Chapter 1 INTRODUCTION AND BASIC CONCEPTS
Pletschet, Cliff, Financial Columnist has reference to this Academic Journal, PHwiki organized this Journal Chapter 1 INTRODUCTION AND BASIC CONCEPTS Lecture slides by Mehmet Kanoglu Copyright © The McGraw-Hill Companies, Inc. Permission required as long as reproduction or display. Fluid Mechanics: Fundamentals in addition to Applications 3rd Edition Yunus A. Cengel, John M. Cimbala McGraw-Hill, 2014 Schlieren image showing the thermal plume produced by Professor Cimbala as he welcomes you to the fascinating world of fluid mechanics. Objectives Underst in addition to the basic concepts of Fluid Mechanics. Recognize the various types of fluid flow problems encountered in practice. Model engineering problems in addition to solve them in a systematic manner. Have a working knowledge of accuracy, precision, in addition to significant digits, in addition to recognize the importance of dimensional homogeneity in engineering calculations.
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11 INTRODUCTION Fluid mechanics deals with liquids in addition to gases in motion or at rest. Mechanics: The oldest physical science that deals with both stationary in addition to moving bodies under the influence of as long as ces. Statics: The branch of mechanics that deals with bodies at rest. Dynamics: The branch that deals with bodies in motion. Fluid mechanics: The science that deals with the behavior of fluids at rest (fluid statics) or in motion (fluid dynamics), in addition to the interaction of fluids with solids or other fluids at the boundaries. Fluid dynamics: Fluid mechanics is also referred to as fluid dynamics by considering fluids at rest as a special case of motion with zero velocity. Hydrodynamics: The study of the motion of fluids that can be approximated as incompressible (such as liquids, especially water, in addition to gases at low speeds). Hydraulics: A subcategory of hydrodynamics, which deals with liquid flows in pipes in addition to open channels. Gas dynamics: Deals with the flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds. Aerodynamics: Deals with the flow of gases (especially air) over bodies such as aircraft, rockets, in addition to automobiles at high or low speeds. Meteorology, oceanography, in addition to hydrology: Deal with naturally occurring flows. What is a Fluid Fluid: A substance in the liquid or gas phase. A solid can resist an applied shear stress by de as long as ming. A fluid de as long as ms continuously under the influence of a shear stress, no matter how small. In solids, stress is proportional to strain, but in fluids, stress is proportional to strain rate. When a constant shear as long as ce is applied, a solid eventually stops de as long as ming at some fixed strain angle, whereas a fluid never stops de as long as ming in addition to approaches a constant rate of strain. De as long as mation of a rubber block placed between two parallel plates under the influence of a shear as long as ce. The shear stress shown is that on the rubberan equal but opposite shear stress acts on the upper plate.
Stress: Force per unit area. Normal stress: The normal component of a as long as ce acting on a surface per unit area. Shear stress: The tangential component of a as long as ce acting on a surface per unit area. Pressure: The normal stress in a fluid at rest. Zero shear stress: A fluid at rest is at a state of zero shear stress. When the walls are removed or a liquid container is tilted, a shear develops as the liquid moves to re-establish a horizontal free surface. The normal stress in addition to shear stress at the surface of a fluid element. For fluids at rest, the shear stress is zero in addition to pressure is the only normal stress. Unlike a liquid, a gas does not as long as m a free surface, in addition to it exp in addition to s to fill the entire available space. In a liquid, groups of molecules can move relative to each other, but the volume remains relatively constant because of the strong cohesive as long as ces between the molecules. As a result, a liquid takes the shape of the container it is in, in addition to it as long as ms a free surface in a larger container in a gravitational field. A gas exp in addition to s until it encounters the walls of the container in addition to fills the entire available space. This is because the gas molecules are widely spaced, in addition to the cohesive as long as ces between them are very small. Unlike liquids, a gas in an open container cannot as long as m a free surface. The arrangement of atoms in different phases: (a) molecules are at relatively fixed positions in a solid, (b) groups of molecules move about each other in the liquid phase, in addition to (c) individual molecules move about at r in addition to om in the gas phase. Intermolecular bonds are strongest in solids in addition to weakest in gases. Solid: The molecules in a solid are arranged in a pattern that is repeated throughout. Liquid: In liquids molecules can rotate in addition to translate freely. Gas: In the gas phase, the molecules are far apart from each other, in addition to molecular ordering is nonexistent.
