Starting to think 2010 Prius has flow separation issues. Comments?

[donee]

Hi All,

Welp, I took the car to the dealarship, and had the alignment check. Since it was dead on perfect as one would expect, I paid the $130 for the check. The local independant shop I favor for alignments could not do the work as their software did not have the 2010 Prius update.

So, this coasting problem is not the toe-in being outboard. The front spec is 0 to .20 degrees inboard, and my car varied but was never out of this spec with manipulation of the front end. Apparently, Toyota has tightend up on this spec from the Gen II. The left rear was near specification nominal (spec -.01 to +.29). The right rear was a little towards the outboard spec limit (-.01 degrees) but still inboard (.04, and .07 in the two measurements).

So, this is getting interesting now.

I saw some side-by-side pictures of the Gen II next to the Gen III. The Gen III is a much wider/lower design, where the Gen II has a much more square aspect cross-section. This may mean the flow delamination may not be over the top, but around the sides. As the air has further to go to get back into the undisturbed flow around the sides.

If I can proove that, then one fix would be vertical plates at the rear of the car, set just inboard of the lights.



Take a look at the Aerocivic, and its a quite square cross-section car too.

[donee]

Originally Posted by bwilson4web

Sorry but I haven't measured the coast down characteristics of either car, yet. However, both have Sumitomo T4s and six of eight tires are 195 width and the other two 175s.

My posting was to suggests some areas that may impact rolling resistance. All I've done for aerodynamics testing with the ZVW30 has been some lower inlet testing in cold weather.

Bob Wilson

Hi Bob,

Your comments are welcome.

Yea, I read about you using the small tires on the back of your Gen I Prius.

I have put on grill dams (vertical plates to isolate flow into the grill only across the opening in the grill).

I am doing about 60 mpg actual on this car, 4th tank, about 2000 miles. I am not too concerned about this being 8 mpg lower than I would be getting in my Gen II.

I am concerned about the poor coast down performance. If it can be brought back up the Gen II standard, I might have 70 plus tanks in a year with the warm weather and a broken in drive-train. The Gen III Prius has allot of fixes in its warm-up cycle. Like not recycling down to the lower warm-up stages if the car should cool off (as when the thermostat opens on hot days). In the Gen II this results in the car not going into a engine shut-off during a coast. The Gen III does not do this. And also will go into engine shut-off as low as 25 mph when in the Stage 3 of the warm-up cycle (versus 35). Which is very useful...

So, its kinda a shame with all the improvement they have made, to have it not have a mileage improvement impact because of the aero-dyanmic (now) styling, rather than engineering it was with the Gen II car.....

Or at least that is my concern...

[donee]

Hi All,

I am believing more than ever that the 3rd Gen Prius is backwards aerodyamically. If you put a 2nd Gen next to a 3rd Gen you will maximum height of the 2nd Gen is much further forward.

I had some magnetic sign material laying around. I cut some triangular notches in the front and back, 180 degrees out of phase, so the material pointing forward is followed by a gap pointing forwared. Aka ZIG-ZAG pattern. But, as the magenetic material needs some surface area to stay stuck, the distance between the 1 inch deep 45 degree notches front-to-back is about 3 inches. The width of this is 18 inches.

I placed it across the central portion of the roof, about 6 inches back from the windshield. The intent of this, was to try and see how this works, them move it further back until a traditional turbulator position was obtained (just behind the maximum thickness / height of the shape). I had a trip yesterday to see relatives, and it seemed to be working OK. The car would change speed in the SHM peddle positions readily, on level road, which it would not do previously. This was with a slight head wind. Normally, one would have to abandon SHM completely to get the 3rd Gen Prius to accellerate a mph or more in any time under 10 seconds. That was not the case yesterday. But, this is somewhat subjective too. And not being familiar with the route, it was hard to say if there was any change.

Welp, today I am on the commuting route. And there is one hill I have talked about where the 2nd Gen would accellerate down in warp stealth, and the 3rd gen would loose speed. Today, my 3rd Gen gained at least 1 mph down this hill. That is a reversal of at least 3 mph, from previous performance. Wind was out the broadside direction, the road was wet, and it was raining. So, hmm, so far so good!



The

[bwilson4web]

Sounds like it is time for some tuft testing. I'll see what I can do next weekend.

I'm assuming you are concerned about the roof air flow and nothing on the side?

Bob Wilson

[donee]

Hi Bob, and any others watching,

Not good news regarding my mod this week. That first roll down must have been a fluke. I have see 1 to 2 mph dropps in speed down the hill during the driving this week. The only one good day (dry road, trailing wind, but cold - 35 F) I had a 2 mph drop in speed.

So, there might be some improvement, but little if any.

I also got a veiw of water droplets behind the turbulator. When the droplets are big, the patern behind the turbulator is little different that in front of it. When the droplets were a fine mist, there was some change in the droplet pattern, turning into what looks like a flowing stream pattern.

