicists

Read Explanation

Wave Optics

Read Explanation

Oscillations

Read Explanation

Linear Momentum

Read Explanation

Electricity

Read Explanation

Engineering Physics

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free