11. Bernoulli's Equation ignores compressibility of the fluid, as well as the effects of gravity and viscous forces on the flow. 12. Turbulence kinetic energy is then transferred down the turbulence energy cascade, and is dissipated by viscous forces at the Kolmogorov scale. 13. :I think the term passive force refers to something like friction or viscous force , which only exist as resistance to motion. 14. The obvious problem in the above method is the neglection of viscous forces which contribute heavily in modes of motion like roll. 15. In observations of vortices in real fluids the strength of the vortices always decays gradually due to the dissipative effect of viscous forces . 16. A low Reynolds number ( " Re " < < 1 ) indicates that viscous forces are very strong compared to inertial forces. 17. Integration of the viscous force per unit area "'? "'over the sphere surface gives the frictional force " F d " according to Stokes'law. 18. Assuming also that the wave height is very small compared to the mean height ( ), we have ( without lateral viscous forces ): 19. On an aircraft wing the boundary layer is the part of the flow close to the wing, where viscous forces distort the surrounding non-viscous flow. 20. Instabilities in the flow are not present, i . e . perturbations to the flow are damped out by viscous forces , and the flow is steady.
