You can compute the drag coefficient using the drag force equation. To do so, perform the following steps:
Take the fluid density where the object is moving.
Multiply it by the reference cross-sectional area and by the square of the relative velocity of your object.
Find the value of the drag force over your object and multiply it by 2.
Divide the last by the result of step 2 to get your drag coefficient as a non-dimensional quantity.
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