Solutions Manual For Fluid Mechanics: Fundamentals and Applications 3rd Edition By Yunus A. Çengel & John M. Cimbala || All Chapters | Latest & Updated Version 2024
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Solutions Manual for Fluid Mechanics: Fundamentals and
Applications Third Edition Yunus A. Çengel & John M.
Cimbala McGraw-Hill, 2013 A+
Chapter 1: Introduction, Classification, and System
1-1 C
Solution We are to define a fluid and how it differs between a solid and a gas.
Analysis A substance in the liquid or gas phase is referred to as a fluid. A fluid differs from
a solid in that a solid can resist an applied shear stress by deforming, whereas a fluid deforms
continuously under the influence of shear stress, no matter how small. A liquid takes the shape of
the container it is in, and a liquid forms a free surface in a larger container in a gravitational
field. A gas, on the other hand, expands until it encounters the walls of the container and fills the
entire available space.
Discussion The subject of fluid mechanics deals with ball fluids, both gases and liquids.
1-2 C
Solution We are to determine whether the flow of air over the wings of an aircraft and the
flow of gases through a jet engine is internal or external.
Analysis The flow of air over the wings of an aircraft is external since this is an unbounded
fluid flow over a surface. The flow of gases through a jet engine is internal flow since the fluid is
completely bounded by the solid surfaces of the engine.
Discussion If we consider the entire airplane, the flow is both internal (through the jet
engines) and external (over the body and wings).
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1-3 C
Solution We are to define incompressible and compressible flow, and discuss fluid
compressibility.
Analysis A fluid flow during which the density of the fluid remains nearly constant is
called incompressible flow. A flow in which density varies significantly is called compressible
flow. A fluid whose density is practically independent of pressure (such as a liquid) is commonly
referred to as an “incompressible fluid,” although it is more proper to refer to incompressible
flow. The flow of compressible fluid (such as air) does not necessarily need to be treated as
compressible since the density of a compressible fluid may still remain nearly constant during
flow – especially flow at low speeds.
Discussion It turns out that the Mach number is the critical parameter to determine whether the
flow of a gas can be approximated as an incompressible flow. If Ma is less than about 0.3, the
incompressible approximation yields results that are in error by less than a couple percent.
1-4 C
Solution We are to define internal, external, and open-channel flows.
Analysis External flow is the flow of an unbounded fluid over a surface such as a plate, a
wire, or a pipe. The flow in a pipe or duct is internal flow if the fluid is completely bounded by
solid surfaces. The flow of liquids in a pipe is called open-channel flow if the pipe is partially
filled with the liquid and there is a free surface, such as the flow of water in rivers and irrigation
ditches.
Discussion As we shall see in later chapters, different approximations are used in the analysis
of fluid flows based on their classification.
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Solution We are to define the Mach number of a flow and the meaning for a Mach number
of 2.
Analysis The Mach number of a flow is defined as the ratio of the speed of flow to the
speed of sound in the flowing fluid. A Mach number of 2 indicate a flow speed that is twice the
speed of sound in that fluid.
Discussion Mach number is an example of a dimensionless (or nondimensional) parameter.
1-6 C
Solution We are to discuss if the Mach number of a constant-speed airplane is constant.
Analysis No. The speed of sound, and thus the Mach number, changes with temperature
which may change considerably from point to point in the atmosphere.
1-7 C
Solution We are to determine if the flow of air with a Mach number of 0.12 should be
approximated as incompressible.
Analysis Gas flows can often be approximated as incompressible if the density changes are
under about 5 percent, which is usually the case when Ma < 0.3. Therefore, air flow with a Mach
number of 0.12 may be approximated as being incompressible.
Discussion Air is of course a compressible fluid, but at low Mach numbers, compressibility
effects are insignificant.
1-8 C
Solution We are to define the no-slip condition and its cause.
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Analysis A fluid in direct contact with a solid surface sticks to the surface and there is no
slip. This is known as the no-slip condition, and it is due to the viscosity of the fluid.
Discussion There is no such thing as an inviscid fluid, since all fluids have viscosity.
1-9 C
Solution We are to define forced flow and discuss the difference between forced and
natural flow. We are also to discuss whether wind-driven flows are forced or natural.
Analysis In forced flow, the fluid is forced to flow over a surface or in a tube by external
means such as a pump or a fan. In natural flow, any fluid motion is caused by natural means such
as the buoyancy effect that manifests itself as the rise of the warmer fluid and the fall of the
cooler fluid. The flow caused by winds is natural flow for the earth, but it is forced flow for
bodies subjected to the winds since for the body it makes no difference whether the air motion is
caused by a fan or by the winds.
Discussion As seen here, the classification of forced vs. natural flow may depend on your
frame of reference.
Solution We are to define a boundary layer, and discuss its cause.
Analysis The region of flow (usually near a wall) in which the velocity gradients are
significant and frictional effects are important is called the boundary layer. When a fluid stream
encounters a solid surface that is at rest, the fluid velocity assumes a value of zero at that surface.
The velocity then varies from zero at the surface to some larger value sufficiently far from the
surface. The development of a boundary layer is caused by the no-slip condition.
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