Anyone have 800 Lbs of clay handy? New mythbusters episode

[rrolff]

This is all great - but can someone post a pic of the dimpled mod??? I've run through the threads, and still don't see the relevance... Not that I am relevant - just wondering why and how

Laminar flow - Wikipedia, the free encyclopedia

Laminar_flow

is implemented -so I/we can test it...

[FreakinToddles]

I remember seeing an article in pop science a few months back about a company making a dimple skin for cars... MPG-Plus™, Drag Reducing Technology, Improve MPG, Vehicle Wraps, FastSkinz™

[FreakinToddles]

Ah yes, here we go Today's Mileage Tip: Turn Your Car Into a Shark - Green Car Reports

[hyo silver]

As I understand it, laminar flow is the holy grail of aerodynamics. It's relevant to just about everything that moves, and even some things that don't. The more easily air moves around objects - planes, trains, automobiles, and even buildings - the less fuel we waste.

[a64pilot]

This article may help some Laminar Flow Airfoil You don't need some type of suction to draw boundry air away from a surface to achieve laminar flow, but it is one way. Achieving perfect laminar flow is next to impossible, but as with anything getting close does have real advantages. In the wind tunnel both the B-24 and the P-51 did real well, but in reality manufacturing tolerences, dirty surfaces from operating off of grass strips etc. kept either from achieving laminar flow, but the P-51's real sucess came from it's great range, something it wouldn't have had without that wing.

[a64pilot]

The idea of a rough surface having less drag than a polished one is in theory the rough surface would "hold" the boundry layer of air stationary against the object and the drag would come from one layer of air "shearing" against another layer of air.
A smooth surface on the other hand would have airflow across the smooth surface. Which generates the most drag? I don't know.
I do know for sure that it is normal and easily demonstrated that a well waxed and polished airplane is faster than the exact same airplane is dirty.
What do the dimples on a golf ball do? Well, they are vortex generators Aerospaceweb.org | Ask Us - Golf Ball Dimples & Drag
Like those thing some of you called "roof fins"

[a64pilot]

If somebody really wanted to get serious with this, all you need to determine when airflow separation occurs is a ball of yarn and a roll of scotch tape. You would be surprised how accurate "tufting" a vehicle is.
I would theorize that the lower the CD of a vehicle you have, the less possible gain there would be from using vortex generators to increase the laminar flow.

[qbee42]

What we need is thicker air. If we can replace air with a low Reynolds number fluid it will be easy to get laminar flow.

Tom

[dogfriend]

Originally Posted by qbee42

What we need is thicker air. If we can replace air with a low Reynolds number fluid it will be easy to get laminar flow.

Tom

The Los Angeles basin. You can actually see the air on a summer day.

[donee]

Hi All,

This has been discussed some on ecomodder. Which is probably the best collection of amateur drag reduction aerodynamics knowedge regarding cars on the internet. They accepted based on the show that an actual improvement in fuel economy occured.

The best reason I have read on there as to why, is that the Ford Taurus used, has the rear window at the worse possible drop angle for aerodynamics. It turns out that you need to keep that angle below about 20 degrees (like a Prius), or greater than 50 degrees for the best drag. This is a published professional aerodynacist result (Hucho?).

Consequently, the flow is seperating on the back glass. And conseqeuntly the dimples helped by delaying the seperation till its flow cross section was less than the cross section of the laminar flow boundary layer further forward on the car.

Some words have been put out. Such as "Bluff". There are very few cars that are not Bluff bodies . The Golf ball is a Bluff body. These are both the same type of animals aerodynamically. Cars can benefit from bluff-body aerodynamics tricks.

Even though the older Taurus looked aerodynamic, it apparently is not.

Fast skinz is a sham. Its been proven not to work. In the Mythbusters episode they were careful to scale the dimples to the same relative size of the car, as they are on a golfball. Shark skin works on ships, where the flow is hydrodynamic. It also works on high-subsonic jets - where apparently the Reynolds number is similar. Its been said that for aerodynamic ground vehicles (such a an Aptera) that the speed would have to be in excess of 250 mph to get into that same aerodynamic regime as a + 20 knot boat hull/fish and high sub-sonic jets. A typical car, even a Prius will always be a bluff body however.