# Skin Friction Lines - Some Comparisons

Discussion in 'Hydrodynamics and Aerodynamics' started by Leo Lazauskas, Feb 15, 2013.

1. Joined: Aug 2004
Posts: 3,879
Likes: 1,245, Points: 113, Legacy Rep: 2040
Location: Port Orchard, Washington, USA

### jehardimanSenior Member

Sorry I'm getting into this late,but before we get too carried away, lets put some perspective up.

A swimmer is Rn 1x10^6
A 3m row boat is Rn 7x10^6
A 10m sail boat is Rn 3x10^7
A 10m power boat is Rn 9x10^7
A 100m ship is Rn 6x10^8
A CVN is Rn 3x10^9

As far a Naval Architecture is concerned anything below 1x10^7 is not of interest and realisticly for commericial applications anything below 1x10^8 is a "just throw power at it" problem. Throw in wave orbitals which cause an order of magnitude change over the length of a ship and the fact that there is no laminar flow on rigid bodies in open water above 1x10^6 and you can see that this will devolve quickly into bottle washing and button sorting.

2. Joined: Jan 2011
Posts: 317
Likes: 58, Points: 28, Legacy Rep: 172
Location: Germany

### Remmlingerengineer

Just take a yacht with a length of 10m, which has a fin keel with a chord length of 0.8m. The yacht is sailing at 4 Knots. Now you want to test this case in a towing tank with a model of 2m length. You measure the total force and you want to subtract the viscous resistance of the keel to get the resistance of the canoe body. How would you calculate the viscous resistance of the keel? The chord based Reynolds number for the model is in this case 1.4 * 10^5

3. Joined: Jan 2002
Posts: 2,696
Likes: 155, Points: 63, Legacy Rep: 2229

### Leo LazauskasSenior Member

Thanks, I guess, for bringing reality into it.

But for some us non-NA's there are many applications where it
does matter. I have interests in under-water turbines, struts, fins
and keels, and UUV, and almost no interest in laminar flow.

On a slightly related note, have you come across any measurements of
the kinematic eddy viscosity of water in the open sea? From what I
can gather it can vary by up to 6 orders of magnitude.

Yeah well you know? That's just like your opinion man.
I thought a NA's primary function was to provide adequate free-board.

4. Joined: Jan 2011
Posts: 317
Likes: 58, Points: 28, Legacy Rep: 172
Location: Germany

### Remmlingerengineer

5. Joined: Jan 2002
Posts: 2,696
Likes: 155, Points: 63, Legacy Rep: 2229

### Leo LazauskasSenior Member

Thanks, Uli.
I knew of it but I didn't have it. It seems to be an earlier version of some
papers that I (and you) already have by those three authors. I think some
of the work on the wake parameter (Uppercase Pi) have been reconsidered
in the later works.

If you are collecting papers, I would also look at some more recent work by
Ramis Orlu. His thesis discusses much of the same stuff and includes some more experiments.
http://www.mech.kth.se/mech/info_staff.jsp?ID=198

6. Joined: Aug 2004
Posts: 3,879
Likes: 1,245, Points: 113, Legacy Rep: 2040
Location: Port Orchard, Washington, USA

### jehardimanSenior Member

I know that there was some ADCP and LDVL data taken in the littorials in the last few years. I bet if you were to go ask for some raw REMUS ADCP data you would see it. Processed data won't work but the raw feed (like for Teledyne RDI waves array) will.

Nope, it is to give the captian a good place to stand and be seen when sailing into port.

#### Attached Files:

• ###### Anton_Romako_001.jpg
File size:
340.3 KB
Views:
403
7. Joined: Jan 2002
Posts: 2,696
Likes: 155, Points: 63, Legacy Rep: 2229

### Leo LazauskasSenior Member

Perfect, jeh. "REMUS" was the key to narrowing down the search.

8. Joined: May 2006
Posts: 574
Likes: 83, Points: 28, Legacy Rep: 258
Location: Finland

### Mikko BrummerSenior Member

I have been thinking so but can you give some evidence for the claim?

9. Joined: Oct 2012
Posts: 36
Likes: 3, Points: 0, Legacy Rep: 25
Location: berlin

### hariboJunior Member

IMO this "fakt" is only correct for stady flow over straight surfaces

not necessarily for flow with acceleration (speedup) thus unstady flow and
not necessarily for also rigid but curved bodies

centrifugal forces may hold the waterparts longer in a laminar pathway....

1 person likes this.
10. Joined: Jan 2002
Posts: 2,696
Likes: 155, Points: 63, Legacy Rep: 2229

### Leo LazauskasSenior Member

And slight oscillations in surge, yaw and pitch, as well as ambient waves (small
chop or large swell) and turbulence could prevent that flow from staying laminar.
It is a very complicated matter!

11. Joined: Oct 2012
Posts: 36
Likes: 3, Points: 0, Legacy Rep: 25
Location: berlin

### hariboJunior Member

and the fast not rigid-body swimmer in the water are quite clever in uses their benefits in this case

12. Joined: May 2006
Posts: 574
Likes: 83, Points: 28, Legacy Rep: 258
Location: Finland

### Mikko BrummerSenior Member

Does somebody know what would be a typical turbulence intensity in the sea surface layer?

13. Joined: Jan 2002
Posts: 2,696
Likes: 155, Points: 63, Legacy Rep: 2229

### Leo LazauskasSenior Member

Follow jehardiman's suggestion in an earlier post and search for REMUS etc.
There are some papers and graphs that show how it varies with depth, salinity,
upwelling, proximity to shore etc etc.

Last edited: Feb 21, 2013
14. Joined: May 2006
Posts: 574
Likes: 83, Points: 28, Legacy Rep: 258
Location: Finland

### Mikko BrummerSenior Member

You would look up the corresponding cdp of your keel profile, at the given Re and given CL. I seem to use in my VPP

Cdp =15/(KeelRe)^0,2*(0,008+0,017*(RootChord+TipChord)/2+0,0042*CL^2)

(don't ask where it comes from)

15. Joined: May 2006
Posts: 574
Likes: 83, Points: 28, Legacy Rep: 258
Location: Finland

### Mikko BrummerSenior Member

Thanks.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.