Preface

Chapter 7 **Experimental Study of Internal Flow Noise Measurement by Use of a Suction Type Low Noise Wind Tunnel 147**

Chapter 9 **Statistical Analysis of Wind Tunnel and Atmospheric Boundary**

Adrián Roberto Wittwer, Guilherme Sausen Welter and Acir M.

Chapter 8 **Investigation of Drying Mechanism of Solids Using**

Yoshifumi Yokoi

**VI** Contents

**Wind Tunnel 165** Abdulaziz Almubarak

Loredo-Souza

**Layer Turbulent Flows 197**

Human efforts to conquer flight, land on the moon, go beyond the earth and discover new universes would have been difficult without the development of wind tunnels. The early 18th and 19th century aerodynamists used whirling arm to study various shapes which suf‐ fered from a major fault that the body under investigation was forced to fly in its own un‐ disturbed wake. This has lead to the development of wind tunnels to overcome the problem.

Wind tunnels are essentially test facilities that create undisturbed flow in which test models can be placed and controlled tests conducted to ascertain the subsequent changes on the test models. With rapid developments in electronics and computer technologies, computational fluid dynamics has become an important and cheap tool in the investigation of complex flu‐ id flow fields. It was often opined purely from cost considerations of manufacture, opera‐ tion, maintenance that wind tunnels would soon become extinct and be replaced by the emerging numerical computations and simulations. However, as time has progressed, re‐ searchers are beginning to realise that to conduct meaningful numerical simulations, there is an even greater need to validate their research that requires accurate and high quality data and hence the need for wind tunnel experiments. The wind tunnels are, therefore, upgraded with modern instruments and data acquisition, analysis systems and their overall operations are computerised. These developments have also opened up new possibilities and ushered in novel applications of the wind tunnels for non-aeronautical applications. It is against this backdrop that work on this book was undertaken.

The book is a compilation of works from world experts on subsonic and supersonic wind tunnel designs, applicable to a diverse range of disciplines. The book is organised in two sections of five chapters each. The first section, Section A, comprises of three chapters on various aspects of low speed wind tunnel designs, followed by one chapter on supersonic wind tunnel and the final chapter discusses a method to address unsteadiness effects of fan blade rotation. The second section, Section B, contains five chapters regarding wind tunnel applications across a multitude of engineering fields including civil, mechanical, chemical and environmental engineering.

The first chapter is written by experts collaborating from two academic institutes, namely Polytechnic University of Madrid and Beijing Institute of Technology. The authors give an excellent introduction to the significance of wind tunnels for both aeronautical and non-aer‐ onautical applications. The authors tackle the main issue facing wind tunnel design and con‐ struction of today head on; that is the cost of manufacture and operation without compromising on quality. They describe a method for quick design of low speed and low cost wind tunnels in great details for aeronautical and/or civil applications.

The second chapter further reinforces the design aspects of a closed circuit low speed wind tunnel that is used both for teaching and research activities. The wind tunnel is located at the aerodynamics research laboratory of the University of New South Wales. A major fea‐ ture of this wind tunnel is the availability of the provision of interchangeable cross sections. This second chapter along with the first chapter have been presented with sufficient details and references and would, therefore, be expected to act as valuable guide to future wind tunnel design constructions.

The third chapter, Chapter 3, considers the design of 'portable' wind tunnels as opposed to stationary wind tunnels that were the themes of the previous two chapters. The author of this chapter describes the design of wind tunnel aptly as the 'combination of art, science, and common sense, the last being the most essential'. It is written with great authority by an expert who has designed such wind tunnels for studies to understand the controlling proc‐ esses of aeolian particle movement, assessing the erodibility of natural surfaces subjected to different disturbances, estimating dust emission rates for natural surfaces, investigating the partitioning of chemical and microbiological components of the soil on entrained sediment, and estimating the threshold wind velocity necessary to initiate aeolian particle movement. When properly designed, calibrated, constructed, and operated, this form of wind tunnel can provide very useful information in a relatively short period of time.

