Vol.2, No 10, 2000 pp. 1449-1451
UDC 532.57(045)
MULTIPLE HOT-WIRE PROBE MEASUREMENTS OF
TURBULENT VELOCITY
AND VORTICITY VECTOR FIELDS
by Petar V. Vukoslavčević and Dragan V. Petrović
Publisher: Montenegrin Academy of Sciences and
Arts, Section of Natural Sciences,
Special Editions, Volume 39, Edition no. 21
The book provides specific information that covers vacant space in voluminous
literature related to hot-wire anemometry. It is focused to the theory
and practical aspects of the application of multiple hot-wire anemometer
probes, specified for measurements of turbulent velocity and vorticity
vector fields, as well as for measurements of dissipation tensor of turbulent
kinetic energy. The importance of such experiments is based on their crucial
role in understanding the mechanism of generating, developing and decay
of the turbulent flows and further advancement of the mathematical models
of turbulence.
The manuscript is organized in eight chapters, with list of 268 references
that include a majority of relevant publications related to development
of this sophisticated measurement method. The book is illustrated with
131 figures. The content is so divided that it corresponds to suggested
logical structure made: "Introduction", "Turbulence and its measurement",
"Constant temperature hot-wire anemo-meters: General principles and signal
analysis", "Measurements of turbulent velocity fields by multiple hot-wire
probes", "Measurements of turbulent vorticity fields by multiple hot-wire
probes", "Operational properties of the vorticity-type and hot-wire probes
for velocity measurements", "Generalized numeric procedure", "Conclusions".
"Introduction" includes a short review of the manuscript and motives
for its writing. The importance of up-to-date contributions in development
of anemometer probes with multiple sensors, as well as the place of some
own authors contributions in this area are also indicated.
"Turbulence and its measurement" and "Constant temperature hot-wire
anemo-meters: General principles and signal analysis" provide fundamental
information that is useful especially for the beginners, since it enables
to comprehend the complex theory presented in further chapters, related
to modern exotic and rare measurements that utilize the multiple hot-wire
probes.
Extremely complex nature of turbulent flows is clearly described in
the second chapter, indicating its stohastics and coherent structure. Accurate
definitions of its basic specific properties enable the beginners to completely
understand subtle differences between the turbulent and other flows and
importance of turbulence research from the theoretical and practical engineering
point of view. Detailed comparison review of the two most important methods
specified for turbulence parameters measurement, hot-wire anemometry and
Laser-Doppler anemometry is also presented here. The conditions and fields
of application for which each of these methods is superior are listed,
showing that these two methods are not only direct competitors, but also
complements: each of them have provided important results in understanding
the complex nature of turbulence in the flows in which the specific method
is superior.
The basic theoretical principles of hot-wire anemometer, primarily
related the foundations of hot-wire anemometry in its standard and classic
applications (i.e. related to the probes possessing one or two sensors),
are also explained here. The sensor cooling mechanism (i.e. relations between
the voltage drop along hot-wire and the instantaneous fluid velocity vector,
basic electronic schemes and principles of primary signal interpretation
procedures are presented. Simultaneously, all limitations of measurements,
based on application of simple probes possessing one or two hot wires,
are indicated, providing the arguments for writing the further text. Presented
information is very useful from the practical point of view, because it
can be used as some kind of "instruction manual" for application of standard
commercial hot-wire anemometers, a necessary step in reaching more complex
measurement techniques based on the multiple hot-wire probes.
The fourth chapter, entitled "Measurements of turbulent velocity fields
by multiple hot-wire probes", entrances the central area of the book, related
to the theory and practice of using the multiple sensor probes specified
for measurement of instantaneous turbulent velocity vector components,
their higher-order moments and gradients. The four-wire probe is chosen
for the central theme, because it represents the basic element of all later
discussed hot-wire probes. The design and manufacturing of the four-wire
probes are explained in detail, as well as the theoretical foundations
of their application, including the influence of probe configurations and
their dimensions on the measurement accuracy. Although these probes provide
the possibility of streamwise vorticity measurement, this chapter is primarily
focused to velocity field measurements. The problem of estimating the uniqueness
range of hot-wires response equations and methods for its enlarging are
discussed in detail. The design and performances of own probe configuration
with eight wires, based on two quadruple probes are explained also. In
this chapter, researchers who wish to design their own probes for specific
purposes can find a detailed guide and recommendations, which will make
easier the probe manufacturing and optimization of their dimensions and
configuration.
The next three chapters, the central part of the monograph, present
primarily own original studies and experience in designing, testing and
using the multiple hot-wire probes. The chapter "Measurements of turbulent
vorticity fields by multiple hot-wire probes" reviews updated information
on the theory and practice of designing, manufacturing and using the vorticity
probes with nine and twelve sensors. The latest results of comparison testing
the nine-wire and twelve-sensor probes are presented, showing clear advantages
of the latter: larger uniqueness range and higher measurement accuracy.
The importance of knowing and accurate measurement of the components of
vorticity vector and turbulent kinetic energy dissipation for better recognizing
the nature of turbulence is explained in detail. Here is also analyzed
the temporal and spatial measuring resolution in the whole range of scales
of turbulent vortex structures, simultaneously discussing the optimal number
of sensors and the probe configuration and dimensions.
The sixth chapter "Operational properties of the vorticity-type and
hot-wire probes for velocity measurements", presents a unique detailed
analysis of measuring accuracy and possible enhancing of the operational
properties of multiple sensor probes. The influence of neglecting the components
of fluid velocity vector and their gradients over hot-wire probe sensing
volume on the measurement accuracy of turbulent velocity field in is discussed
in detail. Possible ways for estimating the optimal probe parameters and
optimal time and frequency of acquiring hot-wire anemometer output voltages
are also presented. On the base of own comparison results of measuring
turbulent velocity field mean statistical parameters by different probe
configurations, authors showed the necessity of using the twelve-wire probes
in three-dimensional flows of higher turbulence level.
In the voluminous chapter, entitled "Generalized numeric procedure",
physical and mathematical background of calibration and signal interpretation
algorithms for the probes with two, four and twelve hot-wires are presented.
Detailed information, provided here, represents a unique useful guide for
the researchers who intend to make an own code for calibration constants
evaluation and hot-wire probes signals interpretation.
"Conclusions" are a short review of the most important conclusions,
showing that presented results of authors in the area of hot-wire anemometry
represent the logical continuation of extensive investigations of many
researches worldwide during many years, showing their belonging to the
world scientific trends and community.
Altogether, this monograph represents a valuable and unique scientific
contribution, originally imagined and even more originally written. It
differs in many elements from the rich available world literature in this
area. As such, the book is an important courageous contribution that will
be accepted with interest among scientific community. The special usefulness
of the monograph is in its practical applicability for future workers in
the complex area of turbulence structure investigation.
Prof. Dr. Simeon Oka, scientific adviser
Belgrade Institute Vinča, Belgrade
