Page 10 - Combined_73_OCR

Gross and Sekscienski (1) hav£ published an excellent summary of

some of the more common methods of correcting for blockage. As they

point out, all methods currently used were developed for the stream­

lined shapes generally used with aircraft and are not particularly well

suited to the study of the bluff automobile bodies.

Table II presents the blockage factors as calculated and/or mea­

sured using three of the methods outlined by Gross and Sekscienski.

Pope’s method is essentially a "catch-all" method to be used when all

othe attempts to calculate or measure blockage have failed. It is

expressed as, + C X I

II
r— I
H
where Krf = Total blockage correction factor
Am = Model projected cross-sectional
area (3.06 ft2)

At = Test section area (64.5 ft2)

The correction obtained includes both wake and solid blockage ffects

and is applied to the uncorrected dynamic pressure as shown.

II

where cr = Actual test dynamic pressure

= Uncorrected test dynamic pressure

Herriot’s (4) expansion on the work of Thom (5) results in the following

xpression for blockage at low Mach Numbers.

Kt = 2K A. VM . 2C'D AM (3)
t3/2 4A

where K = Model hape factor (.98)

A = Tunnel to model shape factor (.863)

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