View Single Post
Old 01-08-2010, 07:02 PM   #5 (permalink)
aerohead
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 11,742
Thanks: 18,906
Thanked 6,089 Times in 3,733 Posts
Superimposition ( Rolex meets Big-Ben )

Just greasing the wheels for tomorrow.
I finally put some graphics together for this thread.The "word-pictures" seem to hit dead-ends,so between wearing out Al's copy machines,a pair of scissors,White-out,and Scotch Tape,I've finally got something to sink our eyes into.
There's been enough talk of golf-ball dimples,turbulent boundary layers and critical Reynolds Numbers that maybe we can make a connection to all this now.
THEORY Re-hash:
* All spheres behave identically above critical Reynolds Number,regardless of size.
* Spheres are so well understood that they may be used as calibration models for any wind tunnel.
*The 'fixed' separation point of a sphere offers a naturally defined turbulence-free architecture by employing a single superimposition,as Salvador Dali might do with one of his canvases.
*Familiar forms we can use to visualize the the superimposition are the dial face of both the analog wristwatch,and wall clock.

CONDITIONS:
The "flow" conditions for our example can be interpreted either as a dial face moving horizontally to the left,with the forward stagnation point located at 9:00 O'clock,or the dial face stationary,as in a wind tunnel,with the air blowing horizontally from the left.In both instances,air velocities are such to produce Reynolds Number above critical.
RESULTS:
* In all situations,attached flow exists from the forward stagnation point,up and over,to a point at 115-degrees of rotation,occurring both at 4-seconds after 12:00 and 6:00( down and under ).
* Photographs of this flow can be seen in the FLOW-IMAGES thread galleries for both air and water.Golf-ball images can be GOOGLED.
SUPERIMPOSITION
* The area of the sphere's aft-body,between 12/6 and 4-seconds after is what is of interest to aero-modders
* Enlargement and enhancement of this section can provide the architecture for a separation -free automotive roof and aftbody structure.
* Suitable enlargement and superimposition of a properly-scaled smaller watch dial "leading-edge" creates a proto-teardrop of which the aft-body may serve as a design template.
OUTCOME
* The teardrop created possesses the hemispherical nose reported in fluid texts to provide adequate and minimum low drag,separation-free penetration for up to transonic velocity.
* The teardrop's aft-body is also separation-free and may be used with high-confidence as a template for modeling automotive forms.
-------------------- WILL CONTINUE -------------------------------
  Reply With Quote