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Optimum Design of Compact, Quiet, and Efficient Ventilation Fans Optimum Design of Compact, Quiet, and Efficient Ventilation Fans Mark Pastor Hurtado Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Mechanical Engineering Ricardo A. Burdisso, Committee Chair Pablo A. Tarazaga William J. Devenport Wing F. Ng Seongim S. Choi December 16th, 2019 Blacksburg, VA Keywords: Multi-element, Tandem, Compact, Fan design Copyright 2019, Mark Pastor Hurtado Optimum Design of Compact, Quiet, and Efficient Ventilation Fans Mark Pastor Hurtado ABSTRACT Axial ventilation fans are used to improve the air quality, remove contaminants, and to control the temperature and humidity in occupied areas. Ventilation fans are one of the most harmful sources of noise due to their close proximity to occupied areas and widespread use. The prolonged exposure to hazardous noise levels can lead to noise- induced hearing loss. Consequently, there is a critical need to reduce noise levels from ventilation fans. Since fan noise scales with the 4-6th power of the fan tip speed, minimizing the fan tip speed and optimizing the duct geometry are effective methods to reduce fan noise. However, there is a tradeoff between reducing fan speed, noise and aerodynamic efficiency. To this end, a new innovative comprehensive optimum design methodology considering both aerodynamic efficiency and noise was formulated and implemented using a multi-objective genetic algorithm. The methodology incorporates a control vortex design approach that results in a spanwise chord and twist distribution of the blades that maximize the volumetric flow rate contribution of the outer radii, i.e. the axial flow velocity increases from the fan hub to the tip. The resulting blade geometry generates a given volumetric flow rate at the minimum fan tip speed. The fan design is complemented by the design of the optimum inlet duct geometry to maximize volumetric flow rate and minimize BL thickness for low noise generation. Good agreement with experimental results validates the design process. The present study also incorporates multi-element airfoils to further increase the aerodynamic characteristics of the fan blades and enable lower fan speeds and noise. Good agreement between experiments and predictions indicate that traditional blade element momentum methods can be implemented in conjunction with multi-element airfoil aerodynamic characteristics with good accuracy. A direct comparison of fans designed with single and multi-element airfoils has shown that fans designed with multi-element airfoils aerodynamically outperform single element airfoil fans. Optimum Design of Compact, Quiet, and Efficient Ventilation Fans Mark Pastor Hurtado GENERAL AUDIENCE ABSTRACT Axial ventilation fans are widely used to improve the air quality, remove contaminants, and to control the temperature and humidity in occupied areas. However, high noise levels from ventilations fans are a harmful source of noise that can lead to irreversible noise- induced hearing loss. Therefore, this work addresses a critical need for quiet and efficient ventilation fans. To this end, a new innovative comprehensive optimum design methodology considering both aerodynamic efficiency and noise was formulated, implemented, and tested. The methodology optimizes the fan geometry to maximize the volumetric flow rate and minimize noise. The fan design is complemented by the design of the optimum inlet duct geometry to increase the volumetric flow rate and minimize BL thickness for low noise generation. Good agreement with experimental results validates the design process. The present study also incorporates multi-element airfoils to further increase the aerodynamic characteristics of the fan blades. A direct comparison of fans designed with single and multi-element airfoils has shown that fans designed with multi- element airfoils aerodynamically outperform single element airfoil fans. Acknowledgements I would like to thank my advisor Dr. Ricardo Burdisso, whose technical insight, encouragement, and support created a wonderful environment in which to grow, professionally, academically, and personally during my graduate studies at Virginia Tech. I would also like to express my gratitude and appreciation to the members of my committee Dr. Pablo Tarazaga, Dr. William Devenport, Dr. Wing Ng, and Dr. Seongim Choi for their input and support. Additionally, I would like to thank my colleagues Sterling McBride, Lucas Spies, Pradosh Pritam Dash, and Daniel Wu from the Vibrations and Acoustics laboratory for their assistance in setting up experiments. I will always cherish their help, friendship and technical insights. Lastly, I would also like to thank the members of the GradSHPE chapter for creating a sense of community in Blacksburg where I could grow personally, academically, and professionally. Special thanks to Anthony Millican, Genesis Alvarez, Javier González-Rocha, Elisa Wasson, John Angarita, Kevin Moreno, Adam Lowery, and Adrian Davila for their insightful conversation and laughter. I dedicate this dissertation to my parents and my fiancé Alyssa Murray, whose continuous and unconditional support have been essential for the completion of this work. Lastly, I would like to thank God for giving me the opportunity to successfully accomplish my academic and professional goals. iv Table of Contents ABSTRACT ................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................ iv TABLE OF CONTENTS ............................................................................................................. v LIST OF FIGURES .................................................................................................................... vii LIST OF TABLES ...................................................................................................................... xii NOMENCLATURE ................................................................................................................... xiii 1 INTRODUCTION AND MOTIVATION ........................................................................... 1 2 LITERATURE REVIEW .................................................................................................... 6 3 AERODYNAMIC AND ACOUSTIC DESIGN TOOLS ................................................ 23 3.3.1 Rotor Self-Noise (RSN).......................................................................................................................... 32 3.3.2 Turbulence Rotor Interaction Noise (TRIN) .......................................................................................... 35 3.3.3 Computation of Total Sound Power Spectrum ..................................................................................... 41 4 FAN DESIGN ...................................................................................................................... 45 4.1.1 Airfoil Selection .................................................................................................................................... 46 4.1.2 Optimum Fan Dimensions and Velocity Profile Design ........................................................................ 52 4.1.3 Blade Geometry ................................................................................................................................... 57 4.1.4 Duct Design .......................................................................................................................................... 59 4.2.1 Tandem Airfoil Design .......................................................................................................................... 67 4.2.2 Multi-element Airfoil Blades Design .................................................................................................... 76 5 EXPERIMENTAL RESULTS AND VALIDATION ...................................................... 81 5.1.1 Experimental Facility ............................................................................................................................ 81 5.1.2 Fan Test Rig .......................................................................................................................................... 81 5.1.3 Instrumentation and Data Processing ................................................................................................. 89 5.2.1 Fan Power Results ................................................................................................................................ 96 5.2.2 Axial Flow Velocity Results ................................................................................................................... 98 5.3.1 Spectral Characteristics...................................................................................................................... 103 v 5.3.2 Noise Source Identification ................................................................................................................ 108 6 MULTI-FAN DESIGN ..................................................................................................... 119 6.2.1 Experimental set up ........................................................................................................................... 122 6.2.2 Aerodynamic Results .........................................................................................................................
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