FANS : aerodynamic design - structural noise reduction - optimization

This textbook combines in a unique concept the design and construction of radial and axial fans with the problem of noise generation as well as its mitigation already in the fan development stage. The aim is to describe selected, easily applicable methods of aerodynamic design and noise prediction and to demonstrate their physical principles. Exercises with solutions facilitate understanding. The completely revised and expanded edition now also includes guidance on selecting fans for a given task, simulation-based optimization methods for fan design, and psychoacoustic methods that can be used to measure the quality of fan noise. This book is a translation of the original German 4 th edition Ventilatoren by Thomas Carolus, published by Springer Fachmedien Wiesbaden GmbH, part of Springer Nature in 2020. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com). A subsequent human revision was done primarily in terms of content, so that the book will read stylistically differently from a conventional translation. Springer Nature works continuously to further the development of tools for the production of books and on the related technologies to support the authors. Preface Acknowledgements Contents List of Symbols (Selection) Subscripts Subscripts Abbreviations 1: Basics 1.1 Fan Performance Parameters 1.2 Selection of the Fan: Demand of the Plant 1.3 Aerodynamic Performance Characteristics 1.4 Non-dimensional Parameters, Model Laws, Types of Fans 1.4.1 Non-dimensional Parameters 1.4.2 Model Laws 1.4.3 Scale-Up Methods 1.4.4 Systematics of Fan Types: The Cordier-Diagram 1.5 Practice Problems 1.5.1 Pressure Rise Requirement of a Plant and Fan Specification 1.5.2 Selection of the Type of Fan 1.5.3 From Model- to Full-Scale References 2: Blade Performance Parameters, Cascades of Blades, Kinematics, Losses and Efficiencies 2.1 Blade Work, Blade Volume Flow Rate 2.2 Flow Kinematics (Velocity Triangles) 2.2.1 Cascade of Radial Blades 2.2.2 Cascade of Axial Blades 2.3 Losses and Efficiencies 2.3.1 Losses in the Impeller and Efficiencies 2.3.2 Losses in the Casing and Guide Vanes, Efficiencies References 3: Design of Centrifugal Fans 3.1 Blade Design 3.1.1 Slip of Flow 3.1.2 The Slip Factor 3.1.3 Selection of the Number of Blades 3.1.4 Blockage of the Inlet and Outlet Due to the Finite Thickness of the Blade 3.1.5 Summary: Blade Design for Centrifugal Impellers 3.1.6 Further Empirical Geometry Parameters of the Centrifugal Impeller 3.2 Layout of a Volute Casing 3.2.1 One-Dimensional Streamline Theory 3.2.2 Further Empirical Geometrical Parameters of the Simple Volute Casing 3.3 Practice Problems 3.3.1 Design of a Centrifugal Fan Impeller 3.3.2 Design of a Volute References 4: Design of Axial Fans 4.1 Flow Kinematics in the Axial Impeller: Radial Equilibrium 4.1.1 Isoenergetic Loading Distribution 4.1.2 Radius-Dependent Loading Distribution 4.1.3 Summary of Swirl Distributions 4.2 Segmentation 4.3 The Blade Element Momentum (BEM) Method for Low-Pressure Axial Fans 4.3.1 Derivation of the Key Equation 4.3.2 Summary: Blade Design for Low-Solidity Axial Impellers with the BEM Method 4.3.3 Blade Skew 4.4 The Lieblein Method for High-Pressure Axial Fans 4.4.1 Blade Element Inlet Angle 4.4.2 Blade Exit Angle 4.4.3 Camber and Mean Line 4.4.4 Summary: Blade Design for High-Solidity Axial Impellers 4.5 Design Criteria 4.5.1 De Haller-Criterion 4.5.2 Criterion of Strscheletzky 4.5.3 Diffusion Coefficient According to Lieblein 4.5.4 Further Limitations 4.6 Practice Problems 4.6.1 Design of a Low-Pressure Axial Fan 4.6.2 Design of High-Pressure Axial Fan Stage References Further Reading 5: Sound Generation and Propagation 5.1 The Mechanisms of Sound Generation: An Overview 5.2 Rotating Pressure Fields of Axial Fans 5.2.1 The Rotating Pressure Field of an Isolated Impeller 5.2.2 Rotor-Stator Interaction 5.3 Flow-Induced Sound from Lift-Generating Surfaces 5.4 Sound Propagation 5.4.1 Radiation into the Free Field 5.4.2 Sound Propagation in Ducts: Duct Modes 5.4.3 Excitation of Duct Modes by a Fan 5.5 Significance of Sound Sources and Examples 5.5.1 Rotor-Stator Interaction 5.5.2 Turbulent Inflow, Stall 5.5.3 Vortex Shedding 5.5.4 Tip Clearance Noise 5.6 Practice Problems References 6: Sound Prediction Methods 6.1 Overview 6.2 Class I Sound Prediction Methods 6.2.1 Formula of Madison 6.2.2 Regenscheit ́s Approach 6.2.3 Estimation of the Octave Band Sound Power Level 6.3 Class II Sound Prediction Methods 6.3.1 The Sharland Method 6.3.2 Spectral Distribution 6.3.3 Duct Model 6.3.4 Summary and Example 6.4 Practice Problems 6.4.1 Acoustic Model Law 