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Introduction to Fluid Mechanics
Chapter 2
Fundamental Concepts
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
‫‪Main Topics‬‬
‫‪ ‬پیوستگی سیال‬
‫‪ ‬میدان سرعت‬
‫‪ ‬میدان تنش‬
‫‪ ‬ویسکوزیته‬
‫‪ ‬تنش سطحی‬
‫‪ ‬دسته بندی حرکت سیال‬
‫‪© Fox, Pritchard, & McDonald‬‬
Fluid as a Continuum
© Fox, Pritchard, & McDonald
Velocity Field
‫چگالی نسبی‬
‫وزن مخصوص‬
© Fox, Pritchard, & McDonald
Velocity Field
Consider also
Steady and Unsteady Flows
1D, 2D, and 3D Flows
Timelines, Pathlines, and
Streaklines
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
:‫جریان‬
‫خط‬
© Fox, Pritchard, & McDonald
‫خط مسیر‬
© Fox, Pritchard, & McDonald
‫رگه‬
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
‫خط مسیر را برای میدان سرعت داده شده بیابید‪.‬‬
‫‪© Fox, Pritchard, & McDonald‬‬
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
Stress Field
© Fox, Pritchard, & McDonald
Viscosity
 Newtonian Fluids
• Most of the common fluids (water, air, oil, etc.)
• “Linear” fluids
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
Viscosity
 Non-Newtonian Fluids
• Special fluids (e.g., most biological fluids,
toothpaste, some paints, etc.)
• “Non-linear” fluids
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
Viscosity
Non-Newtonian Fluids
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
Surface Tension
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
Description and Classification
of Fluid Motions
© Fox, Pritchard, & McDonald
Viscous torque is produced by the annular
gap around the inner cylinder. Additional
viscous torque is produced by the flat
bottom of the inner cylinder as it rotates
above the flat bottom of the stationary outer
cylinder. Obtain an algebraic expression for
the viscous torque due to flow in the annular
gap of width a. Obtain an algebraic
expression for the viscous torque due to
flow in the bottom clearance gap of height b.
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
A viscometer is built from a conical pointed shaft that
turns in a conical bearing, as shown. The gap between shaft
and bearing is filled with a sample of the test oil. Obtain an
algebraic expression for the viscosity μ of the oil as a function
of viscometer geometry (H, a, and θ), turning speed ω,
and applied torque T. For the data given, find by referring to
Figure A.2 in Appendix A, the type of oil for which the
applied torque is 0.325 N m. The oil is at 20C. Hint: First
obtain an expression for the shear stress on the surface of the
conical shaft as a function of z.
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald
© Fox, Pritchard, & McDonald