Gas in addition to vapor are often used as synonymous words. Gas: The vapor phase of a substance is customarily called a gas when it is above the critical temperature. Vapor: Usually implies that the current phase is not far from a state of condensation. On a microscopic scale, pressure is determined by the interaction of individual gas molecules. However, we can measure the pressure on a macroscopic scale with a pressure gage. Macroscopic or classical approach: Does not require a knowledge of the behavior of individual molecules in addition to provides a direct in addition to easy way to analyze engineering problems. Microscopic or statistical approach: Based on the average behavior of large groups of individual molecules. Application Areas of Fluid Mechanics Fluid dynamics is used extensively in the design of artificial hearts. Shown here is the Penn State Electric Total Artificial Heart.
12 A BRIEF HISTORY OF FLUID MECHANICS Segment of Pergamon pipeline. Each clay pipe section was 13 to 18 cm in diameter. A mine hoist powered by a reversible water wheel. Osborne Reynolds original apparatus as long as demonstrating the onset of turbulence in pipes, being operated by John Lienhard at the University of Manchester in 1975.
The Wright brothers take flight at Kitty Hawk. Old in addition to new wind turbine technologies north of Woodward, OK. The modern turbines have 1.6 MW capacities. 13 THE NO-SLIP CONDITION The development of a velocity profile due to the no-slip condition as a fluid flows over a blunt nose. A fluid flowing over a stationary surface comes to a complete stop at the surface because of the no-slip condition. Flow separation during flow over a curved surface. Boundary layer: The flow region adjacent to the wall in which the viscous effects ( in addition to thus the velocity gradients) are significant. 14 CLASSIFICATION OF FLUID FLOWS Viscous versus Inviscid Regions of Flow Viscous flows: Flows in which the frictional effects are significant. Inviscid flow regions: In many flows of practical interest, there are regions (typically regions not close to solid surfaces) where viscous as long as ces are negligibly small compared to inertial or pressure as long as ces. The flow of an originally uni as long as m fluid stream over a flat plate, in addition to the regions of viscous flow (next to the plate on both sides) in addition to inviscid flow (away from the plate).
Internal versus External Flow External flow over a tennis ball, in addition to the turbulent wake region behind. External flow: The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe. Internal flow: The flow in a pipe or duct if the fluid is completely bounded by solid surfaces. Water flow in a pipe is internal flow, in addition to airflow over a ball is external flow . The flow of liquids in a duct is called open-channel flow if the duct is only partially filled with the liquid in addition to there is a free surface. Compressible versus Incompressible Flow Incompressible flow: If the density of flowing fluid remains nearly constant throughout (e.g., liquid flow). Compressible flow: If the density of fluid changes during flow (e.g., high-speed gas flow) When analyzing rockets, spacecraft, in addition to other systems that involve high-speed gas flows, the flow speed is often expressed by Mach number Schlieren image of the spherical shock wave produced by a bursting ballon at the Penn State Gas Dynamics Lab. Several secondary shocks are seen in the air surrounding the ballon. Ma = 1 Sonic flow Ma < 1 Subsonic flow Ma > 1 Supersonic flow Ma >> 1 Hypersonic flow Laminar versus Turbulent Flow Laminar flow: The highly ordered fluid motion characterized by smooth layers of fluid. The flow of high-viscosity fluids such as oils at low velocities is typically laminar. Turbulent flow: The highly disordered fluid motion that typically occurs at high velocities in addition to is characterized by velocity fluctuations. The flow of low-viscosity fluids such as air at high velocities is typically turbulent. Transitional flow: A flow that alternates between being laminar in addition to turbulent. Laminar, transitional, in addition to turbulent flows over a flat plate.