6.4.2 Fan Acoustic Power References Further Reading Sound in Turbomachinery in General Acoustic Model Laws for Fans Inflow Turbulence Trailing Edge Sound 7: Psychoacoustic Assessment of Fan Noise 7.1 Introduction 7.2 Perception of Annoyance and Quality of Fan Sound 7.3 Two Psychoacoustic Metrics for Fan Noise 7.4 Examples References 8: Design Features of Noise Reduced Fans 8.1 General Measures 8.1.1 Reduction of the Circumferential Speed 8.1.2 Increasing the Spacing Between Stationary and Rotating Components 8.1.3 Phase Shift of the Interaction Between Stationary and Rotating Components 8.1.4 Uneven Blade Spacing 8.1.5 Wavy Leading Edge and Serrated Trailing Edge 8.1.6 Optimum Inlet Geometry and Turbulence Control Screen 8.2 Further Special Measures for Centrifugal Fans 8.2.1 Meridional Contour of Shroud 8.2.2 Suppression of Resonance 8.3 Further Special Measures for Axial Fans 8.3.1 Tuning the Number of Blades (Mode Propagation) 8.3.2 Skewed Blades 8.3.3 Influencing the Tip Gap Flow References 9: Numerical and Experimental Methods 9.1 Numerical Flow Field Simulation 9.1.1 Overview of CFD Methods 9.1.2 Computational Domain and Numerical Grid 9.1.3 Boundary and Initial Conditions 9.1.4 The Rotor-Stator Problem 9.1.5 Control Parameters, Convergence, Residuals and Termination of Iteration 9.1.6 Post Processing 9.1.7 Validation and Verification 9.1.8 Example: Axial Fan 9.2 Experimental Methods 9.2.1 Fan Test Rigs 9.2.2 Measurement of Flow Field Quantities: Measuring Probes 9.2.3 Measurement of Acoustic Quantities 9.3 Optimization 9.3.1 Optimization Procedures 9.3.2 Example: Optimization of an Axial Fan 9.3.3 Example: Centrifugal Fan Impellers with Maximum Total-to-Static Efficiency References Further Reading 10: Appendix 10.1 Effective Pressure Rise 10.1.1 Centrifugal Impeller 10.1.2 Axial Impeller 10.1.3 Axial Impeller with Outlet Guide Vanes and Diffuser 10.2 Airfoil Sections 10.2.1 Isolated Airfoil Section in Unbounded Flow 10.2.2 Airfoil Families 10.2.3 Airfoil Sections in a Cascade 10.3 Some Basics of Acoustics 10.4 Tables 10.5 Lieblein Design Diagrams References 11: Answers to Practice Problems 11.1 Answer to Problem 1.5.1: Pressure Rise Requirement of a Plant and Fan Specification 11.2 Answer to Problem 1.5.2: Selection of the Type of Fan 11.3 Answer to Problem 1.5.3: From Model- to Full-Scale 11.4 Answer to Problem 3.3.1: Design of a Centrifugal Fan Impeller 11.5 Answer to Problem 3.3.2: Design of a Volute 11.6 Answer to Problem 4.6.1: Design of Low-Pressure Axial Fan 11.7 Answer to Problem 4.6.2: Design of High-Pressure Axial Fan Stage 11.8 Answer to Problem 5.6: Axial Fan - Acoustic Modes 11.9 Answer to Problem 6.4.1: Acoustic Model Law 11.10 Answer to Problem 6.4.2: Fan Acoustic Power References Index Fans In a unique approach, this textbook combines the design and construction of centrifugal and axial fans with the problem of their noise generation and its mitigation. Easily applicable methods of fan selection, aerodynamic fan design, and fan noise prediction are compiled, including most of the underlying physical principles. Other features of this book include introductions to numerical and experimental methods, simulation-based optimization techniques for fan design, and psychoacoustic methods for evaluating fan noise. Numerous practical problems illustrate and reinforce the ideas and concepts. Content Fan performance parameters, demand of a plant and fan selection, fan performance characteristics, model laws, flow kinematics, efficiencies – Design methods for centrifugal and axial fans – Mechanisms of fan sound generation, methods for fan sound prediction – Psychoacoustic evaluation of fan noise – Design features of noise reduced fans – Computational fluid dynamics, fan test rigs, simulation-based optimization – Practice problems and solutions. Target group Students of mechanical engineering at colleges and universities Engineers in the industrial fan manufacturing industry, planning engineers for heating, ventilation air conditioning systems and in equipment and plant engineering Author Prof. Dr.-Ing. Thomas Carolus taught fluid mechanics at the Department of Mechanical Engineering at the University of Siegen, Germany, with a focus on fluid machinery. This book is a translation of the original German 4th edition Ventilatoren by Thomas Carolus, published by Springer Fachmedien Wiesbaden GmbH, part of Springer Nature in 2020. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com), but with a subsequent human revision in terms of content. Springer Nature works continuously to further develop tools for the production of books and on the related technologies to support the authors