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3653 results in ebooks in fluid mechanics

Page 145 of 183

  • Preface

  • Erian A. Baskharone, Texas A & M University
  • Book:
    Principles of Turbomachinery in Air-Breathing Engines
    Published online:
    05 September 2012
    Print publication:
    31 July 2006, pp xv-xviii

  • Summary

    Beginning with the class-notes version, this book is the outcome of teaching the courses of Principles of Turbomachinery and Aerospace Propulsion in the mechanical and aerospace engineering departments of Texas A&M University. Over a period of fourteen years, the contents were continually altered and upgraded in light of the students' feedback. This has always been insightful, enlightening, and highly constructive.

    The book is intended for junior- and senior-level students in the mechanical and aerospace engineering disciplines, who are taking gas-turbine or propulsion courses. In its details, the text serves the students in two basic ways. First, it refamiliarizes them with specific fundamentals in the fluid mechanics and thermodynamics areas, which are directly relevant to the turbomachinery design and analysis aspects. In doing so, it purposely deviates from such inapplicable subtopics as external (unbound) flows around geometrically standard objects and airframe-wing analogies. Instead, turbomachinery subcomponents are utilized in such a way to impart the element of practicality and highlight the internal-flow nature of the subject at hand. The second book task is to prepare the student for practical design topics by placing him or her in appropriate real-life design settings. In proceeding from the first to the second task, I have made every effort to simplify the essential turbomachinery concepts, without compromising their analytical or design-related values.

    Judging by my experience, two additional groups are served by the book. First, practicing engineers including, but not necessarily limited to, those at the entry level. As an example, the reader in this category will benefit from the practical means of estimating the stage aerodynamic losses.

  • 9 - Axial-Flow Compressors

  • Erian A. Baskharone, Texas A & M University
  • Book:
    Principles of Turbomachinery in Air-Breathing Engines
    Published online:
    05 September 2012
    Print publication:
    31 July 2006, pp 347-397

  • Summary

    Introduction

    The utilization of axial-flow compressors (Fig. 9.1) in gas-turbine engines has been relatively recent. The history of this compressor type began following an era when centrifugal compressors (Fig. 9.2) were dominant. It was later confirmed, on an experimental basis, that axial-flow compressors can run much more efficiently. Earlier attempts to build multistage axial-flow compressors entailed running multistage axial-flow turbines in the reverse direction. As presented in Chapter 4, a compressor-stage reaction in this case will be negative, a situation that has its own performance-degradation effect. Today, carefully designed axial-flow compressor stages can very well have efficiencies in excess of 80%. A good part of this advancement is because of the standardization of thoughtfully devised compressor-cascade blading rules.

    Comparison with Axial-Flow Turbines

    In passing through a reaction-turbine blade row, the flow stream will continually lose static pressure and enthalpy. The result is a corresponding rise in kinetic energy, making the process one of the flow-acceleration type. In axial compressors, by contrast, an unfavorable static pressure gradient prevails under which large-scale losses become more than likely. It is therefore sensible to take greater care in the compressor-blading phase. Another major difference, by reference to Figure 9.3, is that the compressor meridional flow path is geometrically converging as opposed to the typically diverging flow path of a turbine. This is a direct result of the streamwise density rise in this case, as will be discussed later. Referring to Figure 9.4, another difference in this context is a substantially greater blade count compared wth axial-turbine rotors, where the number of blades is typically in the low twenties.

  • 3 - Aerothermodynamics of Turbomachines and Design-Related Topics

  • Erian A. Baskharone, Texas A & M University
  • Book:
    Principles of Turbomachinery in Air-Breathing Engines
    Published online:
    05 September 2012
    Print publication:
    31 July 2006, pp 26-111

  • Summary

    In this chapter, the flow-governing equations (so-called conservation laws) are reviewed, with applications that are purposely turbomachinery-related. Particular emphasis is placed on the total (or stagnation) flow properties. A turbomachinery-adapted Mach number definition is also introduced as a compressibility measure of the flow field. A considerable part of the chapter is devoted to the so-called total relative properties, which, together with the relative velocity, define a legitimate thermophysical state. Different means of gauging the performance of a turbomachine, and the wisdom behind each of them, are discussed. Also explored is the entropy-production principle as a way of assessing the performance of turbomachinery components. The point is stressed that entropy production may indeed be desirable, for it is the only meaningful performance measure that is accumulative (or addable) by its mere definition.

