Hello, I have circular cylinder d=15 mm in diameter in flow velocity 5 m/s. The flow field was measured by PIV and the measured area is ca. 125x80 mm, perpendicular to the cylinder axis. The measured area extends about 8*d beyond the cylinder axis. I tried to calculate the drag according to the momentum loss it the wake, but I get values of Cd about 550. I used the formula, which calculates the drag from a drag line in the wake, which is perpendicular to the wake. (I use the formula 12.39a from Douglas, Gasiorek, Fluid Mechanics, 5th edition). Do you have any ideas, why I have so high drag coefficient value? Thanks.
I think you can check this paper.... it may help in your case to know why are getting a higher value
Article Drag Analysis from PIV Data in Speed Sports
The momentum term of drag equation could be measured by PIV. The pressure term could be reconstructed from the velocity data by solving the Poisson equation.
I did the drag calculation from the velocity PIV data according the formula Cd=(2/d)*integral((u/Uinf)*(1-u/Uinf))dy along the drag line in the wake. I know about the Poisson equation of pressure, but I dont know how to solve it.
With the knowledge of velocity field obtained from PIV, Navier-Stokes equations could be solved for pressure. There's a quite a lot of research done on this.
Article PIV-based pressure measurement
Article Principles and application of velocimetry-based planar press...
Article Non-intrusive load characterization of an airfoil using PIV
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