See also High drag coefficient - #43 by PierreB. I reproduce the link of the publication: A Numerical and Experimental Study ofthe Aerodynamics and Stability of a Horizontal Parachute, where the figure 3 shows a similarly shaped curve but with more different values of Cd, and where “the drag coefficients are calculated numerically” (Abstract).
I mention also two very interesting observations from Dave Santos:
Pierre continues exploring interesting aerodynamic complexities of kite-like objects, citing the paper linked below, which in turn cites prior work along similar lines.
Here the higher relative velocity (higher Re estimation) lower Cd anomaly has yet another obscure cause, this time mostly inherent to drogue canopies with shroud lines. Many of these sorts of experiments and their simulations only explore narrow bands in tunable parameters. Narrow dynamical observations may show local linearity in overall nonlinearity, or complex reversals of general dynamics.
As velocity increases from zero, a drogue inflates, Cd at first rises roughly according to increased projected area. However, as velocity continues to rise, new dynamics present. Projected frontal area can decrease by “jellyfish” variation. Enhanced laminar bypass flow by the billowing gores can reduce Cd somewhat as a golf ball with dimples flies farther. Elasticity in shrouds and their rigging trigonometry figure strongly in observed dynamics. Re is a slippery parameter, for example, effective reduction in frontal area factors Re lower. And so on.
This student ME work did not dig too deep in an AE subject (aerodynamics), a lesson in caution for kite pros.
In general, Bluff-Body Cd is a function of frontal area, but one must control carefully for higher-order complexity, to not be puzzled or misled.
The second Dave’s observation (below) concerns the possibility of exploiting and even causing instability as a means of power take off (PTO). I had experimented a little with a parachute oscillating due to instability, and capable of exerting a (limited) action on winch-generators (here dog leashes) alternating.
A whole further subject is drogue oscillation dynamics (treated in the paper by Strouhal Number) which can be passively tapped as free-energy for AWE, which kPower over a decade at subscale mastered in praxis, but active control AWES developers disregard. All aircraft are complex oscillators. Kite Oscillations are normally damped by design but can just as well be amplified by design, within stable limit cycles.