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 Lee,jangho August 29, 2000 01:39

boundary layer thickness

hi? i am graduate student in south Korea. i HAVE useD luent5.1 and solved NACA 00XX SERIES i want to mesured the boundary layer thickness at the trailing edge of airfoil. but i can find any display item about that. anyone who know any means write the answer to me thanks...

 John C. Chien August 29, 2000 03:52

Re: boundary layer thickness

(1). I guess, you need to define the boundary layer thickness in the first place. (2). Once you have define that, you can use the computed results to derive the boundary layer thickness.

 Kai Kang August 29, 2000 13:56

Re: boundary layer thickness

You can use the definition of bc layer thickness to define a scalar (under \DEFINE in Fluent) to represent the boundary layer's boundary. If that's not work, you might need to do a little own post-processing instead of clicking on Display...

 Lee,jangho September 24, 2000 22:06

Re: boundary layer thickness

thank for replaying to everyone. but i can't understand actually if you have more time , please write more detail. thanks...

 John C. Chien September 25, 2000 00:09

Re: boundary layer thickness

(1). At the location where you want to compute the boundary layer thickness, say just befor the trailing edge, you can display the velocity profile from the wall to the outer boundary . (2). For the flow over the airfoil, you should have two boundary layers, one on the top (the suction side), and the other on the bottom (the pressure side). (3). If you define the edge of the boundary layer as the location where the velocity is 99.5% of the local free stream velocity value, then you can calculate the location of the edge of the boundary layer.(measured from the wall) So, at the trailing edge location (a straight line) you need to define the local free stream velocity.(this is when the velocity is uniform. It may not be easy if the flow is somewhat non-uniform, but, the boundary layer concept is derived based on the uniform local free stream concept.) (4). Whether it should be 99.5% or 99.9% , it is up to you, as long as it is used consistently. (5). So, draw the velocity profile along the trailing edge location from the wall to the free stream or outer boundary. Draw a parallel line to the local free stream velocity at the 99.5% value. The location where the profile value is 99.5% of the local free stream velocity is the edge of the boundary layer. The boundary layer thickness is : the thickness measured from the (trailing edge) wall to the edge of the boundary layer. (6). By the way, if you don't have enough number of mesh points inside the boundary, it is going to be difficult to find the location of the edge of the boundary layer accurately.

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