American Society of Mechanical Engineers

Oscillating-water-column wave energy converters and air turbines: A review

The subject of this monograph is the fluid dynamics of liquid turbomachines, particularly pumps. Rather than attempt a general treatise on turbomachines, we shall focus attention on those special problems and design issues associated with the flow of liquid through a rotating machine. There are two characteristics of a liquid that lead to these special problems, and cause a significantly different set of concerns than would occur in, say, a gas turbine. These are the potential for cavitation and the high density of liquids that enhances the possibility of damaging unsteady flows and forces.

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Hydrodynamics of Pumps

Power density of power electronic converters in different applications has roughly doubled every 10 years since 1970. Behind this trajectory was the continuous advancement of power semiconductor device technology allowing an increase of converter switching frequencies by a factor of 10 every decade. However, today's cooling concepts, and passive components and wire bond interconnection technologies could be major barriers for a continuation of this trend. For identifying and quantifying such technological barriers this paper investigates the volume of the cooling system and of the main passive components for the basic forms of power electronics energy conversion in dependency of the switching frequency and determines switching frequencies minimizing the total volume. The analysis is for 5 kW rated output power, high performance air cooling, advanced power semiconductors, and single systems in all cases. A power density limit of 28 kW/dm3@300 kHz is calculated for an isolated DC-DC converter considering only transformer, output inductor and heat sink volume. For single-phase AC-DC conversion a general limit of 35 kW/dm3 results from the DC link capacitor required for buffering the power fluctuating with twice the mains frequency. For a three-phase unity power factor PWM rectifier the limit is 45 kW/dm3@810 kHz just taking into account EMI filter and cooling system. For the sparse matrix converter the limiting components are the input EMI filter and the common mode output inductor; the power density limit is 71 kW/dm3@50 kHz when not considering the cooling system. The calculated power density limits highlight the major importance of broadening the scope of research in power electronics from traditional areas like converter topologies, and modulation and control concepts to cooling systems, high frequency electromagnetics, interconnection technology, multi-functional integration, packaging and multi-domain modeling and simulation to ensure further advancement of the field along the power density trajectory.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/IEEJ_PowerDensity_Paper_FinalRevised_03.pdf

PWM Converter Power Density Barriers

Physicists are very familiar with forced and parametric resonance, but usually not with self-oscillation, a property of certain dynamical systems that gives rise to a great variety of vibrations, both useful and destructive In a self-oscillator, the driving force is controlled by the oscillation itself so that it acts in phase with the velocity, causing a negative damping that feeds energy into the vibration: no external rate needs to be adjusted to the resonant frequency The famous collapse of the Tacoma Narrows bridge in 1940, often attributed by introductory physics texts to forced resonance, was actually a self-oscillation, as was the swaying of the London Millennium Footbridge in 2000 Clocks are self-oscillators, as are bowed and wind musical instruments The heart is a "relaxation oscillator," ie, a non-sinusoidal self-oscillator whose period is determined by sudden, nonlinear switching at thresholds We review the general criterion that determines whether a linear system can self-oscillate We then describe the limiting cycles of the simplest nonlinear self-oscillators, as well as the ability of two or more coupled self-oscillators to become spontaneously synchronized ("entrained") We characterize the operation of motors as self-oscillation and prove a theorem about their limit efficiency, of which Carnot's theorem for heat engines appears as a special case We briefly discuss how self-oscillation applies to servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business cycle, among other applications Our emphasis throughout is on the energetics of self-oscillation, often neglected by the literature on nonlinear dynamical systems

Self-oscillation

Turbomachinery is a challenging and diverse field, with applications for professionals and students in many subsets of the mechanical engineering discipline, including fluid mechanics, combustion and heat transfer, dynamics and vibrations, as well as structural mechanics and materials engineering. Originally published more than 40 years ago, Fluid Mechanics and Thermodynamics of Turbomachinery is the leading turbomachinery textbook. Used as a core text in senior undergraduate and graduate level courses this book will also appeal to professional engineers in the aerospace, global power, oil & gas and other industries who are involved in the design and operation of turbomachines. For this new edition, author S. Larry Dixon is joined by Cesare Hall from the University of Cambridge, whose diverse background of teaching, research and work experience in the area of turbomachines is well suited to the task of reorganizing and updating this classic text. NEW AND KEY FEATURES * Provides the most comprehensive coverage of the fundamentals of turbomachinery of any text in the field* Content has been reorganized to more closely match how instructors currently teach the course* Coverage of fluid mechanics and thermodynamics, the basis on which good turbomachine performance depends, has been moved to the front of the book* Includes new design studies of several turbomachines, applying the theories developed in the book* Figures have been updated, along with new photos added, to better illustrate the topics presented* Includes new examples and additional end-of-chapter exercises

