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Downwash Analyst |
  
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Downwash Analyst |
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BREEZE Downwash Analyst is a tool to help AERMOD dispersion modelers 1) visualize and better understand how BPIP (Building Profile Input Program) generates the BPIPs (Building Profile Input Parameters) used by PRIME (Plume Rise and Building Downwash Model), and 2) visualize and better understand how the BPIPs are used by PRIME to compute the cavity and wake geometry used to modify plumes (i.e. induce downwash) within AERMOD.
In general, the BPIP processor produces two results:
| 1. | The maximum GEP (Good Engineering Practice) stack height for each stack as a function of the neighboring building geometry and 1440 wind directions. |
| 2. | The maximum HWE (Height of Wake Effect) and the BPIPs (Building Profile Input Parameters - height, width, length, X-shift, and Y-shift) for 36 wind directions around each stack. |
The information derived while computing the maximum GEP heights is later used to compute the maximum HWEs and BPIPs. The computation of both results follow a similar procedure:
If, for a given wind direction, there are no building tiers directly upwind or immediately downwind of a stack, the stack GEP height or HWE and BPIPs are set to zero. For a single tier near a stack, BPIP computes the tier's profile parameters and SIZ (Structure Influence Zone - GEP-SIZ when computing GEP heights and HWE-SIZ when computing HWE and BPIPs) for each wind direction around the stack. Each time (i.e. each wind direction) the stack is within the tier's SIZ, the GEP height or HWE and BPIPs are computed and saved. Otherwise, all are set to zero. When multiple tiers are in the vicinity of a stack, BPIP computes profile parameters and SIZs for all possible tier-group combinations and determines which single-tier or tier-group produces the highest GEP height or HWE for each wind direction. Like before, each time (i.e. each wind direction) the stack is within a single-tier's or tier-group's SIZ, the GEP height or HWE and BPIPs are computed. The GEP height or HWE and BPIPs of the single-tier or tier-group that produces the highest GEP or HWE are saved. Otherwise, all are set to zero.
Though the entire two-step process is relatively complicated, the BREEZE Downwash Analyst provides a simple way to visually observe how BPIP locates stacks within the GEP-SIZs and HWE-SIZs of the single-tiers or tier-groups that produce the maximum GEP heights or HWEs, for every wind direction.
BPIP Analysis Modes
BPIP GEP - Select Stack & Wind Direction - Displays the single-tier or tier-group, with it's GEP-SIZ, that produces the maximum GEP stack height for a selected stack and a selected wind direction.
BPIP GEP Max - Select Stack - Displays the single-tier or tier-group, with it's GEP-SIZ, and the single wind direction that produces the maximum GEP height for a selected stack.
BPIP HWE - Select Stack & Wind Direction - Displays the single-tier or tier-group, with it's HWE-SIZ, that produces the maximum HWE for a selected stack and a selected wind direction.
BPIP Output - Select Stack & Wind Direction - Displays the single-tier or tier-group that produces the maximum HWE and it's corresponding BPIPs (i.e. profile box with height, width, length, and X,Y offsets) for a selected stack and a selected wind direction. The single-tier or tier-group BPIPs are the BPIP output data that is subsequently used by the PRIME Plume Rise and Building Downwash Model.
PRIME Analysis Mode
PRM Plume - Select Stack & Time - Use BREEZE AERMOD to generate a PRIME plume downwash file (see the AERMOD | Input Menu | Output Options | Other File & Options). Load the file into Downwash Analyst to observe how the BPIP building profile parameters are used to generate the wake boundary, cavity boundary, and downwash-modified plume. Observe all hourly downwash (i.e. plume) geometry by selecting both a stack and a time, in either the 3D Display or the side-view Chart display.
Page url: http://www.breeze-software.com/prod/aermod-isc/help/index.html?downwash_analysis.htm