Profile Drag and Pressure Drag?

In summary, profile drag and pressure drag are both sources of drag in aerodynamics. Profile drag is caused by the separation of the boundary layer from the trailing edge of an airfoil, while pressure drag is a result of the adverse pressure causing the boundary layer to separate. The two are closely related and often used together to calculate aerodynamic forces and drag.
  • #1
kevjcarvalho
42
0
Profile Drag and Pressure Drag?

Can someone please tell me the difference between profile drag and pressure drag if there is one??.
 
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  • #2


Try Google, this is very basic. If you don't get stuck there, repost here and I'll help you.
 
  • #3


I tried but they are telling me that profile drag is skin friction and pressure drag...the thing is i read the following line in raymer
' For many aerodynamic calculations, it has been traditional to separate the airfoil into its thickness distribution and zero thickness camber line. The former provides the major influence on the profile drag, while the latter provides the major influence on lift and induced drag'
The thing if pressure drag is part of profile drag and since it is due to separation, shouldn't thickness distribution also change lift, since if pressure drag changes, pressure distribution changes and hence lift changes. Someone told me that profile drag is due to frontal area only, the stagnation part. Is this true?. Thanks.
 
  • #4


kevjcarvalho said:
I tried but they are telling me that profile drag is skin friction and pressure drag...the thing is i read the following line in raymer
' For many aerodynamic calculations, it has been traditional to separate the airfoil into its thickness distribution and zero thickness camber line. The former provides the major influence on the profile drag, while the latter provides the major influence on lift and induced drag'
The thing if pressure drag is part of profile drag and since it is due to separation, shouldn't thickness distribution also change lift, since if pressure drag changes, pressure distribution changes and hence lift changes. Someone told me that profile drag is due to frontal area only, the stagnation part. Is this true?. Thanks.

Addressing your Raymer question specifically, zero thickness camber line is applied in thin airfoil theory and it surprisingly gives good results without accounting for thickness or viscous effects. The reason is that thickness tends to increase the lift slope while viscous effects decrease it and the resulting errors tend cancel each other out.

So then the two are used as Raymer says- airfoil thickness distribution provides the data for thickness and viscous effects complimented with thin airfoil theory for lift and induced drag absent of thickness & viscous effects.
 
  • #5


kevjcarvalho said:
I tried but they are telling me that profile drag is skin friction and pressure drag...the thing is i read the following line in raymer
' For many aerodynamic calculations, it has been traditional to separate the airfoil into its thickness distribution and zero thickness camber line. The former provides the major influence on the profile drag, while the latter provides the major influence on lift and induced drag'
The thing if pressure drag is part of profile drag and since it is due to separation, shouldn't thickness distribution also change lift, since if pressure drag changes, pressure distribution changes and hence lift changes. Someone told me that profile drag is due to frontal area only, the stagnation part. Is this true?. Thanks.

Read carefully.
The airfoil is separated into thickness distribution and camber. This thickness distribution, then would be symmetrical abd won't have any effect on lift (atleast not much significant effect).
 
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  • #6


Thats true, but what is profile drag. Is it pressure drag, skin friction drag, or drag due to frontal area??
 
  • #7


kevjcarvalho said:
Thats true, but what is profile drag. Is it pressure drag, skin friction drag, or drag due to frontal area??

It's pressure and friction drag.
 
  • #8


dtango said:
Addressing your Raymer question specifically, zero thickness camber line is applied in thin airfoil theory and it surprisingly gives good results without accounting for thickness or viscous effects. The reason is that thickness tends to increase the lift slope while viscous effects decrease it and the resulting errors tend cancel each other out.

So then the two are used as Raymer says- airfoil thickness distribution provides the data for thickness and viscous effects complimented with thin airfoil theory for lift and induced drag absent of thickness & viscous effects.

Great post.
 
  • #9


Cyrus said:
Great post.

Haha thanks. I happened to have my Phillips, Anderson, & Raymer texts nearby :smile:. This aero stuff still amazes me! The guys who thought of calculating vortex circulation on a zero thickness camber line 2D airfoil - geniuses :smile:.
 
  • #10


kevjcarvalho said:
Thats true, but what is profile drag. Is it pressure drag, skin friction drag, or drag due to frontal area??

The two so-called sources of drag don't naturally separate, especially for airfoils. The source of profile drag is due to separation of the boundary layer from the trailing edge. On a billboard, this constitutes the entire back surface. The lost energy is found in the turbulence of the trailing wake. Frictional drag, or viscous drag, determines the boundary where adverse pressure causes the boundary layer to separate, therefore the large interdependency of the two.
 

1. What is the difference between profile drag and pressure drag?

Profile drag is caused by the frictional resistance of a body moving through a fluid. It is dependent on the shape and surface properties of the body. Pressure drag, on the other hand, is caused by the pressure difference between the front and back of a body moving through a fluid. It is dependent on the shape and angle of the body.

2. How do profile drag and pressure drag affect the overall drag of an object?

Profile drag and pressure drag both contribute to the overall drag of an object. However, the magnitude of each drag component depends on the shape and size of the object, as well as the speed and density of the fluid it is moving through.

3. Can profile drag and pressure drag be reduced?

Yes, both profile drag and pressure drag can be reduced through various means such as streamlining the shape of the object, using smooth and streamlined surfaces, and manipulating the flow of the fluid around the object through the use of aerodynamic devices.

4. How do profile drag and pressure drag affect the performance of airplanes?

Profile drag and pressure drag have a significant impact on the performance of airplanes, as they both contribute to the overall drag force acting on the aircraft. Higher drag means the aircraft will require more power to maintain the desired speed, leading to increased fuel consumption and decreased efficiency.

5. Are there any other factors that can influence profile drag and pressure drag?

Yes, there are other factors that can affect profile drag and pressure drag, such as the viscosity of the fluid, the surface roughness of the object, and the angle of attack of the object. These factors can all impact the magnitude of profile drag and pressure drag and should be taken into consideration when designing objects that need to move through a fluid with minimal resistance.

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