CPP’s Dr. Petersen and Dr. Guerra address flaws in building downwash program

CPP advances its reputation as an essential voice and leader in the wind engineering and environmental industries.

The paper PRIME2: Development and evaluation of improved building downwash algorithms for rectangular and streamlined structures, written by CPP’s Dr. Ron Petersen and Dr. Sergio Guerra, is now published in Journal of Wind Engineering & Industrial Aerodynamics.

The paper presents the results of an industry funded research study that initiated in late 2016 with the following objectives: 1) Correct the known problems in the PRIME theory; 2) Incorporate and advance the current state of science; 3) Expand the types of structures that can be accurately handled (e.g., streamlined, long, wide); 4) Properly document and verify the model formulation and code for the updated PRIME (PRIME2); 5) Collaborate with EPA to work toward implementing the improved model.

The research effort included a literature review, wind tunnel testing, data analysis, new theory development, updating of the current PRIME model code and evaluation of the new model, AERMOD/PRIME2, against field databases. For the wind tunnel testing, velocity and turbulence measurements were obtained downwind of three rectangular buildings and two streamlined structures for three different approach turbulence conditions. Based on those measurements, new equations were developed to estimate the velocity deficit and turbulence intensity increase in the building wake as a function of downwind distance, height above ground, building shape, and approach turbulence intensity (or roughness).

The study has proven that the current equations used in the EPA approved building downwash program, PRIME, are flawed. The new equations correct these flaws and have the following features that are not currently addressed in PRIME.

  • Building wake effects decay rapidly back to ambient levels above the top of the building versus the current theory that has these effects extending up to 3 building heights.
  • Lateral turbulence enhancement in the wake is less than vertical turbulence enhancement (currently PRIME has them identical).
  • The approach turbulence and wind speed is calculated at a more appropriate height versus the current theory where half the wake height at 15 building heights downwind of the building is used.
  • Wake effects for streamlined structures are reduced.
  • Wake effects decrease as approach roughness increases.

Results of AERMOD/PRIME2 comparisons with field observations will be provided in a forthcoming journal article. CPP is currently working with EPA ORD and OAQPS to develop a mechanism for including these improvements into the regulatory approved version of AERMOD

The Journal of Wind Engineering & Industrial Aerodynamics publishes and exchanges information on all aspects of wind engineering included in the activities of the International Association for Wind Engineering.

Access the paper here.