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

Hi All,

I am really starting to think the 2010 Prius has flow seperation issues, in comparison to the 2nd Gen (2004 - 2009). They lowered the rake of the front of the car significantly. The front to back dimension under the hood is much bigger.

I just do not get the coast down performance I was getting from my other car (if you have not heard, my 2006 Prius was totalled by an un-trained SUV driver - lets make SUV drivers pass special training and testing! - and I am now driving a 2010). Even though the low-speed rolling resistance seems just fine, maybe even better! Yea, the car is bigger, but its also a little heavier, and yea its got those big rear-view mirrors, but they have been aero-improved with steped down rim along the back. The 2010 has a nice difuser treatment under the rear bumper. It should be a wash.

On Boundary layers, I think allot depends on vehicle shape. An aero vehicles will have a thin boundary layer, and a bluff body car will have a turbulent boundary layer. So, I think the boundary layer can probably vary by a factor of three from car to car. The thickness of the boundary layer is dependant on the tubulence energy within the air next to the vehicle. Aero-experts does this sound right ?

Hi donee -

I split this topic from where it started, in: http://ecomodder.com/forum/showthrea...tml#post202701

I assume since the subject of that thread was flow on the rear window, you're thinking the 2010 Prius has problems in the same area?

Easiest way to confirm this is tuft testing - and it truly is easy, because you can see the results in your rear view mirror!

I predict there is no flow separation on the car's back window (the upper, main one).

I'm not sure what you're referring to in terms of coastdown comparisons. Are you saying a 3rd gen Prius doesn't coast as far as a 2nd gen?

---

PS - I didn't read about losing your Prius - sorry to hear that.

Perhaps there are published Cd values out there somewhere?

According to the Vehicle Coefficient of Drag List - EcoModder , the 2010 Prius is just slightly draggier than the 2004.

And Metro is right: tuft testing is as easy as taping 4-6" pieces of yarn to your rear hatch glass with masking tape, and looking at the results in the mirror. Check it out.

Hi Metro,

Its not a problem compared to other cars. And its not in the same place as one would see on a 1 st Gen Prius (NHW-11).

But, I think its worth investigating whether the air is laying down on the roof of the 2010 Prius, and staying attached all the way to the rear spoiler.

Well, not completely. I am thinking the issue is primarily right above the driver's head. But, one might see evidence side-by-side with the tufts on the hatch window. BUt, I doubt the tuft movement on the 2010 hatch glass alone is enough to figure it out. Whichis what I can do here.

With my 2006 there was a hill I come down each day on the highway. As part of hypermiling, my goal was to be at the top of the hill at the right speed to drop into the 53 mph SHM mode when I restarted the engine at the base. I figured out that was 46 mph. Now, the 2010, at 47 mph, is down to 45 mph at the base of this same hill.

Maybe its alignement. But its not flush wheel covers, I have those on my 2010 now. Its not the grill flow, I have my license relocated across the grill on the 2010 too , now, and I have installed grill dams to prevent the blocked flow down in the grill cavity from going through the engine compartment. It should pool there, and spill out in the outboard direction.

I guess, untill I see some speed increase down this hill I am not going to be happy!!

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).

How do you know the frontal area was estimated from H x W? I don't see a source in that document.

EDIT: my mistake. I see the note at the top of that page.

But I believe the figures on that page are collected from multiple sources, and the H x W estimate may not apply to all of them. I'll have to ask Daox - he made that page....

It takes 3-5K miles to "wear-in" a new set of tires.
This can mean +2-3 MPGs.

Is it possible that new tires would also affect roll-down test speeds?

Could there also be contributions from tightish wheel bearings, etc?

:confused:

That was my first thought: tire toe-in, tighter bearings and fresher lubricants all around.

Hi Rokeby and Clev,

I am thinking Toe-in too. In that the 2010 rolls and rolls below 40 mph, in comparison to the 2006. At the higher speeds, the tires toe out, and if the toe-in setting is dead on zero, this would create scuffing friction on the tires.

The tighter bearings and non-broken in tires would impact the slow speed rolling too. If the car is rolling better at slow speeds, then other than the toe-in issue, its gotta be aero-dynamics.

I have two long slow hills on one of my routes. On the really long hill, I am at 40 mph at the top, and 36 at the bottom 1 1/2 miles later. Both cars do this exactly. On the other hill I crest at 33 mph, and at the base I am doing 35 about 1/2 mile later. Again both cars do this the same.

Slow-Speed down hill coasting wise this car is very very similar to the 2006. In the flats, I think it coasts a little better than the 2006, but I guess that is kinda subjective....

Almost all of the frontal areas are calculated from H x W. A few of them were found to be factory specifications, but very few.

