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Old 01-09-2010, 02:34 PM   #6 (permalink)
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Continued from previous day

Originally Posted by aerohead View Post
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.

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.
* 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.
* 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.
* 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 -------------------------------
* The 'teardrop' represents a separation-free body of revolution of 36% thickness.
* Length/ Diameter = 2.78:1
* Frontal Area occurs @ 18% body length behind nose.
* Aft-body boat tail constitutes 82% of body length.
* At "automotive" scale,critical Reynolds Number is achieved at 20-mph.
* At 20-mph,frontal drag coefficient is constant and estimated at 0.04 in free-air.
* Frontal drag coefficient in ground-effect is estimated @ 0.08.
* Boat tail terminal angle is 22-degrees.
* When viewed in 2-D the superimposition mimics Abbott and Von Doenhoff's,"Transformation of a Circle into a Wing Section."
* By default,the form also satisfies the Kutta-Joukowsky condition for ensuring smooth flow at the trailing edge.
* The form approximates the NACA 0021 Section.
* A coincidence of the Rolex/Big-Ben form,is that it embodies W.A.Mair's critical 22-degree boat tail angle.
* The form also embodies the L/D drag minimum,as reported by Hoerner/Hucho ( see Fig.4.119,p.200,Aerodynamics of Road Vehicles,Hucho,1987.
* In the absence of more sophisticated streamlining tools,the dial-face may serve the would-be aero-modder with a design template that may be used with a high degree of confidence,much the way Volkswagen AG's handbook:"No Guesswork" aids their factory-trained technicians when entering into an overhaul.
* The "GO/NO-GO" simplicity of the clock-face-derived template makes for expeditious fabrication of pre-test prototypes,providing a historically-proven technological basis for project development.

-------- IMAGES WILL BE ADDED ASAP -----------------------------
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