Fließgleichungen

Fließgleichungen, also known as flow equations or constitutive equations for fluids, describe the relationship between stress and strain rate in a flowing material. These equations are fundamental in fluid mechanics and rheology, allowing for the prediction of fluid behavior under various conditions.

The simplest and most common type of flow equation is the Newtonian fluid model. In this model, the shear stress is directly proportional to the shear rate, with the constant of proportionality being the dynamic viscosity. Water, air, and many simple liquids at moderate temperatures and pressures approximate Newtonian behavior.

For non-Newtonian fluids, the relationship between stress and strain rate is more complex and cannot be described by a single viscosity value. These fluids exhibit time-dependent or shear-rate-dependent viscosity. Examples of non-Newtonian fluids include ketchup, paint, blood, and polymer melts. Different models exist to describe their behavior, such as the power-law model, the Bingham plastic model, and the Herschel-Bulkley model, each capturing specific aspects of their flow characteristics.

The development and application of Fließgleichungen are crucial for understanding and engineering processes involving fluid transport, mixing, and deformation. They are essential in fields like chemical engineering, mechanical engineering, materials science, and geophysics. The choice of the appropriate Fließgleichung depends on the specific fluid and the flow regime being considered.