Observations on LB turbulence

[GeneW]

Noticed on the way home that my rear window gets dirty very fast. I'd be willing to speculate that the laminar air flow over the car does not recombine near the tail, leading to vortices just behind the hatch.

Wonder whether some sort of base bleed or disruption of flow near the hatch might improve drag characteristics?

Gene

[eTiMaGo]

several people have messed around with vortex generators but I have no idea if they did any actual aerodynamic testing :laugh:

Due to the sudden dropoff of the rear hatch, we can't expect great aerodynamics back there sadly, it is one of the drawbacks of the hatchback form factor. Spoilers can only help so much, I have one but the rear glass still turns to a mess real fast...

[jclo3313]

It's a Yaris man. How much of your driving is done above 55mph? The DCOE really doesn't matter that much for in town driving. To clear your back window of excess debris you could add a downward facing wind deflectoe similar to that used on an SUV.

[TheUnGroomed]

On Friday I did some driving in some light snow and I saw a little bit of a swirl back there. I guess if a spoiler could be extended to keep the air attached, it could help keep the window clean.

[metalshark]

actually Gene the turbulence doesn't seem that bad, at least it is symmetrical in nature, I've driven behind many Yarii here in Montreal both in snow and rain conditions. I admit the window gets dirty pretty fast. However if you have a chance to see a Yaris in rain from behind you will notice that the airflow goes around rather nicely and evenly. In my Yaris' case my fin antenna seems to help split the air evenly, but it might just be me
When I was in college I asked a Prof about the vehicular aerodynamics. He said for the airflow to recombine in laminar flow behind a car the boat tail would have to be 20' long. I guess that's why the EV1 and the '99 Buick Rive do so well in a wind tunnel. That's why my Pinto was more aerodynamic placed backward in the tunnel than it was in its normal mode of travel. There wasn't any NHRA rules preventing backwards body placement but no one competed that way.

[Phaeton]

I noticed a slight improvement when I added the lip spoiler, but the back window still gets pretty dirty.

[BailOut]

I cut roughly half of the accumulation on and half of the misting behind my LB simply by adding on the OEM mud flaps. That means that much of the turbulence comes from underneath the car.

[GeneW]

I cut roughly half of the accumulation on and half of the misting behind my LB simply by adding on the OEM mud flaps. That means that much of the turbulence comes from underneath the car.

Are you being ironic, Brian? :)

Could also mean that most of the crap comes from the rear wheels, which when you vent it downwards doesn't contaminate the rear glass.

Gene

[Bob_VT]

Noticed on the way home that my rear window gets dirty very fast. I'd be willing to speculate that the laminar air flow over the car does not recombine near the tail, leading to vortices just behind the hatch.

Wonder whether some sort of base bleed or disruption of flow near the hatch might improve drag characteristics?

Gene

Gene...... have you ever considered driving for an entire week in reverse? Do you think the front end would suffer the same contaminated fate? :iono:

I have the small (tiny) factory lip spoiler and that seems to take the brunt of the dirt (where the rain does not hit).

It is a vacuum back there. I have noticed when I do a complete glass cleaning that the dirt from the back window is blackened from the exhaust fumes.

Just one of those things we have to endure....... until you report back on the reverse drivinf technique! :wink:

[BailOut]

Are you being ironic, Brian? :)

Could also mean that most of the crap comes from the rear wheels, which when you vent it downwards doesn't contaminate the rear glass.

Gene

No, there is no irony there. :smile: I did not expect that kind of result from adding the mud flaps but I got it.

[GeneW]

Gene...... have you ever considered driving for an entire week in reverse? Do you think the front end would suffer the same contaminated fate? :iono:

I've been told with US ATs that several miles worth of reverse driving will destroy the transmission. Something to do with the pump not running properly in reverse.

Think I'll pass on seeing whether Toyota considering driving backwards for long periods of time to be "abuse" under the warranty.

It is a vacuum back there. I have noticed when I do a complete glass cleaning that the dirt from the back window is blackened from the exhaust fumes.

Just one of those things we have to endure....... until you report back on the reverse drivinf technique! :wink:

Base bleed.... Use a belly pan to convey ram air into the back section, delivering pressure to the rear area.

Gene

[TLyttle]

Agreed, but be careful. Belly pans can play their own mean tricks to the aerodynamics of a car!

"Filling in" that vacuum can be accomplished in a few ways, but smooth air is mandatory for the best results. I contend that the good mileage I get is because of the shape of our sedan: the extra length ("... 20' long...") and slope of the back is better streamlining than the blunt rear on the hatch. The rear window doesn't get dirty for the same reasons. So the chore becomes, making the air think you are driving a sedan, and I really think it takes a wind tunnel to do that properly, rather than with the wannabe aerodynamic packages available now.

[KCALB SIRAY]

I use this handy dandy doohicky. I get amazing results and sometimes a compliment or two:iono:

[GeneW]

I have a wiper. I thought that the deposit of road gunk - mainly calcium chloride and sodium chloride that also eats Yaris - was an artifact of drag.

Thanks to TLyttle about the word on belly pans. I had forgotten that nasty thing called "Ground Effect". That's all I need, to have the damn thing float!

Gene

[TLyttle]

Funny thing about vacuum: it doesn't really care where the air comes from, and under the car is as good a place as any, hence the accumulation on the back window. Decades ago, I had an old Volvo wagon whose roof design didn't allow for a deflector over the rear door, so I used two small aftermarket deflectors, one each side, to infill the rear window. It certainly created some weird mud patterns, but it did keep the window relatively clear.

The mudflaps also change the air patterns in a positive way, but I am not sure how much drag that would add. You just know that someone will think, "Whut's good, more's better", and add a full-width mudflap; it might just work. Like I said, a tunnel would tell all.

And "floating" can be very disturbing alright! I built an aluminum duner in the 60s, and the front fenders had a tendency to lighten up the car at ~75mph. First hint was the steering being ineffective. Nerve wracking....

[HTM Yaris]

Use the poor mans wind tunnel . Use surveyors tape to make streamers . Of course you will have to elevate the streamers about 1 " from the surface . Then follow your car while videoing the sequence .

I've thought about using CF canards right in front of the tail lights to create more downforce , but you could easily redirect .

[sketch182]

I have had many a hatchback including a VW Rabbit, AMC Gremiln, smart car and Yaris. All of them have pulled the road moisture onto the back window. The wiper is the best solution.

[CCILovePinkCC]

I do have to use the wiper on the back window quite a bit.
I didn't realize that all Yari (yep, I say the plural for Yaris is Yari) don't have wipers on the back.

[metalshark]

I cut roughly half of the accumulation on and half of the misting behind my LB simply by adding on the OEM mud flaps. That means that much of the turbulence comes from underneath the car.

Way back 40 years ago several road racer types cut their times a lot by smoothing under car air flow. Its such a good trick that NASCAR requires you to use stock floor pans when you build a car. Some racers modified floor pans to create large down forces at speed. Great in the turns......unless you suddenly loose that suction for some reason.