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pressure recovery
The wake pressure is determined by the pressure at the point of separation.
The 'wagon' style roof is undergoing slight convergence both in elevation and plan as the flow moves rearward with the air slowing and building pressure continuously until it breaks away finally at the back.The wake formed is at a higher static pressure,closer to the forward stagnation pressure so smaller delta-P,and lower drag.
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The sedans experience separation at the backlight header and C-pillars which are 'upstream' of the wagon style roof and at a lower static pressure,so the wake,necessarily must be also at a lower pressure,with a higher delta-P compared to the nose,and higher drag.
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The sedans can also experience attached vortices which typically do not form on wagon style bodies.The vorticity robs a remarkable amount of power from the engine/gas tank.
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