|
The Herschel–Bulkley fluid is a generalized model of a non-Newtonian fluid, in which the strain experienced by the fluid is related to the stress in a complicated, non-linear way. Three parameters characterize this relationship: the consistency ''k'', the flow index ''n'', and the yield shear stress . The consistency is a simple constant of proportionality, while the flow index measures the degree to which the fluid is shear-thinning or shear-thickening. Ordinary paint is one example of a shear-thinning fluid, while oobleck provides one realization of a shear-thickening fluid. Finally, the yield stress quantifies the amount of stress that the fluid may experience before it yields and begins to flow. This non-Newtonian fluid model was introduced by Winslow Herschel and Ronald Bulkley in 1926. ==Definition== The constitutive equation of the Herschel-Bulkley model is commonly written as : where is the shear stress, the shear rate, the yield stress, the consistency index, and the flow index. If the Herschel-Bulkley fluid behaves as a solid, otherwise it behaves as a fluid. For the fluid is shear-thinning, whereas for the fluid is shear-thickening. If and , this model reduces to the Newtonian fluid. As a generalized Newtonian fluid model, the effective viscosity is given as 〔K. C. Sahu, P. Valluri, P. D. M. Spelt, and O. K. Matar (2007) 'Linear instability of pressure-driven channel flow of a Newtonian and a Herschel–Bulkley fluid' Phys. Fluids 19, 122101〕 : The limiting viscosity is chosen such that . A large limiting viscosity means that the fluid will only flow in response to a large applied force. This feature captures the Bingham-type behaviour of the fluid. The viscous stress tensor is given, in the usual way, as a viscosity, multiplied by the rate-of-strain tensor : where the magnitude of the shear rate is given by :. The magnitude of the shear rate is an isotropic approximation, and it is coupled with the second invariant of the rate-of-strain tensor :. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Herschel–Bulkley fluid」の詳細全文を読む スポンサード リンク
|