View Single Post
Old 05-29-2020, 08:38 AM   #2 (permalink)
Cyborg ECU
California98Civic's Avatar
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,297

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
Thanks: 2,373
Thanked 2,155 Times in 1,463 Posts
The tufts and the pressure readings visualize what is happening on the surface of the car. Add a third visualization. Wind tunnel smoke trails can help tell the story of what is happening in the area above the tufts.

Wind tunnel smoke trail pics are usually taken for promotion and they love to maneuver the wand to create bowing arches of gentle beauty. But the EM thread of wind tunnel and smoke trails has some shots that tell a messier story of the roof.

On this somewhat older Mercedes red dramatically highlights the vortices beginning to grow at the windshield header.

On this Caddy (more like your jag), the trail in the flow also begins to show vortices and breakup just behind the windshield header. It is less dramatic but you can see the growing disturbance of the smoke begin just behind the windshield header.

In this light, your pressure readings confirm the possibility that vortices are beginning to develop across your jag's roof just behind the windshield header. Your pressure readings show that pressure begins to return before reaching the point of greatest roof camber (from -105 to -95 ) and continues to climb after (‐50, -10, +30). That story of rising pressure in the flow is associated with the story of growing vorticity seen in the smoke trails.

And all the while the tufts would be pasted flat even across parts of the very messy rear window and trunk. Take for example my tufts from my Civic. They look smoother than expected after 45 mph 7 years ago when I took this shot. The vortices off the c pillars and the downwash from the roof are doubtlessly more turbulent than on the sides or the roof but the tufts can barely tell that story.

See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

Last edited by California98Civic; 05-29-2020 at 08:45 AM..
  Reply With Quote
The Following User Says Thank You to California98Civic For This Useful Post:
aerohead (06-03-2020)