126.96.36.199.1 Calculating the plume height for wake effects determination.
The building downwash algorithms in the ISC models always require the calculation of a distance dependent momentum plume rise. When building downwash is being simulated, the equations described above are used to calculate a distance dependent momentum plume rise at a distance of two building heights downwind from the leeward edge of the building. However, stack‑tip downwash is not used when performing this calculation (i.e. hs´ = hs). This wake plume height is compared to the wake height based on the good engineering practice (GEP) formula to determine whether the building wake effects apply to the plume for that hour.
The procedures used to account for the effects of building downwash are discussed more fully in Section 188.8.131.52. The plume rise calculations used with the Schulman‑Scire algorithm are discussed in Section 184.108.40.206.
220.127.116.11 Plume Rise When Schulman and Scire Building Downwash is Selected.
The Schulman‑Scire downwash algorithms are used by the ISC models when the stack height is less than the building height plus one half of the lesser of the building height or width. When these criteria are met, the ISC models estimate plume rise during building downwash conditions following the suggestion of Scire and Schulman (1980). The plume rise during building downwash conditions is reduced due to the initial dilution of the plume with ambient air.
The plume rise is estimated as follows. The initial dimensions of the downwashed plume are approximated by a line source of length Ly and depth 2Ro where:
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 - 26 - 27 - 28 - 29 - 30 - 31 - 32 - 33 - 34 - 35 - 36 - 37 - 38 - 39 - 40 - 41 - 42 - 43 - 44 - 45 - 46 - 47 - 48 - 49 - 50
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