# Numerical and Experimental Characterization of a Coanda-Type Industrial Air Amplifier
## 1 Introduction  
Continuous airflow generation is crucial in a wide range of mass flow rates, ranging from high-performance jet propulsion engines to everyday handheld hairdryers. It may be produced passively by pressure gradients or actively by mechanical means, the latter involving the modification of the flow momentum through moving parts [1]. However, when these air propulsion systems work in a centralized manner (i.e., airflow is generated far from the place where it is required), they lack energy efficiency due to pressure losses in the air ducts [2]. Fortunately, forced airflow can also be provided by decentralized systems, allowing for the generation of the required mass flow range closer to the place where it is needed. In particular, this may be achieved by using air amplifiers. Air amplifiers are capable of generating airflow when powered by a smaller primary airflow, as they provide a final mass flow rate significantly higher than the primary one. Primary flow is circulated through a region where it expands, creating a zone of very low pressure, causing the surrounding upstream fluid to be entrained and generating a secondary flow. These two flows mix and are expelled downstream at high speed. The flow phenomenon responsible for entraining the secondary flow is attributed to the so-called Coanda effect, which is the ability of a flow to follow a curved contour without separation [3]. The Coanda effect has been extensively investigated experimentally in jets on aerodynamic surfaces, leading to a better understanding of the physical phenomenon [4; 5; 6; 7; 8]. Furthermore, the theoretical and experimental studies of [PERSON] [9] about the Coanda effect on ejectors led him to develop a mathematical model to predict the performance of thesedevices. These investigations have provided valuable information on the development and optimization of air amplifiers. The change in momentum of the primary flow may be achieved by several means. Most air amplifiers require compressed air to work, which might be supplied externally from pressure lines connected to stored compressed air tanks. In addition, as in the case of some commercial products [10], an impeller installed inside the air amplifier casing is responsible for the supply of compressed air. In contrast, several authors have proposed air amplifiers based on electrohydrodynamics (EHD) [11]. Instead of supplying compressed air, they propose the generation of accelerated primary flow, i.e., ionic wind in this case, using local high-voltage fields that require an external electrical supply. While this approach maintains the advantage of not having moving parts, thus reducing maintenance costs, one of the main drawbacks is that the primary flow rate is limited by the electrical supply and the space occupied by the wiring system. Commercial air amplifiers powered by highly compressed air provide more uniform airflow than other devices. Also, since they do not have moving parts and do not require electrical power, they are long-lasting devices. As a consequence, air amplifiers are a great solution for many applications. They have been proposed as alternatives in industrial environments to cool systems (i.e., data centers and battery packs) [12], distribute heat in molds, ventile welding fumes, and suppress dust [12; 13; 14]. Air amplifiers are also used for air purification and humidification in confined areas [15] but have also been proposed to be employed in landfill aeration systems [16]. Their use in scientific research has been proven to be effective in improving the efficiency of mass spectrometers [17; 18; 19]. Regardless of how the primary flow is generated, the working principle of air amplifiers is the same. On air-supplied air amplifiers, the process is as follows: The high-pressure flow is first injected into an annular chamber near the inflow region (see Figure 1), where it is distributed and reoriented for its ejection through a thin ring gap at high speed, producing the high-momentum primary flow.