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Über dieses Buch

Smol'yakov and Tkachenko's book is a very thorough and detailed survey of the response of hot wires and related trans­ ducers to a fluctuating flow field. Now that the electronic equipment needed for hot-wire anemometry is so easy to make or cheap to buy, transducer response is the most critical part of the subject - except for the fragility of the sensing element , for which textbooks are no remedy! We hope that this book will be useful to all students and research workers concerned with the theory or practice of these devices or the interpretation of results. Peter Bradshaw Imperial College London v Preface "The importance of experimental data and of experimentally established general properties is often underestimated in the study of turbulence . . . •. The most direct path is to use experimentally established properties as the foundation upon which models explaining these properties can be constructed. " M. D. Millionshchikov Turbulence belongs to a class of physical phenomena that are very frequently encountered in both nature and technology. It is the most common and also the most complicated form of motion of real liquids and gases. It is observed in the oceans, in the atmosphere, and in a very wide range of systems in engineering. The rational design of airplanes, rockets, ships, dams, hydroelectric plant, canals, turbines, ventilators, and many other technological systems must involve the consideration of turbulence.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Statistical Description of Turbulence

Abstract
The most immediate impression of turbulent flow is, probably, that it is an exceedingly complicated, tortuous and chaotic phenomenon. The experimenter equipped with instruments capable of recording the parameters of a turbulent flow will soon conclude that all these parameters fluctuate in an irregular fashion.
A. V. Smol’yakov, V. M. Tkachenko

Chapter 2. Measurement of Turbulent Fluctuations

Abstract
In Chapter One, we were largely concerned with identifying the statistical characteristics of turbulent flows that might be of interest in experimental studies of such flows. In the present chapter, we shall consider how such studies can be carried out.
A. V. Smol’yakov, V. M. Tkachenko

Chapter 3. Transducers of Finite Size in Turbulent Fluctuations

Abstract
We now begin a detailed examination of one of the basic uncertainties in the measured turbulent fluctuation characteristics, namely, that due to the finite size of the sensitive part of the transducer. We recall that most of the methods available for measuring the statistical parameters of particular physical variables in turbulent flows involve as a necessary step the transformation of these variables into an electrical signal. It is precisely this component of the measuring channel, i.e., the converter, that may substantially distort the measured variable. The reason for this lies in the mismatch between the transducer and the object under examination. The point is that the fluctuation field of any turbulent variable contains a set of spatial inhomogenities, the linear dimensions of which lie in a very broad range. This also applies to time intervals characterizing the variation of the turbulent variable at each point in space occupied by the flow. Measurements are free from distortion when the sensitive part of the transducer is infinitesimal and the transducer itself can react instantaneously to changes in the measured variable.
A. V. Smol’yakov, V. M. Tkachenko

Chapter 4. Statistical Models of Turbulent Fields

Abstract
When the correction functions were calculated in the last chapter, for different characteristics of the velocity fluctuation field, the “true” velocity field or, more precisely, its spectral energy tensor, was specified in each case. This transition from the “true” field to the correction function suffers from a logical difficulty, namely, the correction to the measured field variable relies on information about the true distribution of this variable. However, this information is either not available, in which case, the correction cannot be made, or it is available, in which case there is no need for correction. This sequence of events is dictated by the structure of the general relationships in Section 3.1, which enable us to determine the results of measurements if the field is known by not the other way round. The problem facing the experimenter, on the other hand, is the converse: to determine the statistical characteristics of the field acting on the transducer from the measured values of the field. The question is whether it is possible to invert the relationships obtained in Section 3.1. It turns out that this leads to certain fundamental difficulties.
A. V. Smol’yakov, V. M. Tkachenko

Chapter 5. Correction Functions for the Pressure Fluctuation Field

Abstract
In this chapter, we shall use the general results of Chapter Three together with the field models presented in the last chapter to construct correction functions that take into account the effect of the size of the receiving surface of the transducer on the measured spectral characteristics of the turbulent pressure field near a wall. We begin with the correction functions for the power spectrum. The relationship between the size of the receiving surface of a pressure transducer and the size of the smallest eddies in the boundary layer is such that the measured power spectrum is sensitive to the transducer size in a broad frequency range, and the distortion of the spectrum at high frequencies may amount to several orders of magnitude. It is then frequently impossible to use the uncorrected measurements directly. Since the pressure field at each point in space is determined by the velocity field within a certain volume of the fluid (theoretically, in the entire volume of the turbulent fluid), the pressure field is less “rigid” than the velocity field. The measured power spectra and the correction functions are, therefore, often given as functions of the frequency and not of the wavenumber (as in the case of the velocity fluctuations considered in Section 3.4).
A. V. Smol’yakov, V. M. Tkachenko

Backmatter

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