I'm having trouble getting my mind around the possibility of the Gen III Prius
having worse aero than the Gen II. I'm no fan of the overall Gen III shape/look,
so it would make me happy in a perverse way if worse aero went with it...
That said, I want to believe it's something else.

I take it that the roll-downs are done in "neutral"...

Well, as neutral as a Prius gets; all the bits are still connected through
the PSD, and "neutral" is just a HSD imposed/created electronic condition.

IIRC, on the Gen II, in "neutral" there is just the slightest power being used,
~0.7 HP. I'm guessing that is to overcome drag from spinning the ICE.

Could the Gen III be using a different "neutral" algorithm so that the ICE drag
isn't compensated for?

And then, the Gen III has more aggressive regen if the roll downs were done
in D, in a "blue arrows" coast.

Hi Rokeby,

Cd can be better, but the drag worse. The Cd is not that much different between the two. That they could have changed something for the worse, yet still gotten a similar Cd. I think this is the case. Of course, as I have stated, I think its the front slope of the car that is making things worse. One might wonder if the Prius has now been turned into one of these cars with better aero drag going backwards.

The downhill runs were were warp-stealth with the peddle feathered for no regen, and minimum motor.

On the Gen III, its very easy to do this with the accelerator, thanks to the ECO display.

Not so easy on the Gen II. I would feather the peddle so that I was in warp stealth, just above regen.

I have experimented with giving the Gen III significant battery down the hill, and it still does not make up for the difference in speed.

Definitely keep a close eye on your front tires for excess wear on the outer edges. My 2006 Corolla ate up the front tires in 13k miles, and I bought it with 6 miles on the odometer.

After the typical dealer mumbo jumbo, Toyota replaced the tires for free and actually had to tweak the unibody in the rear to get the rear axle properly aligned.

If you really want to know get a reputable (non Toyota) shop to do a thorough 4 wheel alignment check. Be careful of statements like the toe is in specs, when the total toe has a spec beyond the individual wheels. Also if you have the alignment adjusted, tell them to try for minimum total toe at all 4 wheels. Not sure it that is adjustable at the rear wheels, but if so go for minimum total of all wheels.

regards
Mech

Hi OM,

Yea, the Prius does that too. We Prius people run our tires at 42/40, or a little higher in general. This will generally result in reasonable tire life. I have my 2010 at 44/42 right now cold, in the morning, before the sun hits them.

The Toe-in spec tolerance on the Prius allows toe-out. Which has been the consternation of allot of Prius drivers. I agree, minimum toe in, without going to toe-out. The rear Prius alignment is only adjustable with shims.

There is a shop near by which the owner races 911's. He has 4 wheel weights capability as well.

Hi,

I do not have direct evidence of higher rolling or aerodynamic drag with my wife's ZVW30. I'm just sharing the following:

• punctured tire - had Firestone patch and bought lifetime alignment. The toe required adjustment. I have yet to correct the passenger side camber, not as vertical as I want, and rear wheel toe and camber. These are on my list of future improvements.
• changed transaxle oil at 5k miles - the subsequent oil analysis did show evidence of sealant and manufacturing tooling material. The straight-line viscosity slope suggests 15k is the initial transaxle oil service life so I'm waiting for 15k miles (another 5k miles to go) before the second change and oil analysis.
• full block - using cardboard and duct tape, there is evidence that full blocking has a small but measurable effect. My plan is an articulating air inlet panel and side, edges to prevent air spillage out of the corners.

One unplanned change were the tires.

I picked up a second nail that hit the patch of the first tire repair. So I bought on sale, four Sumitomo T4s, the recommended, in stock, tires from the Toyota service center and run them at 50 psi (except for the recent cold front.) I'll top them off later today.

Right now, I'm conducting hill climb, maximum speed, gasoline studies with the ZVW30:

• 87 octane, E10, Shell - data collected, crest speed ~91 mph.
• 93 octane, straight gas, Pure - data collected, crest speed ~89 mph.
• 87 octane, straight gas, Pure gas - waiting on fuel exhaustion
• 89 octane, E10, Shell - waiting on fuel exhaustion

Bob Wilson

Hi Bob,

So are you saying that the 2010 Prius there is coasting down similar to your Gen 1 Prius from high speed ?

Template
 

donee,I took a factory photo of the 2nd-gen Prius and compared to the Streamlining Template and got a very close match.If there is separation over the backlight I would suspect it to be insignificant.
The boundary layer is a function of vehicle length and velocity,and the pressure profile of the pathway the air is following.It is reported by Hucho that around 20-mph,most cars will be in a turbulent boundary layer.
I have the equation to calculate boundary layer thickness although there doesn't appear to be much interest in the formulas already posted.
Our big challenge is flow separation,reducing it,or eliminating it,and Hucho asserts that this can only be accomplished by extending the length of the vehicle,improving its length/height ratio ( fineness ratio ).

