Pressure and normal stress in fluid mechanics

According to one book, these forces include pressure, shear stress, and normal stress. However, Chetan is confused about the difference between normal stress and pressure. After some discussion, it is clarified that normal stress is actually a combination of pressure and viscous stresses, with the latter only coming into play when the fluid is deforming. In summary, surface forces on a fluid cell include pressure, shear stress, and normal stress, with the latter being a combination of pressure and viscous stresses.
  • #1
asteroid21
Hi, everyone.
I am learning fluid mechanics. One book says that for a infinitesimal fluid cell, surface force includes
1) the pressure, which is imposed by the outside fluids surrounding the concerned fluid cell
2) the shear and normal stress, which result in shear deformation and volume change, respectively.

But I think normal stress is pressure. Can anyone help me clarify?
Thank you.
 
Physics news on Phys.org
  • #2
If the fluid is in static equilibrium, then only the pressure contributes. But, if the fluid is deforming, then there are viscous stresses in the fluid over and above the pressure; both go into determining the force per unit area. The overall stress tensor is a linear combination of the pressure (which is isotropic) and the viscous stresses, which, for an incompressible fluid, are not isotropic. The normal stress on an element of area is the sum of the pressure plus the normal viscous stress.

Chet
 

Related to Pressure and normal stress in fluid mechanics

1. What is the difference between pressure and normal stress in fluid mechanics?

Pressure and normal stress are two related but distinct concepts in fluid mechanics. Pressure is a measure of the force exerted on a unit area of a fluid, while normal stress is a measure of the force per unit area that a fluid exerts on a surface. In other words, pressure is the force acting on the fluid, while normal stress is the force that the fluid applies to a surface.

2. How is pressure and normal stress calculated in fluid mechanics?

Pressure is calculated by dividing the force acting on a fluid by the area over which the force is applied. Normal stress is calculated by dividing the force that the fluid exerts on a surface by the area of the surface. Both pressure and normal stress are typically measured in units of force per unit area, such as pascals (Pa) or pounds per square inch (psi).

3. What factors affect pressure and normal stress in fluid mechanics?

There are several factors that can affect pressure and normal stress in fluid mechanics. These include the density and velocity of the fluid, the shape and orientation of the surface the fluid is acting on, and the direction and magnitude of the external forces acting on the fluid. Additionally, the type of fluid (i.e. Newtonian vs. non-Newtonian) can also influence pressure and normal stress.

4. How does pressure and normal stress impact the behavior of fluids?

Pressure and normal stress play a critical role in determining the behavior of fluids. In general, an increase in pressure will cause a fluid to compress and decrease in volume, while a decrease in pressure will cause the fluid to expand and increase in volume. Normal stress also affects the flow of fluids, as it can create friction and resistance between the fluid and surfaces it is in contact with.

5. How is pressure and normal stress used in practical applications?

Pressure and normal stress are important concepts in many practical applications, including hydraulic systems, fluid dynamics, and aerodynamics. In hydraulic systems, pressure is used to transmit force and control the movement of fluids. In fluid dynamics and aerodynamics, pressure and normal stress are key factors in understanding the behavior of fluids and designing efficient systems, such as airplane wings and wind turbines.

Similar threads

I Pressurized containers: Stress distribution and large displacements
    • Mechanics
2
Replies
69
Views
3K
Regarding the pressure at a point in a "rested" fluid
    • Mechanics
Replies
1
Views
1K
I A specific case of an exception to Archimedes' Principle?
    • Mechanics
2
Replies
40
Views
2K
What causes pressure and is it isotropic in a moving fluid?
    • Mechanics
Replies
14
Views
2K
Engineering Normal and Shearing Stress - Combined Loading
    • Engineering and Comp Sci Homework Help
Replies
4
Views
1K
Classical I need some self-contained introductory books on Fluid Mechanics
    • Science and Math Textbooks
Replies
19
Views
3K
"Air Pressure" is not "the weight of the air above you"
    • Mechanics
Replies
27
Views
2K
Some questions about Friction in fluid flow
    • Materials and Chemical Engineering
Replies
16
Views
2K
(Fluids) Difference in stress or pressure between setups?
    • Mechanics
Replies
10
Views
2K
Why does the pressure of a fluid in motion change?
    • Mechanics
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top