1 Introduction EAS 4101 S11

1 Introduction EAS 4101 S11 - EAS 4101, S10 University of...

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EAS 4101, S10 University of Florida Use Only 1/11/10 1/7 Section 1, Introduction 1 Introduction Aerodynamic forces on a vehicle are due to the surrounding fluid, in this case air, interacting with the vehicle body. Therefore, the study of aerodynamics requires a detailed working knowledge of the basics of fluid mechanics. We will now briefly review a few basic concepts. 1.1 Solids and Fluids The fundamental difference between a fluid and a solid is deformation under shear stress. 1.1.1 Definition of a Solid Substance in which the molecules tend to retain a fixed position . If a shear force is applied, the substance will deform 1 1 2 2 Shear stress produces a shear strain. o For a linearly elastic material, G , where G is the shear modulus o When the force is released the material is returned to essentially its original state (Note: subject to constituent relationships) 1.1.2 Definition of a Fluid Substance in which the molecules are free to move with respect to one another If a shear force is applied it generates a deformation rate (a.k.a. “velocity”) o This isn’t really a black & white issue: e.g. glass, play-dough Could flow or fracture (depend on rate of force application)
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EAS 4101, S10 University of Florida Use Only 1/11/10 2/7 Section 1, Introduction A given shear stress on a fluid will create not a strain, but a strain rate, that is, a deformation rate, in units of length per time (denoted L/t) A given point in the fluid (say on the top surface) will travel a distance L along the shear stress direction for every unit of time t that the force remains applied o When the force is removed, the fluid will not “snap back” like the solid, but rather will retain its new position. What is a Newtonian Fluid? In some fluids, this relationship is governed by a linear viscosity law. We call these Newtonian fluids. o dy du , where is shear stress, is the viscosity (a constant for Newtonian fluids), and du dy is the strain rate.
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This note was uploaded on 09/05/2011 for the course EAS 4101 taught by Professor Sheplak during the Spring '08 term at University of Florida.

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1 Introduction EAS 4101 S11 - EAS 4101, S10 University of...

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