Enviroware

Odor screening tool

Stack-tip downwash

Estimate the reduced effective stack height when exit velocity is low compared with wind speed at stack height.

Open calculator Odor assessment services
  • Briggs algorithm
  • Point sources
  • Exit velocity check
  • LAPMOD reference
Stack-tip downwash Tool
Stack-tip downwash schematic
The correction lowers the starting height for plume rise when stack-tip downwash conditions are present.

Calculator

Enter stack and wind data.

m above ground level.
m internal diameter.
m/s at the stack outlet.
m/s at the top of the stack.
Fill in the form and calculate the result.

Limits

A screening correction for simple stack checks.

Stack-tip downwash can occur when the wake of the stack draws the plume downward, reducing plume rise and increasing near-source concentrations. Site-specific assessments still require full source data and dispersion modeling.

  1. 01
    Velocity ratio
    The correction is applied only when exit velocity divided by wind speed is lower than 1.5.
  2. 02
    Wind at stack height
    Use wind speed representative of the stack top, not a generic ground-level value.