I noticed on your graphs that there wasn't a "kammback off/tail on" scenario. I know that seems counter-intuitive but it would have been an interesting approach. Perhaps even just for the curiosity of it.
I think the results are due to the notchback design on the civic. Perhaps Honda did a really great job at the rear of the car, meaning a rather "clean" separation after the decklid. I know it is too late now, but I wonder if removing the kammback and leaving the tail might have netted better results. It might have unlocked an untapped synergy.
The kammback certainly improved the flow on top, but it might have been interfering with the c-pillar vortices, causing the net efficiency gain to be somewhat lower than expected. Pressure differentials on the boattail surface might also be the culprit. I believe we want an
even pressure recovery.
Given that the rear glass angle and overall design was already optimized by Honda, adding the tail only might have netted better efficiency gains, as it would help the pressure recovery aft of the decklid, where the airflow does usually re-attach in notchback designs.
Food for thought I guess. Thanks again for the hard work; it never ceases to amaze me.
