Turbomachines By B U Pai Pdf Download
Lorean Hoefert
These two types of machines are governed by the same basic relationships including Newton's second Law of Motion and Euler's pump and turbine equation for compressible fluids. Centrifugal pumps are also turbomachines that transfer energy from a rotor to a fluid, usually a liquid, while turbines and compressors usually work with a gas.[1]
The first turbomachines could be identified as water wheels, which appeared between the 3rd and 1st centuries BCE in the Mediterranean region. These were used throughout the medieval period and began the first Industrial Revolution. When steam power started to be used, as the first power source driven by the combustion of a fuel rather than renewable natural power sources, this was as reciprocating engines. Primitive turbines and conceptual designs for them, such as the smoke jack, appeared intermittently but the temperatures and pressures required for a practically efficient turbine exceeded the manufacturing technology of the time. The first patent for gas turbines were filed in 1791 by John Barber. Practical hydroelectric water turbines and steam turbines did not appear until the 1880s. Gas turbines appeared in the 1930s.
In general, the two kinds of turbomachines encountered in practice are open and closed turbomachines. Open machines such as propellers, windmills, and unshrouded fans act on an infinite extent of fluid, whereas closed machines operate on a finite quantity of fluid as it passes through a housing or casing.[2]
In contrast to positive displacement machines (particularly of the reciprocating type which are low speed machines based on the mechanical and volumetric efficiency considerations), the majority of turbomachines run at comparatively higher speeds without any mechanical problems and volumetric efficiency close to one hundred percent.[6]
Axial flow turbomachines - When the path of the through-flow is wholly or mainly parallel to the axis of rotation, the device is termed an axial flow turbomachine.[8] The radial component of the fluid velocity is negligible. Since there is no change in the direction of the fluid, several axial stages can be used to increase power output.
Radial flow turbomachines - When the path of the throughflow is wholly or mainly in a plane perpendicular to the rotation axis, the device is termed a radial flow turbomachine.[8] Therefore, the change of radius between the entry and the exit is finite. A radial turbomachine can be inward or outward flow type depending on the purpose that needs to be served. The outward flow type increases the energy level of the fluid and vice versa. Due to continuous change in direction, several radial stages are generally not used.
Newton's second law describes the transfer of energy. Impulse turbomachines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blading on the rotor.
Turbochargers - Turbochargers are one of the most popular turbomachines. They are used mainly for adding power to engines by adding more air. It combines both forms of turbomachines. Exhaust gases from the engine spin a bladed wheel, much like a turbine. That wheel then spins another bladed wheel, sucking and compressing outside air into the engine.
Air compressors - Air compressors are another very popular turbomachine. They work on the principle of compression by sucking in and compressing air into a holding tank. Air compressors are one of the most basic turbomachines.
Many types of dynamic continuous flow turbomachinery exist. Below is a partial list of these types. What is notable about these turbomachines is that the same fundamentals apply to all. Certainly there are significant differences between these machines and between the types of analysis that are typically applied to specific cases. This does not negate the fact that they are unified by the same underlying physics of fluid dynamics, gas dynamics, aerodynamics, hydrodynamics, and thermodynamics.
This book explores the working principles of all kinds of turbomachines. The same theoretical framework is used to analyse the different machine types. Fundamentals are first presented and theoretical concepts are then elaborated for particular machine types, starting with the simplest ones.For each machine type, the author strikes a balance between building basic understanding and exploring knowledge of practical aspects. Readers are invited through challenging exercises to consider how the theory applies to particular cases and how it can be generalised.
The book is primarily meant as a course book. It teaches fundamentals and explores applications. It will appeal to senior undergraduate and graduate students in mechanical engineering and to professional engineers seeking to understand the operation of turbomachines. Readers will gain a fundamental understanding of turbomachines. They will also be able to make a reasoned choice of turbomachine for a particular application and to understand its operation. Basic design of the simplest turbomachines as a centrifugal fan, an axial steam turbine or a centrifugal pump, is also possible using the topics covered in the book.
