💨 Wind Engineering Terminology Glossary (Non-Table Format)

This glossary defines key terms and concepts used in the study of the interaction between wind and the built environment, including aerodynamics, fluid dynamics, and structural dynamics, presented in a clear, list-based format.

I. Fundamental Aerodynamics & Fluid Flow

  • Aerodynamics: The study of the motion of air and its interaction with a solid object.
  • Atmospheric Boundary Layer: The lowest layer of air in the troposphere (about one km thick) where the ground surface (land or sea) influences the behavior of atmospheric flows.
  • Blockage Effect Distortion effect of wind tunnel walls on measurements, particularly force and pressure measurements.
  • Bluff Body A body with a large frontal dimension, from which the airflow separates.
  • Boundary Layer The region of reduced air velocities near the ground or the surface of a body.
  • Boundary Layer Wind Tunnel A testing section with flow characteristics that mimics a target full-scale boundary layer used to study the effects of wind on the built environment.
  • Computational Fluid Dynamics (CFD) A branch of fluid mechanics that uses numerical analysis and algorithms (like Large Eddy Simulations, LES) to simulate the interaction of fluids with surfaces defined by boundary conditions.
  • Drag The force exerted on a body along-wind.
  • Lift The force exerted on a body cross-wind, usually (but not necessarily) vertical.
  • Reynolds Number The ratio of inertial forces to viscous forces in fluid flow.
  • Separation In bluff body aerodynamics, flow separation occurs when the boundary layer travels against an adverse pressure gradient, causing the fluid flow to detach from the object's surface and form eddies and vortices.
  • Strouhal Number A non-dimensional parameter representing the vortex-shedding frequency.
  • Vortex Shedding The periodic shedding of eddies formed from the rolling-up of the boundary layer shed from a bluff body.
  • Wake The region of low velocity and turbulent flow in the region downstream of a body.
  • Turbulence Fluctuations in fluid flow. In meteorology and wind engineering the term 'gustiness' is also used.

II. Structural Response & Dynamic Effects

  • Aerodynamic Damping: Aerodynamic forces proportional to the velocity of a structure, which add to (or subtract from) the structural damping.
  • Aeroelasticity The study of the interactions among inertial, elastic, and aerodynamic forces.
  • Cauchy Number Ratio of internal forces in a structure to inertial forces in the air.
  • Flutter One-, or two-, degree-of-freedom aeroelastic instability, involving rotational motion.
  • Galloping Single-degree-of-freedom aerodynamic instability found with flexible structures (typically square, rectangular, or D-sections). There is a potential if the Den Hartog criterion is met.
  • Gust Response Factor Ratio of the expected maximum structural response to the mean structural response.
  • Lock-in The enhancement of fluctuating forces produced by vortex shedding due to the motion of the vibrating body.
  • Scruton Number A non-dimensional parameter incorporating the ratio of structural mass to fluid mass, and structural damping, which measures a structure's propensity for resonant dynamic response.
  • Spectral Density A measure of the contribution to a fluctuating quantity (e.g., deflection) within a defined frequency bandwidth.

III. Meteorological & Statistical Terms

  • Correlation Statistical relationship between two fluctuating random variables.
  • Froude Number Ratio of inertial forces in the air to gravity forces.
  • Gust Factor Ratio of the expected maximum to mean value of wind speed, pressure, or force.
  • Gust Response Factor Ratio of expected maximum to mean structural response.
  • Integral Scale (L) A characteristic length representing the average size of turbulent eddies or gusts in the atmospheric boundary layer.
  • Jensen Number Ratio of building dimension (usually height) to roughness length in atmospheric boundary-layer flow.
  • Logarithmic Law A mathematical representation of the profile of mean velocity with height in the lower part of the atmospheric boundary layer.
  • Mean Wind Speed The average speed of wind flow expressed over a variety of averaging times (e.g., fastest mile, one-minute mean, mean hourly).
  • Peak Factor Ratio of maximum minus mean value, to standard deviation, for wind velocity, pressure, force or response.
  • Peak Gust Maximum value of wind speed in a defined time period.
  • Pressure Coefficient Surface pressure made non-dimensional by the dynamic pressure in the wind flow.
  • Return Period Inverse of the probability of exceedence of an extreme value.
  • Roughness Length A measure of the aerodynamic roughness of a surface, which affects the boundary-layer flow over it.
  • Saffir-Simpson Scale A one-to-five rating based on a hurricane's sustained wind speed (one-min average measured over water at ten meters height).
  • Stationary Description of a random process whose statistical properties do not change with time.
  • Three-Second Gust The highest sustained gust over a three-second period. In the US, the design wind speed is typically based on this value.
  • Thunderstorm Thermally driven local storm capable of producing strong downdraft winds.
  • Tornado Local intense storm formed from thunderclouds, with intense winds rotating around a vortex structure.
  • Tropical Cyclone An intense tropical storm (generic name) which can occur over warm tropical oceans, incorporating 'hurricane' and 'typhoon'.
  • Wind Axes Axes parallel and normal to the mean wind direction.

📜 References

  • Holmes, D.J. (2015). Wind Loading of Structures. Third Edition. CRC Press.
  • Simiu, E. and Scanlan, R.H. (1996), Wind Effects on Structures: Fundamentals and Applications to Design, John Wiley & Sons, Inc., New York.