# Drag Coeffecient Calculation

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 April 3, 2005, 02:52 Drag Coeffecient Calculation #1 Mohamed Sobh Guest   Posts: n/a 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?

 April 4, 2005, 14:26 Re: Drag Coeffecient Calculation #2 Jarmo Monttinen Guest   Posts: n/a 1. Include viscous drag in your calculation 2. Cd will change with Re which in changing when you change the dimensions. -- Jarmo

 April 4, 2005, 15:33 Re: Drag Coeffecient Calculation #3 Mohamed Sobh Guest   Posts: n/a 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?

 April 5, 2005, 13:10 Re: Drag Coeffecient Calculation #4 Jarmo Monttinen Guest   Posts: n/a Pressure drag - pressure * area Viscous - viscosity * du/dn * area Or something along those lines. Any fluids book should have this. -- Jarmo

 April 7, 2005, 21:15 Re: Drag Coeffecient Calculation #5 Shrinivas Guest   Posts: n/a 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

 April 8, 2005, 15:07 Re: Drag Coeffecient Calculation #6 Mohamed Sobh Guest   Posts: n/a 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