What causes pressure in form drag?

In summary: L/Fluid/node116.htmlIn summary, the article discusses how the pressure goes up in the rear of a ball when there is less circulation. This is due to the viscous nature of air.
  • #1
JTC
100
6
Consider a ball flying through the air.

When there is turbulence, and the flow separates, say on a SMOOTH ball, then in the rear, there is circulation in the wide wake. There is pressure on the front, but no pressure on the rear due to the fact that the fluid is "busy" circulating around. So there is form drag.

When there is NO turbulence (or little) and the flow does not separate as early, say on a golf ball, then there is LESS circulation in the rear in the smaller wake.

So my question is: What gives rise to the pressure in the rear, when there is an "annealed" or "healed" flow (when the dimples on the golf ball make the wake smaller).

Where is the higher pressure coming from in the rear to match the pressure at the front end?

(I am not asking about the dimples on golf balls. I am only asking why the pressure goes up in the rear. Yes, I know there is a smaller wake but that does not explain why the pressure goes up.)
 
Last edited:
Engineering news on Phys.org
  • #3
  • #4
BvU said:
https://www.scientificamerican.com/article/how-do-dimples-in-golf-ba/

In other words... Why is there lower pressure in the circulation? I would guess Bernoulli's equation in in the slower flow, but Bernoulli should not apply
do to the viscous nature.

And why is the pressure higher without the circulation?

The article falls flat right where I want the answer.
 
  • #6
JTC said:
Bernoulli should not apply due to the viscous nature.
are you saying Bernoulli does not apply to air ?
 
  • #7
BvU said:
are you saying Bernoulli does not apply to air ?

Well, this is where all the confusion for me is.

I would think that no, it does not. But if one is studying effects induced by viscosity, then Bernoulli cannot be used to justify something. I think.
 
  • #8
Bernoulli definitely applies (see story about truck and car being pushed towards each other), but not the full extent since there is energy loss.

When I read the Jestocott link or this link, the emphasis is on the size of the wake. But you stll need the pressure in the wake to be lower in order to get that effect of bigger wake ##\Leftrightarrow## more drag.
 
  • Like
Likes Lord Jestocost

1. What is form drag and how does it relate to pressure?

Form drag is a type of drag force that occurs when an object moves through a fluid, such as air or water. It is caused by the pressure difference between the front and back of the object. As the fluid flows around the object, it creates an area of high pressure in front and low pressure behind, causing the object to experience a force in the opposite direction of its motion.

2. What factors contribute to the formation of pressure in form drag?

There are several factors that contribute to the formation of pressure in form drag, including the shape and size of the object, the speed at which it is moving, and the properties of the fluid it is moving through. These factors determine the amount of pressure difference between the front and back of the object, which ultimately affects the magnitude of the drag force.

3. How does pressure in form drag affect the movement of an object?

The pressure in form drag affects the movement of an object by creating a resistance force that opposes its motion. This can lead to decreased speed and increased energy expenditure for the object as it moves through the fluid. In some cases, the pressure in form drag can also cause the object to change direction or experience turbulent flow around its surface.

4. Can pressure in form drag be reduced or eliminated?

While it is not possible to completely eliminate pressure in form drag, it can be reduced by changing the shape or surface texture of the object, or by manipulating the properties of the fluid it is moving through. For example, streamlined shapes and smooth surfaces can decrease the formation of pressure in form drag, while increasing the viscosity of the fluid can also reduce its effects.

5. How does understanding pressure in form drag benefit scientists and engineers?

Understanding pressure in form drag is essential for scientists and engineers in fields such as aerodynamics, hydrodynamics, and fluid mechanics. It allows them to predict and control the movement of objects through fluids, and to design more efficient and streamlined structures that minimize the effects of drag. This knowledge is also crucial for the development of various technologies, such as aircraft, ships, and automobiles.

Similar threads

Golf ball and Tennis ball turbulence
    • Mechanics
Replies
7
Views
3K
Using golf ball dimples to decrease vaccuum drag on motor vehicles and aircraft.
    • Mechanical Engineering
Replies
31
Views
24K
Ridiculously low drag coefficient from OpenFOAM CFD
    • Mechanical Engineering
Replies
1
Views
1K
What phenomenon occurs that reduces drag when a swim cap is applied
    • Mechanical Engineering
Replies
10
Views
2K
Questions involving airflow and pressure around a car
    • Introductory Physics Homework Help
Replies
21
Views
3K
Surface roughness in 2D sinusoidal corrugation
    • Mechanical Engineering
Replies
1
Views
3K
Prevent Flow Separation | Impact on Drag & Efficiency of Cars & Wings
    • General Engineering
Replies
8
Views
7K
Need Help Understanding Turblance / Laminar Flow
    • Mechanical Engineering
Replies
11
Views
3K
Aerodynamics: Drag & Bernoulli in Turbulent Flows
    • Engineering and Comp Sci Homework Help
Replies
6
Views
3K
A question on boundary layers viscosity and air seperating frmo a ball
    • Mechanical Engineering
Replies
12
Views
5K

Hot Threads

Recent Insights

Back
Top