Download PDF by Javier Jiménez: An introduction to turbulence

By Javier Jiménez

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This e-book is meant as a textbook for the senior-level introductory path in hydraulic engineering required in such a lot civil engineering curricula, yet is acceptable for agricultural engineering scholars and others attracted to the topic of hydraulics. this article offers entire remedy of hydraulic engineering in either closed conduit and open channel stream, with examples and difficulties.

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The flow is driven by the motion of the plate, by a pressure gradient in the x À direction, and by the gravitational force g. The constitutive equations of the fluid will be specified below. A steady laminar flow is assumed with the velocity field: vx ¼ vðyÞ; vy ¼ vz ¼ 0 ð3:7:1Þ This is a special case of the flow presented in the previous section. It is further assumed that the fluid sticks to both plates, which provides the boundary conditions: vð0Þ ¼ 0; vðhÞ ¼ v1 ð3:7:2Þ The acceleration is zero and it follows from Eq.

1) are given by the Eq. 25). 25) imply that a top layer of the fluid film flows as a solid plug. The thickness hp of the plug is determined from Eq. 25) are now combined. Because dv=dy is negative, we write the result of the combination as: dv qg sin a sy ¼À ðh À yÞ þ ; dy l l y h À hp ð3:9:18Þ Integration, followed by application of the boundary condition vð0Þ ¼ v0 , gives: ! sy qg sin a h2 2y y 2 À vðyÞ ¼v0 þ y À ; y h À hp h h l 2l ð3:9:19Þ À Á s2y sy h qg sin a h2 À À v1 ¼vp ¼ v hp ¼ v0 þ l 2lqg sin a 2l vp is the plug velocity.

For fluids it is convenient to express the coordinate stresses as a sum of an isotropic pressure p and extra stresses sik : rik ¼ Àpdik þ sik The symbol dik is called a Kronecker delta, named [1823–1891], and is defined by: 0 & 1 0 1 for i ¼ k dik ¼ , ðdik Þ ¼ @ 0 1 0 for i 6¼ k 0 0 ð3:3:18Þ after Leopold Kronecker 1 0 0A  1 1 ð3:3:19Þ Thus dik represent the elements of a 3 9 3 unit matrix 1, which in the coordinate system Ox represents the unit tensor 1. The extra stresses sik are elements in the extra stress matrix T 0 : 0 1 0 1 sxx sxy sxz s11 s12 s13 T 0 ¼ ðsik Þ ¼ @ s21 s22 s23 A ¼ @ syx syy syz A ð3:3:20Þ szx szy szz s31 s32 s33 The extra stress matrix T 0 and the extra stresses sik represent in the coordinate system Ox a coordinate invariant quantity called the extra stress tensor T0 .

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An introduction to turbulence by Javier Jiménez

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