    The flow behavior and loss mechanisms in two unbladed components of gas turbines are also presented. The first is the stator/rotor and interstage gaps in multistage axial-flow turbomachines. The second component is necessarily part of a turboshaft engine. This is the exhaust diffuser downstream from the turbine section. The objective of this component is to convert some of the turbine-exit kinetic energy into a static pressure rise. Note that it is by no means unusual for the turbine-exit static pressure to be less than the ambient magnitude, which is where the exhaust-diffuser role presents itself.

    In terms of the flow-governing equations, two nonvectorial equations will be covered in this chapter. These are the energy- and mass-conservation equations (better known as the First Law of Thermodynamics and the continuity equation, respectively).

  • 5 - Dimensional Analysis, Maps, and Specific Speed

  • Erian A. Baskharone, Texas A & M University
  • Book:
    Principles of Turbomachinery in Air-Breathing Engines
    Published online:
    05 September 2012
    Print publication:
    31 July 2006, pp 172-207

  • Summary

    Introduction

    In this chapter, a turbomachinery-related nondimensional groupings of geometrical dimensions and thermodynamic properties will be derived. These will aid us in many tasks, such as:

  • Investigating the full-size version of a turbomachine by testing (instead) a much smaller version of it (in terms of the total-to-total pressure ratio), an alternative that would require a much smaller torque and shaft speed, particularly in compressors;

  • Alleviating the need for blade cooling in the component test rig of a high-pressure turbine section by reducing (in light of specific rules) the inlet total temperature;

  • Predicting the consequences of the off-design operation by a turbomachine using the so-called turbine and compressor maps;

  • Making a decision, at an early design phase, in regard to the flow path type (axial or radial) of a turbomachine for optimum performance.

    • A good starting point is to outline the so-called similitude principle, beginning with the definition of geometric and dynamic similarities as they pertain to turbomachines.

    Geometrical Similarity

    Two turbomachines are said to be geometrically similar if the corresponding dimensions are proportional to one another. In this case, one turbomachine is referred to as a scaled-up (or scaled-down) version of the other. An obvious (but not silly) case here is the turbomachine and itself.

    Dynamic Similarity

    Two geometrically similar turbomachines are said to be dynamically similar if the velocity vectors at all pairs of corresponding locations are parallel to one another and with proportional magnitudes. In this case, the fluid-exerted forces, at corresponding locations, will be proportional to each other.

  • 2 - Overview of Turbomachinery Nomenclature

  • Erian A. Baskharone, Texas A & M University
  • Book:
    Principles of Turbomachinery in Air-Breathing Engines
    Published online:
    05 September 2012
    Print publication:
    31 July 2006, pp 9-25

  • Summary

    A brief introduction to gas-turbine engines was presented in Chapter 1. A review of the different engines, included in this chapter, reveals that most of these engine components are composed of “lifting” bodies, termed airfoil cascades, some of which are rotating and others stationary. These are all, by necessity, bound by the hub surface and the engine casing (or housing), as shown in Figures. 2.1 through 2.5. As a result, the problem becomes one of the internal-aerodynamics type, as opposed to such traditional external-aerodynamics topics as “wing theory” and others. Referring, in particular, to the turbofan engines in Chapter 1 (e.g., Fig. 1.3), these components may come in the form of ducted fans. These, as well as compressors and turbines, can be categorically lumped under the term “turbomachines.” Being unbound, however, the propeller of a turboprop engine (Fig. 1.2) does not belong to the turbomachinery category.

    The turbomachines just mentioned, however, are no more than a subfamily of a more inclusive category. These only constitute the turbomachines that commonly utilize a compressible working medium, which is totally, or predominantly, air. In fact, a complete list of this compressible-flow subfamily should also include such devices as steam turbines, which may utilize either a dry (superheated) or wet (liquid/vapor) steam mixture with high quality (or dryness factor). However, there exists a separate incompressible-flow turbomachinery classification, where the working medium may be water or, for instance, liquid forms of oxygen or hydrogen, as is the case in the Space Shuttle Main Engine turbopumps. This subcategory also includes powerproducing turbomachines, such as water turbines.

