Technical Notebook: The Venturi Effect

Insurance claims personnel are often asked to consider whether damage to a building is related to excessive wind forces or whether a structure is deficient in its capacity to resist wind.  Extending or denying wind damage related coverage is linked to the expected wind loading on a structure. Wind velocity data is often obtained from weather station reports obtained from instrumentation in open country. This data may or may not be reflective of the actual wind speed at the claimant’s loss site.  A wind speed of 70 mph may not be sufficient to cause damage to the claimant’s properly designed and maintained structure, yet a wind speed of 90 mph may be damaging.  A condition at the loss site that can cause higher wind speeds than that reflected by open country wind speed data is called the Venturi effect.

Named after physicist Giovanni Venturi (1746-1822), the Venturi effect refers to the increase in velocity of a fluid as it travels through a restricted area. Figure 1 below depicts a fluid (air, water, and so on) traveling at an initial velocity. As the fluid reaches the restricted area (throat, Venturi), the velocity increases based on the principle of continuity. As a refresher, the principle of continuity states that mass flow through these areas must remain constant. As the fluid exits the restricted area, the velocity returns to a more nominal value.