Hi Aerohead,

Have you done that for the 3rd Generation Prius too? That is what I concerned about. My 2nd Generation Prius did very well down hill above 45 mph. Its the 3rd Gen Prius I have that is not.

The tail of the 3rd is close to that of the 2nd Gen Prius. Its the lead into the peak height that is different between the two cars, I believe.

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 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.

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...

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

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

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.

Hi Bob,

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

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

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.

heat but no light?
 

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.

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.

what is the weight diffgerential between a 2g and 3g prius?

Added curb weight should improve coast down speeds of the 3g prius assuming all other variables are the same.

There is a downhill grade of the interstate near my house and if i drive my mustang to 62 mph and allow myself to coast down until the next offramp, I will see 58mph.

This same distance, with a full tank of gas and about 200lbs in the trunk, will coast down and see 61mph the at the end point.

I still think your claim of a separation bubble (what you call a delamination bubble) anywhere on the roof of the car is extraordinary.

Invoking Sagan: extraordinary claims require extraordinary evidence.

If your claim (of flow separation anywhere on the roof) were true, it would be a massive mistake on the part of Toyota's aerodynamicists & designers, something I doubt would have gone un-noticed in the wind tunnel.

Speaking of which, just yesterday I was noticing the AWFUL windshield/roof transition on those fugly new Kia Souls- there's an actual sharp crease designed in right there which HAS to make for separation up there.

http://i146.photobucket.com/albums/r...a_soul_001.jpg

vs. this very nice and certainly clean transition:

http://i146.photobucket.com/albums/r...dodge-neon.jpg

Without tuft tests or a video clip of a wind tunnel test, you don't know for sure what the air is doing up there.

Although I will say- through conjecture- that since the Cd of the Gen 3 is actually better than that of the Gen 2 (AND better than most every other car on the road) that neither version is suffering from some glaring aerodynamic fault.

3rd -gen
 

donee,I've been unable to get a factory side shot of the( 3rd-gen US,4th-gen Japan),so I don't have an image of the car in true-length.Without it I can't analyze the car.
Since the new Prius has a rear spoiler,that's kind of a tip off that the backlight is a little dirty.
It also violates W.A.Mair's boat-tail architecture for attached flow.
Its 'close',and I think Prius' designers comment about being 'close to ideal' suggests that it's not 'there yet.' A standing pack of Lucky Strikes on top of the spoiler might make up the difference.
My friend already complains that at standard slope,the new Prius backlight is virtually useless as for rear visibility.:(

Hi Zonker,

Good Point. I had not been thinking about that.

But, the 2nd Gen was pretty consistent down the highway hill. The things that slowed it down was a good head wind, heavy rain or weather below 32 F.

The 2nd Gen weighed 2890 lbs (if I remember correctly), and the 3rd Gen is 3042 pounds according to the Toyota website.

I have the same stuff in the trunk of this car, as was in the trunk of the last one , minus the box the cheap socket wrenches were in. The box was mashed up good in the impact.

So, based on weight, if the drag was the same, the 3rd Gen should be coming down the hill the same or faster. Its not. With the 2nd Gen is was common for me to have to hit brakes to avoid hitting the car in front of me. With the 3rd Gen, I have to goose it to keep from getting hit from behind.

It could all be tires. But, in the meantime I want to investigate Aero.

Well,

My boss's Lexus is a .25 Cd too. And it does not look anything like a Prius.

The CdA is going to be allot bigger in the 3rd Gen by the tire widths and wider body of the 3rd Gen. Because that difference is going to be bigger than .26 / .25 .

That is a difference between the two cars aero-mod wise (both have flush hub caps, and I trialled the A-pillar turbulators with negative results on the Gen 3, and positive results on the Gen 2). My 3rd Gen has the stock rear spoiler. My 2nd Gen had a 3/8" high by 3/4 inch long "Volt bump" or so I call it, that was 24 inches long. I was going to do that, then noticed the 3rd Gen spoiler has a slightly longer upward protruding rear 1 1/2 inch. Based on that, I left it alone , thinking the Toyota engineers improved that issue already.

I do not have a camera with a long lens, to minimize paralax. So, I cannot get you a worthwhile side picture. On Prius Chat, there was a guy who took pictures of his 3rd Gen next to a 2nd Gen parked next to each. The 2nd Gen had a much squarer on-axis cross section. Which makes it more like other aero structures, than cars. The 3rd Gen is more like other cars, obviously wider than it is tall.

Do not rule out alignment. Also, I was surprised at our first, transaxle oil test ... a little more stuff in it than expected.

Bob Wilson

Hey Bob,

I had the alignment checked first off. It was fine.

How are things down there? Are you clear of the Tornados?