Profile Drag and Pressure Drag???


by kevjcarvalho
Tags: drag, pressure, profile
kevjcarvalho
kevjcarvalho is offline
#1
Jun7-10, 09:18 AM
P: 42
Can someone please tell me the difference between profile drag and pressure drag if there is one??.
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Cyrus
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#2
Jun7-10, 09:32 AM
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Try Google, this is very basic. If you don't get stuck there, repost here and I'll help you.
kevjcarvalho
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#3
Jun7-10, 09:53 AM
P: 42
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, shouldnt 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.

dtango
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#4
Jun7-10, 11:12 AM
P: 43

Profile Drag and Pressure Drag???


Quote Quote by kevjcarvalho View Post
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, shouldnt 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.
abhi88
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#5
Jun7-10, 11:46 AM
P: 3
Quote Quote by kevjcarvalho View Post
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, shouldnt 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 wont have any effect on lift (atleast not much significant effect).
kevjcarvalho
kevjcarvalho is offline
#6
Jun7-10, 01:08 PM
P: 42
Thats true, but what is profile drag. Is it pressure drag, skin friction drag, or drag due to frontal area??
dtango
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#7
Jun7-10, 01:27 PM
P: 43
Quote Quote by kevjcarvalho View Post
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.
Cyrus
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#8
Jun7-10, 01:33 PM
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P: 4,780
Quote Quote by dtango View Post
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.
dtango
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#9
Jun7-10, 01:49 PM
P: 43
Quote Quote by Cyrus View Post
Great post.
Haha thanks. I happened to have my Phillips, Anderson, & Raymer texts nearby . This aero stuff still amazes me! The guys who thought of calculating vortex circulation on a zero thickness camber line 2D airfoil - geniuses .
Phrak
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#10
Jun13-10, 03:55 AM
P: 4,513
Quote Quote by kevjcarvalho View Post
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.


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