Handbook Of Flow Visualization

Wen Jei Yang

• Éditeur: Routledge
• Année: 2018
• ISBN:
  9781351442602
• Édition: 2
• Sujet: Technology & Engineering
• Sous-sujet: Mechanical Engineering

With contributions from some of the world's leading experts, the second edition of this classic reference compiles all major techniques of flow visualization and demonstrates their applications in all fields of science and technology. A new chapter has been added that covers flow visualization applications in large wide tunnels for airplane and automobile testing. Several important examples of applications are included. A second new chapter details the use of infrared (IR) cameras for detecting and observing the boundary layer transition in industrial wind tunnels and flight testing of commercial transport airplanes. A final new chapter has been added on multiphase flow and pulsed-light velocimetry.

PART
1 Fundamentals

CHAPTER
1 Introduction

Wen-Jei Yang

Fluid flow, heat and mass transfer, and electrical flow deal with the transfer of physical properties such as momentum, energy, mass, and electricity. Called transport phenomena, they can be investigated both by experiment and by theory. Experimental flow study can be performed in the forms of flow measurement and flow visualization, while the theoretical approach includes analysis and computation as shown in Fig. 1. The task of visualization is to make the process of transport phenomena visible. This can be done through experiments or by simulation (theory). Flow visualization is superior to flow measurement in that the physical phenomena in the entire flow field are retrieved. However, because the information obtained is qualitative, the technique has been inherently penalized (Table 1). The advance of computing machines has led flow visualization into a new era of quantifying the flow information, and thus, the fatal shortcoming of the conventional method has been overcome.

TABLE 1 Comparison of Flow Experiments

	Flow Measurement	Flow Visualization
Range	Local	Whole field
Information	Qualitative	Quantitative

For convenience, the methods used in flow visualization are classified as either conventional or computer assisted. The former, referred to as the first-generation method, includes all traditional techniques in use since the time of Leonardo da Vinci (1452–1519). These techniques are classified into four groups in Table 2: wall tracing, tuft, tracer, and optical methods. The applicable flow range for various methods is presented in Fig. 2. One major objective of research in flow visualization is the extension of the flow range in both directions, toward higher as well as lower velocities.

In general, different substances are introduced into the flow field as a contrast medium or as a tracer to distinguish the object to be observed. Very often, the flow field needs to be illuminated in order to achieve the field image of high contrast and resolution. The image is then displayed in an appropriate form. This is the general practice in conventional flow visualization techniques. The image thus obtained provides only qualitative information about the flow field. In the case of computer-assisted flow visualization methods the above-mentioned process, called image formation, is to be followed by digital image processing. This results in better quality images being displayed. The image-acquisition system includes both the conventional flow visualization device and the imaging device, often referred to as machine vision. Recent advances in computational techniques and computer color graphics have contributed to a new era in flow visualization. Results obtained by theory, measurement, and their combination can be displayed, using colors as the parametric variables. The results can also be stored in the computer for reprocessing. Figure 3 summarizes the computer-aided flow visualization techniques, while Table 3 compares the differences between the first- and second-generation methods of flow visualization.

Fig. 1 Methods to study flow of properties.

TABLE 2 Conventional Flow Visualization Methods

Method	Type
Wall tracing	Liquid film
	Sublimation
	Thermosensible paint
	Electrolytic etching
	Soluble chemical fil...