1. Air Curtain Effect using Multi-Phase Fluid  Flow Analysis

When entering a department store or building through an open doorway, you may experience a strong downward airflow. This phenomenon is known as the air curtain effect, where a high-velocity downward air stream is generated to minimize the mixing of indoor and outdoor air.

Liquids and gases do not maintain a fixed shape. Instead, they move along walls or are transported by the surrounding fluid flow. In this example, a multiphase flow approach is used to investigate changes in liquid behavior when a liquid–gas interface is formed.


 

2. Why Use Multi-Phase Fluid Flow Analysis?

Conventional fluid flow analysis generally assumes a single fluid phase. However, when multiple fluids coexist, their interactions must be considered. Depending on whether the interface between fluids is maintained, the flow can be categorized as either multiphase flow or mixture flow.

In multiphase flow analysis, accurately capturing the interface between fluids is critical. To represent this interface, methods such as the Level Set Method and the Volume of Fluid (VOF) Method are commonly used.

The Level Set Method is particularly suitable when there is a significant density difference between the two fluids. For example, when analyzing liquid–gas systems with density ratios exceeding 1,000:1, the low-density gas phase can often be simplified, improving computational efficiency. This method is widely used for general liquid–gas interface simulations and can significantly reduce computational costs.

In contrast, the VOF Method calculates the interface by considering the physical properties of both fluids and is well suited for cases where density differences are smaller. For highly detailed simulations involving water–oil interfaces or gas–liquid systems where fluid velocity fields must be accurately resolved, the VOF method is generally preferred. Therefore, selecting the appropriate method based on both accuracy requirements and computational efficiency is essential.

3. What should be considered in Multi-Phase Fluid Flow Analysis for Air Curtain Applications?

To achieve an effective air curtain effect, maintaining a stable gas flow is essential. In department stores and building entrances, cross-flow fan–based air curtains are commonly used to control airflow and generate a strong downward air stream. This airflow is produced by mechanical power and is designed to reduce air exchange between indoor and outdoor environments.

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