Has anyone tried one or more spherical chambers in a riser to create low pressure zones?

I was wondering if anyone has ever experimented with something like a basket ball size sphere inline about half way up a 6 inch riser configuration, then closing back down to the 6 inch riser diameter for the rest of the riser.

or possibly more than one sphere in a line in the riser.

Or possible different shape like a toroid.

I was wondering if this would create a low pressure zone(s) that would cause the unburned gasses to slow down and mix around in the chamber, and also a super heated flame would be shooting right into the slower gasses possibily helping to combust them?

I understand this is essentially the effect the top of the barrel has. I was just curious if closing the diameter back down again, with a ratio of dimensions that would still keep the airstream moving through the riser would have any kind of interesting effect.

Anyone have any thoughts on this?

Scramjet