The fourth chapter is a slight departure from the subsonic wind tunnel design theme and describes the design features of a supersonic wind tunnel currently in operation at the aer‐ odynamics laboratory of the University of New South Wales. The construction and opera‐ tion of supersonic wind tunnel is quite expensive and complex, and requires a shock free test section. In order to operate supersonic wind tunnel, it is imperative that appropriate gas dynamic facility capable of producing the desired compressed air be available. Materials in this chapter have, therefore, been presented in two parts; the first part describes the design and development of a gas dynamics facility while the second part deals with the superson‐ ic wind tunnel.

The fifth and the final chapter of this section of the book does not deal with the design of the wind tunnel directly, but details a method that addresses the unsteadiness effects emanating from fan blade rotation using what is called the 'Richardson's Annular Effect'. This is an important consideration, since most subsonic wind tunnels are designed with the assump‐ tion that the flow would be steady during operation.

The non-aeronautical applications of wind tunnels form the theme of the second Section of this book.

The first chapter of second Section, called Chapter 6 continues with a further example of ap‐ plication of wind tunnel in civil engineering and building industry. This chapter is written collaboratively by experts who include a practicing structural engineer and several academ‐ ics. In this Chapter, the authors describe wind tunnel tests conducted on a complicated hornshaped membrane roof. In general, there are two types of wind-tunnel test on the membrane roof, namely a test using a rigid model and a test using an elastic model. The test of the rigid model is used to measure the wind pressure around the building. On the other hand, the test of the elastic model can measure the deflection of the membrane surface directly and grasp the behavior of the membrane. This chapter describes how wind tunnel test is used to clarify the various flow features associated with the rigid model for the horn-shaped membrane roof

structure and quantify the wind-force coefficient and fluctuating wind pressure coefficient around membrane under turbulent boundary layer flow condition.

The second chapter further reinforces the design aspects of a closed circuit low speed wind tunnel that is used both for teaching and research activities. The wind tunnel is located at the aerodynamics research laboratory of the University of New South Wales. A major fea‐ ture of this wind tunnel is the availability of the provision of interchangeable cross sections. This second chapter along with the first chapter have been presented with sufficient details and references and would, therefore, be expected to act as valuable guide to future wind

The third chapter, Chapter 3, considers the design of 'portable' wind tunnels as opposed to stationary wind tunnels that were the themes of the previous two chapters. The author of this chapter describes the design of wind tunnel aptly as the 'combination of art, science, and common sense, the last being the most essential'. It is written with great authority by an expert who has designed such wind tunnels for studies to understand the controlling proc‐ esses of aeolian particle movement, assessing the erodibility of natural surfaces subjected to different disturbances, estimating dust emission rates for natural surfaces, investigating the partitioning of chemical and microbiological components of the soil on entrained sediment, and estimating the threshold wind velocity necessary to initiate aeolian particle movement. When properly designed, calibrated, constructed, and operated, this form of wind tunnel

The fourth chapter is a slight departure from the subsonic wind tunnel design theme and describes the design features of a supersonic wind tunnel currently in operation at the aer‐ odynamics laboratory of the University of New South Wales. The construction and opera‐ tion of supersonic wind tunnel is quite expensive and complex, and requires a shock free test section. In order to operate supersonic wind tunnel, it is imperative that appropriate gas dynamic facility capable of producing the desired compressed air be available. Materials in this chapter have, therefore, been presented in two parts; the first part describes the design and development of a gas dynamics facility while the second part deals with the superson‐

The fifth and the final chapter of this section of the book does not deal with the design of the wind tunnel directly, but details a method that addresses the unsteadiness effects emanating from fan blade rotation using what is called the 'Richardson's Annular Effect'. This is an important consideration, since most subsonic wind tunnels are designed with the assump‐

The non-aeronautical applications of wind tunnels form the theme of the second Section of

