Drag force is any undesirable effect occurring when a body is moving through a fluid. It is generated by the interaction and contact of the body with the fluid (liquid or gas). There are different forms of drag depending on your case study.
what kind of geometry are we talking about? drag depends on the shape of your object. What kind of drag are we talking about here... in general drag is calculated in aerodynamics using the following formula.
D = Cd * 0.5 * Span * dynamic pressure
Its different for different objects though... rephrase your question properly please.
sir, i want to know about the drag force of paddy. my project is to design a pneumatic paddy collector.
No need to use sir.. :)
Well usually out of experiments, everyone arrives at an analytical formula for finding out drag which usually has a decent accuracy. In your case, i would suggest you to develop a 3d numerical model and run a cfd simulation for 3 different cases. Usually drag prediction is one of the difficult thing in computational fluid dynamics. Yet in your case, a small amount of error wouldn't be too much. So run simulations and see if there is a large difference between 3 cases... and use the constant Cd value that you would get from the simulation.
Either way, i would suggest you to find some literature in which this has been probably done... :)
Thank you for your reply.. i tried many but couldn't find any literature related to this yet.
drag force would be given by integral of shear stress over the effective
surface of the body.
Shear stress can be evaluated from viscosity of the substance multiplied by
strain rate. Strain rate is linked to the velocity of the body . it will
be roughly proportional to the ratio of the velocity to the length or width (depending
on the orientation) of the body. In more sophisticated way it can be computed by
tracing displacements of reflective micro-particles ( added to the fluid ) in the boundary layer surrounding the body
There are 2 different components to drag. One is the skin friction drag - mentioned by others above, and then there is normal pressure drage. At very low Reynolds numbers
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