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1.1.5.3.2 Schulman and Scire refined building downwash procedures.

     The procedures for treating building wake effects include the use of the Schulman and Scire downwash method.  The building wake procedures only use the Schulman and Scire method when the physical stack height is less than hb + 0.5 LB, where hb is the building height and LB is the lesser of the building height or width.  In regulatory applications, the maximum projected width is used.  The features of the Schulman and Scire method are: (1) reduced plume rise due to initial plume dilution, (2) enhanced vertical plume spread as a linear function of the effective plume height, and (3) specification of building dimensions as a function of wind direction.  The reduced plume rise equations were previously described in Section 1.1.4.11.

     When the Schulman and Scire method is used, the ISC dispersion models specify a linear decay factor, to be included in the σz's calculated using Equations (1‑37) and (1‑38), as follows:

where σz´ is from either Equation (1‑37) or (1‑38) and A is the linear decay factor determined as follows:

where the plume height, he, is the height due to gradual momentum rise at 2 hb used to check for wake effects.  The effect of the linear decay factor is illustrated in Figure 1‑1.  For Schulman‑Scire downwash cases, the linear decay term is also used in calculating the vertical virtual distances with Equations (1‑40) to (1‑41).

 

 

 

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