MIL-HDBK-1011/2

APPENDIX C (continued)

1.3.2.6

Reynolds Number for Flow through Ductways. The Reynolds number for

flow though a long rough duct such as a long hall or corridor, R+D,, shall be

greater than 2,000.

EQUATION:

RD = LD UD/ v

(18)

where

LD is the minimum cross-sectional dimension of the duct (m), and

UD is the mean velocity through the duct (m/sec).

1.3.2.7

Reynolds Number for Flow in a Room.

The Reynolds number for flow

in a room, RR, shall be greater than 20,000.

EQUATION:

RR = LR UR/ v

(19)

where

LR is the minimum interior room dimension (m), and

UR is the maximum air speed in the room, usually equal to UW.

1.3.2.8

Reynolds Number for Flow Through Screens and Louvers. The Reynolds

number of the flow through modeled and geometrically similar screens and

louvers will never meet the minimum criteria given above. Therefore, full

size insect screens are typically used on models; and louvers are typically

modeled to a larger scale than the building so that the minimum louver

separation is 0.15 in (4 mm). In both cases, the opening dimensions are still

small relative to building dimensions, so model/full-scale flow patterns will

still be similar. Pressure loss coefficients through rooms, windows, halls,

doors are assumed to be equal for model and full-scale (if minimum Reynolds

number requirements are met). Use of full-scale insect screens and oversized

louvers ensures that the respective model and full-scale pressure loss

coefficients are equal.

1.3.2.9

Reynolds Numbers--Reducing Margin of Error. Satisfying the above

minimum Reynolds number requirements does not guarantee Reynolds number

independent results but errors will be minimized. It is good practice to use

models that are as large as possible, limited by the wind tunnel dimensions,

and to use wind velocities as great as possible, limited only by the wind

tunnel capacity.

Model Size Limitations. Model size is limited by the boundary

1.3.2.10

layer size and wind tunnel size. As mentioned earlier, the boundary layer

need not be modeled to its gradient height, but need only be modeled to a

height that fully engulfs the modeled building in question and all the nearby

buildings. The thickness of the boundary layer should be at least 200 percent

of the highest building modeled. If the models are bulky, they may be further

restricted in size by a minimum wind tunnel blockage requirement. The

projected frontal area of all buildings modeled should never exceed 10 percent

of the wind tunnel cross-sectional area.

The Reynolds number restrictions on model size often conflict with

the model height limit, the blockage requirement, and the requirement that a

significant area around the building be modeled, particularly if the building

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