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-   -   Blasius equation help :( (https://www.cfd-online.com/Forums/main/86299-blasius-equation-help.html)

johnt447 March 18, 2011 18:57

Blasius equation help :(
 
Hello so I'm working on the blasius solution for incompressible viscous flow. So far I have solved for f' and successfully plotted a graph of flow speed against http://www.physicsforums.com/latex_i.../3195850-0.png. So from what I understand this is correct I got a gradient of velocity from 0 to the flow speed. Now i want to extend it to different values of x. Now this is my issue, the book I have has a equation for du/dy so my plan was find the gradient for each different value of x, hence since i know it always starts at 0 and ends at the flow speed i could find the points in between. Although when trying the equation out I found my gradient was in fact decreasing as x increases. As far as I understood the gradient (du/dy) should become larger as x increases. The equation I'm using is this
http://www.physicsforums.com/latex_i.../3195850-1.png

where http://www.physicsforums.com/latex_i.../3195850-2.png is flow speed, http://www.physicsforums.com/latex_i.../3195850-3.png is kinematic viscosity, u is speed and why y and x are the coordinates.

So what I did was use the equation with f''(0) bit included I wasn't sure if that has to change I thought since the gradient in a incompressible flow is constant.

Also there is something I'm not sure about, I have set the y velocity to 0. so i just have vectors going horizontal. I wasn't sure if that is right or not looking from the diagram in a textbook i have seemed right but I'm not sure :(.


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