The Venturi effect is simply the drop in wind pressure when it passes through a confined section.
In wind flow analysis, the Venturi effect can help explain the wind flow behavior and high gusts through walkways when passing between two high-rise structures.
A phenomenon like high gusts or vortex shedding can be visualized in CFD simulation, thus, designs can be optimized for the best results.
Example of a simulation showing how the Venturi effect can change the flow behavior of a fluid
In nature, some constrictions that obstruct or change the way a fluid flows can be observed. One example is the wind blowing through mountain passes where the speed and intensity of the flow are stronger. This similar mechanism is engineered through many flow devices that affect our daily lives, such as ventilator systems, spray cans, or vacuum cleaners. The basic idea behind this is through the introduction of a bottleneck so that the flow can exhibit an increase or decrease in pressure depending upon the change in its speed.
In the design of structures where wind flow can be a hurdle, the Venturi effect is an important concept in wind flow analysis and is explored in detail with CFD simulations. In this article, we will explore the Venturi effect for wind flow analysis.
What Is the Venturi Effect?
Take the above diagram as an example. The two ends of the tube are connected midway with a constricted section with a smaller cross-section. When the air or fluid passes through this constricted area, the velocity increases. This satisfies the continuity equation in fluid dynamics, according to which the mass entering the system and exiting it should be equal. Similarly, the pressure drops while the velocity rises in the constriction. This is the Venturi effect. This increase in velocity and decrease of pressure occurs in accordance with the principle of conservation of energy. This is also called Bernoulli's principle. In order for these principles to be valid, the fluid must adhere to the following requirements:
The fluid must be inviscid and incompressible
The flow must be laminar
The flow must be driven by the pressure drop
The pressure gradient for the flow satisfying the above requirements can be expressed mathematically as:
Note that p1 and p2 represent the pressure at either section of the constriction, ρ is the fluid density, and v1 and v2 represent the velocity at the inlet and outlet of the tube. The volumetric flow rate through the Venturi tube can then be easily calculated as:
Q is the flow rate for cross-sections A1 and A2 of the tube and constriction, respectively.
The Venturi Effect and Wind Flow Analysis
The Venturi effect in wind flow analysis is of significant importance when studying the aerodynamics of high-rises, wind tunnels, or other similar structures. Since these structures act as the confinements affecting the free flow of air, the velocity of wind may increase around the buildings or along the pedestrian passage. The Venturi effect, the behavior of the velocity drop and rise when wind is passing through a constricted area, can be studied to eliminate discomfort like high gusts in pedestrian regions and incorporated into the design so as to create natural ventilation.
Wind analysis also points toward the different loading conditions which the wind flow can exert on a structure, resulting in vortex shedding and interfering with the structure’s natural frequency. The oscillations resulting from vortex shedding can result in structural failure, so, eliminating this effect is important during the design process. The analysis of these forces, velocities, and frequencies of the wind and their effect on a structure can be assessed with computational fluid dynamics (CFD).
Simulating the Venturi Effect and Wind Flow Problems With CFD
CFD simulation can help engineers understand the Venturi effect, wind flow patterns, and loading conditions in the design of complex structures. The state of flow near the constriction or the possibility of vortex shedding can be analyzed by running different iterations of CFD simulations. The negative frequency observed in a structure can then be eliminated by making changes in the design. The Venturi effect can be analyzed with the visualization of flow patterns, which is instrumental in ventilation system designs in buildings and pedestrian walkways in urban settings.
CFD simulation software such as the Fidelity 3D Solver can not only design a detailed simulation but also numerically analyze the pressure drop and flow rate, the key influencing factors for the Venturi effect in wind. With the high-fidelity simulation of wind flow behavior and load conditions, a safer structural design can be ensured.