Fluid mechanics, thermodynamics of turbomachinery

Keywords: turbomachines ; ecoulement ; similitude ; rendement Reference Record created on 2005-11-18, modified on 2016-08-08

Thermodynamics of Turbomachinery

The design and performance prediction of axial flow compressors and turbines has been based upon the measurements of the flow-through two-dimensional cascades of blades. For cascade analysis, the flow across individual blade rows is treated as two-dimensional and steady. This approach is appropriate for many compressor and turbine designs and the derived flow characteristics obtained from cascade tests have usually been found to be satisfactory, although laborious to collect. It is most important that the flow across the central region of the cascade blades is a good approximation to two-dimensional flow and that the flow repeats across several blade pitches. This effect could be achieved by employing a large number of long blades, but then an excessive amount of power would be required to operate the tunnel. A cascade blade profile can be conceived as a curved camber line upon which a profile thickness distribution is symmetrically superimposed. Cascade flow characteristics such as streamtube thickness variation, cascade performance parameters, and blade surface velocity distributions are discussed in the chapter. This also includes discussion on the compressor cascade performance, turbine cascade performance, and the analysis of cascade.

Two-Dimensional Cascades

The chapter discusses the concept of a radial flow turbine that is used for producing hydraulic power. It discusses mainly two types of radial flow turbines—the inward flow radial flow (IFR) and outward flow gas turbines. The IFR turbine covers tremendous ranges of power, rates of mass flow, and rotational speeds, from very large outwards turbines used in hydroelectric power for the generation of hundreds of megawatts down to tiny closed cycle gas turbines for the space power generation of a few kilowatts. The IFR gas turbine continues to be used extensively for powering automotive turbo charges, aircraft auxiliary power units, and expansion units in gas liquefaction. Over a limited range of specific speed, IFR turbines provide efficiency about equal to that of the best axial-flow turbines. The significant advantages offered by the IFR turbine compared with the axial-flow turbine are the greater amount of work that can be obtained per stage, the ease of manufacture, and its superior ruggedness. Different types of inward turbines are also discussed in this chapter, along with the optimum design selection of IFR turbines including factors such as nozzle blade row boundary layers, rotor passage boundary layers, disc wind age, and kinetic energy loss at exit.

Radial-Flow Gas Turbines

This chapter introduces the book on fluid mechanics and the thermodynamics of turbomachines. The book examines, through the laws of fluid mechanics and thermodynamics, the means by which the energy transfer is achieved in the chief types of turbomachines, together with the differing behavior of individual types in their operations. The turbomachines are devices in which energy is transferred continuously flowing fluid by the dynamic action of one or more moving blade rows. Two main categories of turbomachines are identified—those that absorb power to increase the fluid pressure or head (ducted and unducted fans, compressors, and pumps) and those that produce power by expanding fluid to a lower pressure or head (wind, hydraulic, steam, and gas turbines). Methods of analyzing the flow processes differ depending upon the geometrical configuration of the machine. The most fundamental and valuable principles in fluid mechanics is Newton's second law of motion. The momentum equation relates the sum of the external forces acting on a fluid element to its acceleration, or to the rate of change of momentum in the direction of the resultant external force. The chapter presents the basic physical laws of fluid mechanics and thermodynamics, developing them into a form suitable for the study of turbomachines such as the continuity of flow equation, the first law of thermodynamics and the steady flow energy equation, the momentum equation, and the second law of thermodynamics. The energy and entropy equations are introduced in the chapter, along with all-important Euler work equation, which applies to all turbomachines. It also presents important efficiencies such as efficiency of turbines, steam and gas turbines, hydraulic turbines, and compressors and pumps.

S.L. Dixon

Papers

Fluid mechanics, thermodynamics of turbomachinery

Thermodynamics of Turbomachinery

Two-Dimensional Cascades

Radial-Flow Gas Turbines

Introduction: Basic Principles