How can I calculate the displacement thickness of a turbulent boundary layer?

In summary, the author is trying to find a way to calculate the displacement thickness of a turbulent boundary layer. He is using a semi empirical formula that was devised by Smith and H.Gamberoni at Douglas Aircraft Company. The equation is based on a more complex method of prediction that they found. The author doesn't expect to find the exact transition point, but wants something to start with.
  • #1
Voidses_
10
0
Lets go straight to the point.

I need to find a way to calculate the displacement thickness of a turbulent boyndary layer. The laminar part has been simulated with Thwaite's method but I need to go from there. I'v heard of "Head's-model" but can't find the solution for it. Anyone that can point me in the correct direction or know of a better way?
I'll be using it in combination with a simple panelmethod-algorithm.

Thanks!
 
Physics news on Phys.org
  • #2
Well for starters, how are you determining where the boundary layer is transitioning?
 
  • #3
boneh3ad said:
Well for starters, how are you determining where the boundary layer is transitioning?

I'm planning to use a semi empirical formula that puts Rex in relation to the shape factor. I't rather long so I won't write out all of it but it looks simple enough to use.
LHS is log(Rex) and RHS depends on the shapefactor alone. When LHS=RHS transition is predicted to occur.
 
  • #4
Is this on a flat plate? I don't know what formula you are using off the top of my head but in general there is no way to find [itex]Re_{tr}[/itex]. It won't compare too well with experiments.
 
  • #5
boneh3ad said:
Is this on a flat plate? I don't know what formula you are using off the top of my head but in general there is no way to find [itex]Re_{tr}[/itex]. It won't compare too well with experiments.

I appreciate the help!
I'v realized the problems involved in predicting transition from what I'v read. And no it's not a flat plate.
This particular equation can be found in Aerodynamics for Engineering Students. The book say the method was devised by Smith and H.Gamberoni at Douglas Aircrat Co. It's based on a more complex method of prediction that they found.
I don't expect to find the exact transition point and I'm not too concerned about that at the moment either. Finding the transition point is something that can be alterd later and knowing how innacurate the rest of the algorithm is... let's just say it doesn't matter too much. I just want something to start with and work from there when the basic structure of the algorithm is working.
 
  • #6
Well at any rate, I can't really help you off the top of my head until I go back to work Monday. There are two sources that jump to mind that may have the information in there, which are "Boundary-Layer Theory" by Schlichting and "Turbulent Flows" by Pope. You may want to check there. I just don't remember off the top of my head because my work doesn't deal with turbulence and my copies of those books are at work.
 
  • #7
Great, Thank you!
I'll check with the campus library if they have them.
 

1. What is a turbulent boundary layer?

A turbulent boundary layer is a layer of fluid that is in direct contact with a solid surface, experiencing a significant amount of fluctuation and mixing due to turbulent flow. It is characterized by chaotic and unpredictable motion, as opposed to a laminar boundary layer which is smooth and orderly.

2. How is a turbulent boundary layer formed?

A turbulent boundary layer is formed when a fluid flow encounters a solid surface and is subjected to disturbances such as changes in surface roughness, pressure gradients, or flow velocity. These disturbances cause the flow to transition from a laminar to a turbulent state, resulting in a turbulent boundary layer.

3. What are the effects of a turbulent boundary layer?

A turbulent boundary layer can have both positive and negative effects. On one hand, it can enhance heat and mass transfer, which is beneficial in certain applications such as mixing and heat exchangers. On the other hand, it can also increase drag and energy losses, which can be detrimental in situations such as flow over an aircraft wing.

4. How is a turbulent boundary layer measured and studied?

There are various techniques used to measure and study turbulent boundary layers, including hot-wire anemometry, laser Doppler velocimetry, and particle image velocimetry. These methods allow scientists to gather data on flow characteristics, such as velocity and turbulence intensity, which can then be analyzed to better understand the behavior of turbulent boundary layers.

5. Can turbulent boundary layers be controlled or manipulated?

Yes, turbulent boundary layers can be controlled and manipulated to some extent. For example, by introducing small disturbances or altering the surface roughness, the transition from a laminar to a turbulent boundary layer can be delayed or advanced. However, complete control over turbulent boundary layers is still a challenge and an active area of research in fluid dynamics.

Similar threads

  • Aerospace Engineering
Replies
7
Views
1K
  • Mechanical Engineering
Replies
7
Views
7K
  • Aerospace Engineering
Replies
2
Views
10K
  • Materials and Chemical Engineering
Replies
1
Views
2K
  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
1K
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
8
Views
2K
Back
Top