# Need Help With FLUENT.

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 January 17, 2013, 12:40 Need Help With FLUENT. #1 New Member   Sárán Greene Join Date: Nov 2012 Location: Dublin Posts: 13 Rep Power: 6 Sponsored Links I'm currently in my final year of studying Mechanical Engineering. My final year project is to analyse lift and drag over a 2D hydrofoil. I've followed various tutorials regarding Airfoils and have produced results that correspond to those in the tutorials. I've been using the SA model for most of my models. The project itself isn't concerned with compressible flow or cavitation. The problem I'm having at the moment is my Cd oscillates violently for the first 20 or so iterations, then settles down for the next 100 or so iterations and then begins to oscillate violently once more. In boundary conditions for my inlet, or farfield, I chose components under velocity specification method. For the x-direction I used the formula Vcos(theta), where V is the initial velocity and theta is the AoA. I set up a Lift and Drag monitor also. For the Drag monitor I used cos(theta) for the force vector of X and sin(theta) for Y. Any insight into where I might be going wrong would be greatly appreciated. Thanks in advance, Saran.

 January 17, 2013, 14:01 #2 Senior Member   Join Date: Mar 2011 Location: Germany Posts: 431 Rep Power: 13 Cd can't converge in 120 iterations as you are expecting, it will take many more iterations. So let the solver run for more iterations.You are wrong in setting the components for force, set sin(theta) for x-force vector and cos(theta) for y-force vector BTW at what AOA you are performing the analysis? Saran1991 likes this.

 January 17, 2013, 14:49 #3 New Member   Sárán Greene Join Date: Nov 2012 Location: Dublin Posts: 13 Rep Power: 6 Thanks for the reply. I'm conducting multiple AoA. 0, 4, 8 and 12 degrees. I had my simulations running for 250 iterations but it just kept oscillating and then steadying out over and over again. Thank you again.

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