  • 1 - Introduction to Gas-Turbine Engines

  • Erian A. Baskharone, Texas A & M University
  • Book:
    Principles of Turbomachinery in Air-Breathing Engines
    Published online:
    05 September 2012
    Print publication:
    31 July 2006, pp 1-8

  • Summary

    Definition

    A gas turbine engine is a device that is designed to convert the thermal energy of a fuel into some form of useful power, such as mechanical (or shaft) power or a highspeed thrust of a jet. The engine consists, basically, of a gas generator and a power-conversion section, as shown in Figures 1.1 and 1.2.

    As is clear in these figures, the gas generator consists of the compressor, combustor, and turbine sections. In this assembly, the turbine extracts shaft power to at least drive the compressor, which is the case of a turbojet. Typically, in most other applications, the turbine will extract more shaft work by comparison. The excess amount in this case will be transmitted to a ducted fan (turbofan engine) or a propeller (turboprop engine), as seen in Figure 1.2. However, the shaft work may also be utilized in supplying direct shaft work, or producing electricity in the case of a power plant or an auxiliary power unit (Fig. 1.1). The fact, in light of Figures 1.1 through 1.5, is that different types of gas-turbine engines clearly result from adding various inlet and exit components, to the gas generator. An always interesting component in this context is the thrust-augmentation devices known as afterburners in a special class of advanced propulsion systems (Fig. 1.4).

    Gas-turbine engines are exclusively used to power airplanes because of their high power-to-weight ratio. They have also been used for electric-power generation in pipeline-compressor drives, as well as to propel trucks and tanks. In fact, it would be unwise to say that all possible turbomachinery applications have already been explored.

  • 1 - Introduction

  • Carl Wunsch, Massachusetts Institute of Technology
  • Book:
    Discrete Inverse and State Estimation Problems
    Published online:
    28 October 2009
    Print publication:
    29 June 2006, pp 3-18

  • Summary

    The most powerful insights into the behavior of the physical world are obtained when observations are well described by a theoretical framework that is then available for predicting new phenomena or new observations. An example is the observed behavior of radio signals and their extremely accurate description by the Maxwell equations of electromagnetic radiation. Other such examples include planetary motions through Newtonian mechanics, or the movement of the atmosphere and ocean as described by the equations of fluid mechanics, or the propagation of seismic waves as described by the elastic wave equations. To the degree that the theoretical framework supports, and is supported by, the observations one develops sufficient confidence to calculate similar phenomena in previously unexplored domains or to make predictions of future behavior (e.g., the position of the moon in 1000 years, or the climate state of the earth in 100 years).

    Developing a coherent view of the physical world requires some mastery, therefore, of both a framework, and of the meaning and interpretation of real data. Conventional scientific education, at least in the physical sciences, puts a heavy emphasis on learning how to solve appropriate differential and partial differential equations (Maxwell, Schrödinger, Navier—Stokes, etc.). One learns which problems are “well-posed,” how to construct solutions either exactly or approximately, and how to interpret the results.

  • 6 - Applications to steady problems

  • Carl Wunsch, Massachusetts Institute of Technology
  • Book:
    Discrete Inverse and State Estimation Problems
    Published online:
    28 October 2009
    Print publication:
    29 June 2006, pp 279-339

  • Summary

    The focus will now shift away from discussion of estimation methods in a somewhat abstract context, to more specific applications, primarily for large-scale fluid flows, and to the ocean in particular. When the first edition of this book (OCIP) was written, oceanographic uses of the methods described here were still extremely unfamiliar to many, and they retained an aura of controversy. Controversy arose for two reasons: determining the ocean circulation was a classical problem that had been discussed with ideas and methods that had hardly changed in 100 years; the introduction of algebraic and computer methods seemed to many to be an unwelcome alien graft onto an old and familiar problem. Second, some of the results of the use of these methods were so at odds with “what everyone knew,” that those results were rejected out of hand as being obviously wrong – with the methods being assumed flawed.

    In the intervening 25+ years, both the methodology and the inferences drawn have become more familiar and less threatening. This change in outlook permits the present chapter to focus much less on the why and how of such methods in the oceanographic context, and much more on specific examples of how they have been used. Time-dependent problems and methods will be discussed in Chapter 7.

Page 145 of 183