So, the turbulator is not turbulating very well. I could double the number of spikes on it. Right now there are 13 spikes across 19.5 inches, and the spikes are 1 inch deep, and the total turbulator length (in the direction of flow is about 4.5 inches. Which makes a 2.5 inch flat section between the leading and following spikes.

Or, I could go to a zig-zag tape style pattern, and hope the magnetic material holds. , where the zig-zag length in the direction of flow is equal to the depth of the spikes. So, that would be 1 inch deep spikes, with 1 inch from the tip of one spike, to the rear inset tip.

Or both (double the spikes - spike depth 1/2 inch), with 1/2 inch wide tape.

[donee]

Hi Bob,

Are you all right down there? Did the tornados come by your area ?

[XJguy]

Originally Posted by donee

Yea,

The 2006 has a Cd of .26, with a 5.83 CdA, while the 2010 has a Cd of .25 with a CdA of 5.84. Those CdAs are very approximate, using just height and width , and not a shaddow area. The 2010 has significantly larger mirrors, and wider tires (195s versus 185's).

But the new Prius has nice and sharp trailing edges whereas the former has rounded (bad).

[donee]

Hi XJ,

I think the problem is where the maximum chord is. In the 2nd Gen Prius the maximum chord was over the forward part of the front seat location. But in the 3rd Gen Prius is over the rear seat. This results in either a steeper angle from the maximun chord to the rear of the car (over the top of the car), or a higher rear spoiler position.

So, the air flyies up the forward ramp surfaces, and gets shot off, creating a delamination bubble. And the steeper rear angle, or higher rear spoiler does nothing to keep the air attached, and probably exacerbates the delamination.

While the 3rd Gen Prius have better side rear transistions, it also has a much bumpier side construction. The 2nd Gen Prius was perfectly smooth along the sides of the car. The 3rd Gen has all this malarky muscle car tire bulge bs. Which can only create drag. There is not allot I can do about that.

I began looking for A-pilar problems, as I hear tremendous turbulence there with side winds, in comparison to the 2nd Gen Prius. But putting tubulators there apparently made things worse, based on salt patterns. They may have traded off in-line Cd for cross wind Cd with the design changes to the windshield inset in that area.

Besides the tires being larger, the wheel well openings are huge in comparison to the tire size, on the Gen 3 compared to the Gen 2. Just plain silly - the car is designed to be lowered, rather than properly design for the tire sizes in the first place. Since its impractical to lower the Prius here with all the pot-holes, its just a pain the way the car is now.

[MetroMPG]

Originally Posted by donee

So, the air flyies up the forward ramp surfaces, and gets shot off, creating a delamination bubble.

This is highly, highly unlikely.

Before you spend more time with zig zags and turbulators on the leading edge of your roof, you owe it to yourself (and to other readers of this thread -- members and non-members alike) to _demonstrate_ that the underlying "problem" you're trying to correct actually exists in the first place.

Otherwise we're generating lots of heat, and no light in this thread. Creating unnecessary turbulence, even.

I believe that tuft testing will show the airflow is doing nothing unusual at the windshield/roof transition.

[donee]

Hi Metro,

Take a look at the side-profile of a 3 rd Gen Prius, versus the streamlining template, and a 2nd Gen. The 3rd Gen looks like a 2nd Gen backwards. The 3rd Gen looks like the streamlining template backwards in side profile.

The Prius is not like other cars. Above the radiator level the surfaces are not blunt, but sloped. In other cars, these surfaces are horizontal up to the windshield. The 3rd Gen takes this even further, where the front slope is longer than the rear slope, not reaching a peak till behind the front seat. Remember, I have one of these out on my driveway.

And I used to have a 2nd Gen out on my driveway. Which was rather blunt up front, except for the windshield. And it had a long slope from above the drivers head down to the rear spoiler.

I started asking myself these questions when I was trying to figure out how they got all the under-hood space in the 3rd Gen. The 2nd Gen is really packed in there, the 3rd Gen, even with the bigger engine has lots and lots of space under the hood. Where did all that room come from? From the long front taper the 3rd Gen has.

Having a long slope , the air does not shear away over the top like the streamlining template would cause.

I guess you gotta ask yourself if you take a boatail car and run it backwards, if it would have less drag. Because that is what the 3rd Gen Prius is.

As far as further testing goes, well, the weather and other considerations are not permitting me at this time. Water patterns are commonly used to check aerodynamic device effects, and I have commented on those for the initial device.

I am running a .035" thick tubulator behind the peak height right now. It seems to give a 1 mph advantage repeatedly on the downhill test. I have had 2 runs at it so far. One warm with negligable wind, one cool with broadside 15 mph wind. This is a far cry from the 2nd Gen Prius on the same downhill.

Now device I ran originally, probably was acting like a deturbulator, as there were not many spikes, and it was wide. Apparently sail-plane pilots are experimenting with straight tapes applied close to the front of the wing, with reported benefit, as well.