Erik Dick was born on December 10, 1950 in Torhout, Belgium. He obtained a M.Sc. in electromechanical engineering from Ghent University in 1973 and a Ph.D. in computational fluid dynamics in 1980. From 1973 he worked as researcher and became full professor of mechanical engineering at Ghent University in 1995, where he teaches turbomachines and computational fluid dynamics. His area of research is computational methods and turbulence and transition models for flow problems in mechanical engineering. He is author or co-author of about 125 papers in international scientific journals and about 250 papers at international conferences. He is the recipient of the 1990 Iwan Akerman award for fluid machinery of the Belgian National Science Foundation.
A turbomachine is basically a rotating blade or a set of rotating blades which in some cases utilizes the energy of the working fluid and in other cases imparts energy to it. Turbomachines are mainly divided into three ways i.e. on the basis of velocity vector of incoming flow (Axial, radial and mixed), on the basis of amount of fluid flow (open and closed), on the basis of utilize the energy (power consuming and power producing). There we will discuss on the third part of turbomachines i.e. on the basis of power consuming or power producing. A turbomachine works on either a high energy fluid or low energy fluid which is known as the primary fluid. Through the years many developments have been made to increase the efficiency of the machines to keep pace with the increasing population and the development of new technologies. In many Turbomachines these requirements are met by introduction of a secondary fluid at specific places or parts of the turbomachine. The secondary fluid can be different from the primary fluid or it can be the same also. There are many methods which utilize the properties of the secondary fluid to increase the performance of the turbomachine. Some methods are in widespread use while others are might be used in future. Some of the examples of methods of injecting secondary fluid are: water injection in jet engines to suppress noise and thus decrease the vibroacoustic stresses. Film cooling technique which injects cold air or steam on gas turbine parts to increase their working life which allows higher firing temperatures and thus increases efficiency. In compressors water is used to increase humidity which helps to increase the efficiency of a hydrogen cell. Apart from all these examples there are so many other applications of fluid injection in turbomachines which are like Air in hydro machines, Air in gas turbines, Air in pumps, Air in marine hydrokinetic turbine, Steam injection in gas turbines, Water injection in jet engines.
Flow induced vibration in turbomachine blade rows is a coupled fluid-structure problem. Thus, instead of utilizing separate fluid and structural models, a coupled interacting fluid-structures analysis is needed. This research addresses this need by application of the new finite element code TAM-ALE3D that solves the three-dimensional unsteady Euler equations in a multi-stage turbomachine environment. The TAM-ALE3D code is derived from the ALE3D code of Lawrence Livermore National Laboratories, and includes algorithms required to model turbomachine geometry. Added features include partially non-reflecting inflow/outflow boundary conditions, and parallel algorithms that allow multiple blade rows to be modeled simultaneously on parallel computer architectures. TAM-ALE3D predictions of the rotor-generated upstream-traveling potential field within the inlet guide vane (IGV) row of the Purdue Transonic Compressor Facility compare well to experimental data. Fluid-structure interaction is first demonstrated by modeling both the isolated rotor flow field and rotor blade, with the aerodynamic damping on the blades quantified through a simulated impact hammer test. Fluid-structure interaction is further demonstrated in a multi-stage environment by simultaneous modeling of the IGV material and flow field, yielding the stresses within the IGV due to excitation from the downstream rotor potential field. The results show the TAMALE3D model not only captures important aerodynamic phenomena within multi-stage turbomachines, but also captures full fluid-structure interaction effects and predicts internal blading stresses.
The present concerns have been primarily with applications to flows of liquids in turbomachines rather than gases. Each medium has its own special problems in addition to the common basis in fluid mechanics. Liquid flows in particular are subject to cavitation when the pressure falls below the vapor pressure. Cavitation is a major element in many applications of naval hydrodynamics. Here the 'turbomachine' is the propulsion system and cavitation on the components of this system, primarily the rotor or propeller, may cause intense noise, if the extent of cavitation is small, significant material erosion if there is a somewhat larger amount of cavitation, or a major performance change (loss of thrust, efficiency, etc.) when there is a large extent of cavitation. The establishment of conditions for the onset of cavitation is then an important feature in almost all naval hydrodynamic applications. Just this particular problem has been the source of much recent effort in cavitation inception research and has been a feature of some of the present work herein.
aa06259810