Stokes flow refers to the flow of an incompressible viscous fluid at low Reynolds numbers, where inertial forces can be neglected in comparison to viscous forces. This type of flow is governed by the Stokes equations, which are simplified forms of the Navier-Stokes equations. These equations assume that the fluid is Newtonian, meaning its viscosity is constant and the stress is linearly proportional to the rate of strain.
Stokes' paradox refers to a phenomenon in fluid dynamics that highlights an apparent inconsistency in the flow of a viscous fluid around an object. The paradox is named after the British mathematician and physicist George Gabriel Stokes who analyzed the flow of a viscous (incompressible) fluid around a cylinder. The paradox arises when considering a two-dimensional flow of a viscous fluid past an infinitely long, solid cylinder.
The Shallow Water Equations (SWE) are a set of hyperbolic partial differential equations that describe the flow of a thin layer of fluid, such as water in rivers, lakes, and coastal areas. These equations are particularly useful in hydraulic and environmental engineering for modeling phenomena like flooding, tsunami propagation, and sediment transport. The SWE are derived under the assumption that the horizontal length scale of the fluid flow is much larger than the vertical scale of the fluid depth.
The relativistic Euler equations are a set of equations that describe the dynamics of perfect fluids in the context of relativistic physics. They extend the classical Euler equations, which govern the flow of inviscid (non-viscous), incompressible fluids, to situations where the speeds involved approach the speed of light, or in contexts where relativistic effects are significant, such as in astrophysics or cosmology.
The Rayleigh–Plesset equation is a fundamental equation in the field of fluid dynamics, particularly in the study of cavitation—a phenomenon where vapor bubbles form and collapse in a liquid. The equation describes the dynamics of a spherical gas bubble in an incompressible liquid, accounting for the effects of pressure, surface tension, and viscous forces.
Rayleigh's equation in fluid dynamics refers to a fundamental principle that describes the stability of a fluid flow. It is often associated with the stability analysis of boundary layers and the onset of turbulence and instabilities in various fluid flow situations. One common context in which Rayleigh's equation is discussed is in the study of stability of various flow regimes, particularly in relation to the growth of instabilities in a shear flow. The equation is typically derived from the Navier-Stokes equations under specific assumptions and conditions.
The Rankine–Hugoniot conditions are a set of mathematical conditions used in fluid dynamics and gas dynamics to describe the behavior of shock waves and discontinuities in a medium. These conditions relate the values of physical quantities (such as pressure, density, and velocity) on either side of a discontinuity, which can be a shock wave or a contact discontinuity.
The Oseen equations are a set of equations that describe the steady-state flow of a viscous fluid. They can be seen as a linearization of the Navier-Stokes equations, which govern the motion of fluid substances. The Oseen equations are particularly useful in the study of low Reynolds number flows, where inertial forces are negligible compared to viscous forces.
The Orr–Sommerfeld equation is a fundamental equation in fluid dynamics that describes the stability of an incompressible flow, particularly in the context of boundary layer theory. It is named after William Richard Orr and Arnold Sommerfeld, who contributed to its development. The equation arises when analyzing small disturbances or perturbations in a basic flow profile. It is particularly important in studying the stability of laminar flows and understanding transition to turbulence.
The Morison equation is a mathematical model used in engineering, particularly in the fields of civil and ocean engineering, to estimate the wave forces on structures such as offshore oil platforms, wind turbines, and coastal structures. It accounts for both the inertia and drag forces acting on a structure submerged in a fluid, such as water.
The mild-slope equation is a mathematical representation used in coastal engineering and fluid dynamics to describe the propagation of surface water waves over varying bathymetry (the underwater equivalent of topography). It is especially useful for analyzing wave behavior in coastal areas, where the depth of the water changes gradually.
The Kármán–Howarth equation is a fundamental relation in fluid dynamics, particularly in the study of turbulence. It describes the evolution of the second-order velocity correlation function in an incompressible flow. The equation provides insight into the relationships between different scales of motion in turbulent flows. In turbulent fluid mechanics, the velocity field can be characterized using correlation functions, which measure the statistical relationships between the velocities at different points in space.
The Kozeny-Carman equation is a mathematical model that describes the flow of fluids through porous media. It relates the permeability of a porous material to its porosity and specific surface area. It is widely used in fields such as hydrogeology, petroleum engineering, and soil science to analyze how fluids move through soils and rocks.
The Korteweg–de Vries (KdV) equation is a third-order nonlinear partial differential equation that describes the evolution of waves in shallow water. It is significant in various fields, including fluid dynamics, nonlinear wave theory, and mathematical physics.
Kelvin's circulation theorem is a fundamental principle in fluid dynamics, particularly in the study of inviscid (non-viscous) and irrotational flows. It states that the circulation around a closed contour moving with the fluid is constant in time, provided the flow is conservative and the fluid is incompressible and inviscid.
The Kadomtsev–Petviashvili (KP) equation is a fundamental nonlinear partial differential equation (PDE) that describes the propagation of waves in a quasi-one-dimensional medium. It arises in various fields such as fluid dynamics, plasma physics, and nonlinear optics. The equation serves as a higher-dimensional generalization of the Korteweg–de Vries (KdV) equation, which describes solitons in one dimension.
A Herschel–Bulkley fluid is a type of non-Newtonian fluid that exhibits both yield stress and shear-thinning (or shear-thickening) behavior. The defining characteristic of such fluids is that they do not begin to flow until a certain threshold stress, known as the yield stress, is exceeded. Once this yield stress is surpassed, the fluid flows according to a power-law relationship that describes its viscosity.
The Hazen–Williams equation is an empirical formula used to calculate the flow of water through pipes, specifically in civil engineering and hydraulics. It estimates the head loss (pressure loss due to friction) in a pipe based on the flow rate, pipe diameter, and the roughness of the pipe's interior surface. The equation is particularly applicable for water flow in pipes where the flow is turbulent. The general form of the Hazen–Williams equation is: \[ h_f = 0.