The first chapter of second Section, called Chapter 6 continues with a further example of ap‐ plication of wind tunnel in civil engineering and building industry. This chapter is written collaboratively by experts who include a practicing structural engineer and several academ‐ ics. In this Chapter, the authors describe wind tunnel tests conducted on a complicated hornshaped membrane roof. In general, there are two types of wind-tunnel test on the membrane roof, namely a test using a rigid model and a test using an elastic model. The test of the rigid model is used to measure the wind pressure around the building. On the other hand, the test of the elastic model can measure the deflection of the membrane surface directly and grasp the behavior of the membrane. This chapter describes how wind tunnel test is used to clarify the various flow features associated with the rigid model for the horn-shaped membrane roof

can provide very useful information in a relatively short period of time.

tion that the flow would be steady during operation.

tunnel design constructions.

VIII Preface

ic wind tunnel.

this book.

In today's world, noise is an important issue of paramount importance. In Chapter 7 a meas‐ urement technique of the fluid-dynamic noise of an internal flow is presented. A suction type low noise wind tunnel was used to obtain measurement of the fluid-dynamic noise made from a circular cylinder placed in the air flow. The study was carried out through bur‐ ial setting of a microphone to the test section equipped with a fibered glass. The results ob‐ tained by this measurement technique were compared with the measurement results obtained from a blow type wind tunnel that showed clearly that usefulness of the technique and one that could be very useful in high to fluid-dynamic noise measurement of the inter‐ nal flow.

Application of wind tunnel in chemical engineering forms the basis of Chapter 8. Drying of solids provides a technical challenge due to the presence of complex interactions between the simultaneous processes of heat and mass transfer, both on the surface and within the structure of the materials being dried. Internal moisture flow can occur by a complex mecha‐ nism depending on the structure of the solid body, moisture content, temperature and pres‐ sure in capillaries and pores. External conditions such as temperature, humidity, pressure, the flow velocity of the drying medium and the area of exposed surface also have a great effect on the mechanisms of drying. The most important variables in any drying process such as air flow, temperature and humidity are usually easy to be controlled inside a wind tunnel. Through a mathematical approach and an experimental work using a wind tunnel, the materials the author brilliantly highlights the role of the boundary layer on the interface behaviour and the drying mechanisms for various materials of a flat plate surface and a sin‐ gle droplet shape. This chapter is another excellent example of versatility of effective wind tunnel application in non-aeronautical field.

The final chapter, Chapter 9, shows how wind tunnel data can be used in wind engineering that require the use of different types of statistical analysis associated to the phenomenology of boundary layer flows. Reduced Scale Models (RSM) obtained in laboratory, for example, attempt to reproduce real atmosphere phenomena like wind loads on buildings and bridges and the transportation of gases and airborne particulates by the mean flow and turbulent mixing. Therefore, the quality of the RSM depends on the proper selection of statistical pa‐ rameters and in the similarity between the laboratory generated flow and the atmospheric flow. Analysis of the fully developed turbulence measurements from the laboratory and the atmospheric boundary layer encompassing a wide range of Reynolds number are presented in this chapter. First, a typical spectral evaluation of a boundary layer simulation is present‐ ed. The authors find that this type of analysis is suitable to verify boundary layer flows at low speed used for dispersion modeling and that time scales for fluctuating process model‐ ing could also be improved by applying this analysis method.

This book is intended to be a valuable addition to students, engineers, scientists, industrial‐ ists, consultants and others by providing greater insights into wind tunnel designs and their enormous research potential not only in aeronautical fields, but also in other non-aeronauti‐ cal disciplines.

It is worth emphasising that all chapters have been prepared by professionals who are ex‐ perts in their respective research fields and the contents reflect the views of the author(s)

#### X Preface

concerned. All chapters included in this book have been subjected to peer-review and are culmination of the interactions of the editor, publisher and authors.

The editor would like to take this opportunity and thank all the authors for their expert con‐ tributions and the publisher for their patience and hard work in producing this book and thereby drawing a successful conclusion of a project of high practical significance.

> **N. A. Ahmed** Head, Aerospace Engineering, School of Mechanical Engineering, University of New South Wales, Sydney, Australia

**Section 1**
