Documenting NHW11 Prius rear window flow separation; testing AirTab vortex generators
 

What speed are the photos taken at? 50km/hr like in the article? Are you going to use some AirTabs and see if there is an improvement? Interesting article... Perhaps worth trying something under the front end to see if there is improved stability with no hit to FE, or maybe a slight boost.

Has anybody done any testing with these on a notchback to see the effect?

Bob's Prius is the earlier model that is a notchback.

The next thing I'd be wondering is: does the flow reattach on the end of the deck lid?

Did all the 1st gen Priuses come with rear spoilers? A quick Google image search suggests they did.

No, the FIRST (NHW10) Prius did not have a rear spoiler.

Over in "Prius Technical Stuff" there was a posting that removal of the rear spoiler from the NHW11 (2001-03) model reduces mileage. Furthermore, there is a slot that runs across the bottom with what feels like a 1 cm, rectangular shape. I suspect this slot generates a linear vortex to improve the efficiency of the rear 'wing.'

It is a good question: does the flow reattach? I need to tuff the top of the trunk to see what is happening.

Right now, it looks like a dozen of the Airtabs would keep the flow attached to the rear window. The question is whether or not it might cause something else to 'squish out.' Still it might allow removal of that rear spoiler without an increase in drag.

Most rear spoilers are there to increase down-force for road racing. Somehow, I don't think there has been much discussion about drag reduction.

Bob Wilson

My opinion, based on as-controlled-as-possible A-B-A testing (straight & level road, absent any other traffic, cruise controlled, back to back bi-directional runs) is you'll not likely see any drag reduction using AirTabs. Seen this? http://ecomodder.com/forum/showthrea...olla-2390.html

It's fairly well known that some rear spoilers reduce drag (and rear lift).

They are typically added to most sedan/notchback hybrids (and other high efficiency versions of that body style), where the "regular" edition may have none.

Honda Canada added a small deck lid spoiler to its non-hybrid sedan/coupe as one of a series of measures meant to marginally reduce the car's fuel consumption to make it eligible for federal incentives.

Car and Driver measured drag reduction on both its "Crisis Fighter" ecomodding project cars years ago (See the Pinto project here). Their Datsun 240 project also benefitted (through reduced fuel consumption) from a spoiler addition.

Thanks! A few questions:

1. How much warm-up time and speed before the first "A" test? (Prius warm-up is ~30 min., thermal changes takes about 5-10 minutes.)
2. How much warm-up time before the first "B" test?
3. How much warm-up time before the second "A" test?
4. How many minutes per run?
5. Ambient temperature that day?
6. Start and stop times?

My hypothesis is driving to the test area may have been long enough to warm-up the vehicle. Entering the first "A" protocol would have 'good data.' Then adding the vortex generators would allow the vehicle to 'cool off' somewhat. Then taking off the vortex generators for the second "A" appears to be much closer to the "B". I think I'm seeing the pattern in a plot of the data.

What has peaked my interest in the protocol is the second "A", especially the "West" runs really look different. The "East" runs are more consistent ... given the limited number of runs.

Are the vortex generators still available?

I am thinking about replicating the test using 104 kph (65 mph) that corresponds to the last plateau before MPG drops off.

Thanks,
Bob Wilson

The day of the test, the max temp was 18C - I didn't record the actual early evening temp when I ran the test. It takes me 20-25 minutes to get to the test route (combination of sub/urban and rural driving). The car may also have already been warm prior to setting out (didn't make a note of that).

The airtabs were attached with tape in approximately 2 minutes. The engine was left on during this.

It would have taken less than a minute to remove the tabs, engine left running again.

1.6 km at 90 km/h for the run itself (~64 sec), plus time getting up to speed, plus time coasting to a stop, jotting down the run data & turning the car around. 2-3 minutes per run is probably a good guess.

Yes. I can send them to you if you like. PM me your mailing address.