How Does Blasius Equation Apply to Jet Exhaust Simulations?

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Discussion Overview

The discussion revolves around the application of the Blasius equation in the context of jet exhaust simulations. Participants explore numerical methods for solving the equation, boundary conditions, and the validity of the superposition principle in this scenario.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant describes their simulation of the Blasius equation and notes that the boundary conditions differ from those of flow over a flat plate, specifically for a two-dimensional jet near the exhaust orifice.
  • Another participant mentions a particular solution to the Blasius equation, suggesting that classic superposition methods yield a specific form of the solution.
  • A different participant claims to have successfully applied the superposition principle but questions its validity for the Blasius equation, asking if it is linear.
  • One participant expresses frustration with running scripts for their simulation and requests immediate assistance with implementing the Runge-Kutta method.

Areas of Agreement / Disagreement

There is no clear consensus on the validity of the superposition principle for the Blasius equation, and participants express differing views on the boundary conditions and numerical methods. The discussion remains unresolved regarding these technical aspects.

Contextual Notes

Participants mention specific boundary conditions and numerical methods, but there are unresolved assumptions regarding the linearity of the equation and the applicability of the superposition principle. The limitations of the numerical methods and their implementation in Matlab are also noted.

Clausius2
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I have been doing a simulation of Blasius equation:

F'''+FF''/2=0 with F(eta) where eta is a similarity variable
eta=(y-1)/(x^(1/2))

F'(0)=1 u(y=1,x<<1)=1
F(0)=0 v(y=1,x<<1)=0
F'(infinite)=0 u(y=infinite, x<<1)=0

You can observe that the BC's are different of the flow over flat plate. This is obtained for a mixing thickness in the near field of a two-dimensional jet, near the orifice of exhaust (are you agree?).

in this page:
http://www.rit.edu/~pnveme/Matlab_Course/Matlab_App_ODE.html
where shooting method is employed in Matlab, it is said numerical methods (Runge Kutta, or the internal Matlab function ODE45) have normalized value F'(infinity)=1.

I have programmed it in Matlab but now I don't know how consider the value 0 at infinity instead of 1.
Could you help me?.
Thanks.
 
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particular solution

Hi, Clausius2;
It seems to me, I was wrong in my private message to you about the almightiness of SMM. The only solution that classic SMM can give us is:
F(eta)=6/(eta+C),
where C is an arbitrary constant.
See you in your old thread,
Max.
 
I have used the superposition principle:

F(0)=0 F(0)=0 F(0)=0
F'(0)=1 F'(0)=1 F'(0)=0
F'(inf)=0 F'(inf)=2 F'(inf)=2
= -


:biggrin: Hey, it seems it works!, and I did't need your help. :cool:

But now, guys, you have to tell me if superposition principle is valid for this equation. Is it linear?. Hands up if you are agree!
 
hello... I am in a real bind here. i tried runnning numerous scripts but they don't work... the programme should include runge kutta
ps: Need help pronto!
i would truly appreciate it
 

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