Natural (or Un as long as ced) versus Forced Flow Forced flow: A fluid is as long as ced to flow over a surface or in a pipe by external means such as a pump or a fan. Natural flow: Fluid motion is due to natural means such as the buoyancy effect, which manifests itself as the rise of warmer ( in addition to thus lighter) fluid in addition to the fall of cooler ( in addition to thus denser) fluid. In this schlieren image of a girl in a swimming suit, the rise of lighter, warmer air adjacent to her body indicates that humans in addition to warm-blooded animals are surrounded by thermal plumes of rising warm air. Steady versus Unsteady Flow The term steady implies no change at a point with time. The opposite of steady is unsteady. The term uni as long as m implies no change with location over a specified region. The term periodic refers to the kind of unsteady flow in which the flow oscillates about a steady mean. Many devices such as turbines, compressors, boilers, condensers, in addition to heat exchangers operate as long as long periods of time under the same conditions, in addition to they are classified as steady-flow devices. Oscillating wake of a blunt-based airfoil at Mach number 0.6. Photo (a) is an instantaneous image, while photo (b) is a long-exposure (time-averaged) image. Comparison of (a) instantaneous snapshot of an unsteady flow, in addition to (b) long exposure picture of the same flow.
One-, Two-, in addition to Three-Dimensional Flows A flow field is best characterized by its velocity distribution. A flow is said to be one-, two-, or three-dimensional if the flow velocity varies in one, two, or three dimensions, respectively. However, the variation of velocity in certain directions can be small relative to the variation in other directions in addition to can be ignored. The development of the velocity profile in a circular pipe. V = V(r, z) in addition to thus the flow is two-dimensional in the entrance region, in addition to becomes one-dimensional downstream when the velocity profile fully develops in addition to remains unchanged in the flow direction, V = V(r). Flow over a car antenna is approximately two-dimensional except near the top in addition to bottom of the antenna. 15 SYSTEM AND CONTROL VOLUME System: A quantity of matter or a region in space chosen as long as study. Surroundings: The mass or region outside the system Boundary: The real or imaginary surface that separates the system from its surroundings. The boundary of a system can be fixed or movable. Systems may be considered to be closed or open. Closed system (Control mass): A fixed amount of mass, in addition to no mass can cross its boundary.
Open system (control volume): A properly selected region in space. It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle. Both mass in addition to energy can cross the boundary of a control volume. Control surface: The boundaries of a control volume. It can be real or imaginary. An open system (a control volume) with one inlet in addition to one exit. 16 IMPORTANCE OF DIMENSIONS AND UNITS Any physical quantity can be characterized by dimensions. The magnitudes assigned to the dimensions are called units. Some basic dimensions such as mass m, length L, time t, in addition to temperature T are selected as primary or fundamental dimensions, while others such as velocity V, energy E, in addition to volume V are expressed in terms of the primary dimensions in addition to are called secondary dimensions, or derived dimensions. Metric SI system: A simple in addition to logical system based on a decimal relationship between the various units. English system: It has no apparent systematic numerical base, in addition to various units in this system are related to each other rather arbitrarily. Some SI in addition to English Units The SI unit prefixes are used in all branches of engineering. The definition of the as long as ce units.
An instrument with many digits of resolution (stopwatch c) may be less accurate than an instrument with few digits of resolution (stopwatch a). What can you say about stopwatches b in addition to d Summary The No-Slip Condition A Brief History of Fluid Mechanics Classification of Fluid Flows Viscous versus Inviscid Regions of Flow Internal versus External Flow Compressible versus Incompressible Flow Laminar versus Turbulent Flow Natural (or Un as long as ced) versus Forced Flow Steady versus Unsteady Flow One-, Two-, in addition to Three-Dimensional Flows System in addition to Control Volume Importance of Dimensions in addition to Units Mathematical Modeling of Engineering Problems Problem Solving Technique Engineering Software Packages Accuracy, Precision in addition to Significant Digits
Pletschet, Cliff Financial Columnist
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