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Drag Coeffecient Calculation

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Old   April 3, 2005, 00:52
Default Drag Coeffecient Calculation
  #1
Mohamed Sobh
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I solve structured grid volume arround sphere using navier stocks equations , it exact the same flow paths like those produced from fluent, when i calculate the drag coeffecient, it always gives different values for different sphere diminsion, i use pressure*area integration arround all ponits of sphere border to get the drag force, but i always get wrong value of Cd (1.3-->4.9), any one can tell me the reason and how to detect the problem in my code?
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Old   April 4, 2005, 13:26
Default Re: Drag Coeffecient Calculation
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Jarmo Monttinen
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1. Include viscous drag in your calculation

2. Cd will change with Re which in changing when you change the dimensions.

-- Jarmo
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Old   April 4, 2005, 14:33
Default Re: Drag Coeffecient Calculation
  #3
Mohamed Sobh
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Can you please give me a valid fromula to calulate the prssure and viscuse terms in the drag force. i want to be sure of my equations?
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Old   April 5, 2005, 12:10
Default Re: Drag Coeffecient Calculation
  #4
Jarmo Monttinen
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Pressure drag - pressure * area Viscous - viscosity * du/dn * area

Or something along those lines. Any fluids book should have this.

-- Jarmo
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Old   April 7, 2005, 20:15
Default Re: Drag Coeffecient Calculation
  #5
Shrinivas
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hi ! Even i am writing a code for Cd but it is around a cylinder. Please help me in grid discritization as i am mesing up th grid thts why i got errors. Please give me links or method of grid u used so tht I can have an idea for a cylinder

Thanks ANy help will be appreciated
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Old   April 8, 2005, 14:07
Default Re: Drag Coeffecient Calculation
  #6
Mohamed Sobh
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actually i use a structured gride "cubes" arround the sphere, it is more simple for calculation, put untill now i fail to get an accurate value for Cd
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