Simulation Analysis of a Coanda-Effect Ejector Using CFD

Abstract

This work presents the optimization of a Coandă-effect air ejector used widely in industry through computational fluid dynamics. This optimization was developed in ANSYS FLUENT® software V16.2. Two 3D models of the commercial ejector (ZH30-X185 by SMC®) were carried out for the simulation procedure, varying the size of the separation of 0.3 and 0.8 mm in the walls of the nozzle, which communicates the high-pressure region and the mixture zone. In the experiment designed, the feed pressure applied to the ejector take values of 0.20, 0.25, and 0.30 MPa and the dynamic fluid behavior was analyzed for the two geometries mentioned. For the numerical and fluid behavior analysis, a mesh study was conducted to guarantee the independence of the results with the number of discretization cells. The k-ε RNG turbulence model was implemented with treatment of walls, solving in stationary manner the phenomenon occurring within it, given that the temporal evolution is quite rapid. Increased secondary mass flow (extracted) relations with respect to the primary mass flow (injected) were found when the separation communicating the high-pressure zone and the mixture zone diminished. With increased feed pressure of the primary flow, a decrease was found in the secondary mass flow relation with respect to the primary mass flow.Keywords: Compressible Flow, ANSYS, Fluent, Turbulence. ResumenSe presenta la optimización de un eyector de efecto Coandă para aire utilizado ampliamente en la industria mediante la dinámica de fluidos computacional CFD, esta optimización desarrollada en el software ANSYS FLUENT® V16.2. Para el procedimiento de simulación se realizaron dos modelos tridimensionales del eyector comercial ZH30-X185 de la marca SMC® en los cuales se variaron el tamaño de la separación en las paredes de la tobera que comunica la región de alta presión y la zona de mezcla de 0.3 mm y 0.8 mm. Se diseñó un experimento en el cual la presión de alimentación aplicada al eyector toma los valores de 0.20, 0.25 y 0.30 MPa y se analizó el comportamiento fluido dinámico para las dos geometrías anteriormente mencionadas. Para el análisis numérico y fluido dinámico se realizó un estudio de malla para garantizar la independencia de los resultados con el número de celdas de la discretización, se implementó el modelo de turbulencia k-e RNG con tratamiento de paredes y se resolvió de manera estacionaria el fenómeno que ocurre dentro de este, debido a que evolución temporal es muy rápida. Un aumento en las relaciones de flujo másico secundario (extraído) respecto al flujo másico primario (inyectado) fue encontrado cuando se disminuyó la separación que comunica la zona de alta presión y la zona de mezcla. Con el aumento de la presión de alimentación del flujo primario, se encontró una disminución en la relación del flujo másico secundario respecto al flujo másico primario.

Optimisation Analysis of Structural Parameters of an Annular Slot Ejector Based on the Coanda Effect

“…Figure 12 shows that the entrainment ratio gradually decreases as the primary pressure increases from 0.3 MPa to 0.7 MPa. When the mainstream pressure is fixed, the entrainment ratio decreases continuously as the nozzle clearance increases from 0.1 mm to 0.5 mm; a similar trend was obtained elsewhere [30]. It also can be seen that when the primary pressure is 0.3 MPa, the entrainment ratio increases by 42.3% as the nozzle clearance increases from 0.1 mm to 0.15 mm, and the entrainment ratio rises by 85.9% when the nozzle clearance increases from 0.1 mm to 0.5 mm.…”

“…Alexandru et al developed a semiempirical formula for two-dimensional Coanda flow while the curvature of the tangential momentum equation was neglected [16]. Sierra del Rio et al designed a two-ejector model with varying nozzle clearance (0.3 mm and 0.8 mm) to investigate the effect of nozzle clearance on the flow velocity by means of CFD methods [30]; their results showed that the velocity increases with the increase of nozzle clearance. Similar trends were obtained by Lowry et al based on a new Coanda ejector [31].…”