processes Article Optimization Study of Guide Vanes for the Intake Fan-Duct Connection Using CFD Juan Pablo Hurtado 1 , Bryan Villegas 1 , SebastiánPérez 1 and Enrique Acuña 2, *   Citation: Hurtado, J.P.; Villegas, B.; Pérez, S.; Acuña, E. Optimization Study of Guide Vanes for the Intake Fan-Duct Connection Using CFD. Processes 2021, 9, 1555. https:// doi.org/10.3390/pr9091555 Academic Editors: Krzysztof Rogowski, Kristian Etienne Einarsrud, Varun Loomba and Jan Erik Olsen Received: 30 June 2021 Accepted: 23 August 2021 Published: 31 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Departamento de Ingeniería en Minas, Facultad de Ingeniería, Universidad de Santiago, Santiago 9160000, Chile; juan.hurtado@usach.cl (J.P.H.); bryan.villegas@usach.cl (B.V.); sebastian.perez@usach.cl (S.P.) 2 Bharti School of Engineering, Laurentian University, Sudbury, ON P3E 2C6, Canada * Correspondence: enacuna@gmail.com Abstract: The connection between an intake fan and a ventilation shaft must be designed in such a way that it minimizes the energy waste due to singularity losses. As a result, the questions of which radius of curvature to use and if guide vanes have to be included need to be answered. In that case, the variables such as the number, upstream and downstream penetration length, radius of curvature, and width of the vanes, need to be defined. Although this work is oriented to mine ventilation, these questions are usually valid in other engineering applications as well. The objective of this study is to define the previously mentioned variables to determine the optimal design combination for the radius/diameter relationship (r/D). Computational fluid dynamics was used to determine the shock loss factor of seven elbow curvature ratios for a 3 m diameter duct and fan, with and without guide vanes to estimate the best performing configuration and, therefore, to maximize the fan airflow volume. The methodology used consisted of initially developing models in 2D geometries, to optimize the meshing and the CPU use, and studying separately the number of vanes, upstream and downstream penetration, radius of curvature, and width of the vanes for each curvature ratio (r/D). Then, the best-performing variable combinations for each curvature ratio were selected to be simulated and studied with the 3D geometries. The application of the guide vane designs for three- dimensional simulated geometries is presented, first without and then with guide vanes, including the shock loss factors obtained. The methodology and obtained results allowed quantifying the energy savings and to reduce the CFD simulations steps required to optimize the design of the elbow and guide vanes. The results obtained cannot be used with elbows in exhaust fans, because fluid dynamics phenomena are different. Keywords: intake elbow with guide vanes; primary intake; elbow shock losses; elbow design 1. Introduction In underground excavations or tunnels for mining or other applications, fans are commonly installed horizontally on the surface. An elbow connection is necessary to supply the airflow volume underground through the intake raise or shaft. In addition, the layout is usually constrained to a short distance between the fan and the shaft, due to the available footprint or the need to minimize capital expenditure, which produces significant shock losses resulting in energy waste. The elbow generates high turbulence due to boundary layer detachment because of a high-pressure gradient. Therefore, the performance of main fans located on the surface is limited by the elbow pressure loss because there are no more openings to help distribute the airflow in parallel and reduce the pressure loss. This pressure loss directly increases the network resistance experienced by the intake fan. In addition, turbulent flows at a 90 ◦ elbow can cause strong flow separation near the inner wall, which affects the performance of the duct system and can also cause strong flow-induced vibrations and noise [1]. This effect is not observed in fans installed vertically in shafts or ventilation raises. Processes 2021, 9, 1555. https://doi.org/10.3390/pr9091555 https://www.mdpi.com/journal/processes