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In the Boussinesq approximation, variations in fluid properties other than density ρ are ignored, and density only appears when it is multiplied by g, the gravitational acceleration. [ 2 ] : 127–128 If u is the local velocity of a parcel of fluid, the continuity equation for conservation of mass is [ 2 ] : 52
Not all mixing is driven by density changes. Other physical forces may also mix stably-stratified layers. Sea spray and whitecaps (foaming whitewater on waves) are examples of water mixed into air, and air into water, respectively. In a fierce storm the air/water boundary may grow indistinct. Some of these wind waves are Kelvin-Helmholtz waves. [1]
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
Density variations in the atmosphere profoundly affect the motion of water and air. Wave phenomena in air flow over the mountains and occurrence of smog are the examples of stratification effect in the atmosphere. When a fluid system having a condition in which fluid density decreases with height, is disturbed, then the gravity and friction ...
The driving force in stratification is gravity, which sorts adjacent arbitrary volumes of water by local density, operating on them by buoyancy and weight.A volume of water of lower density than the surroundings will have a resultant buoyant force lifting it upwards, and a volume with higher density will be pulled down by the weight which will be greater than the resultant buoyant forces ...
The Richards equation represents the movement of water in unsaturated soils, and is attributed to Lorenzo A. Richards who published the equation in 1931. [1] It is a quasilinear partial differential equation; its analytical solution is often limited to specific initial and boundary conditions. [2]
The weight of the object in the fluid is reduced, because of the force acting on it, which is called upthrust. In simple terms, the principle states that the buoyant force (F b) on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume (V) times the gravity (g) [1] [3]
Turbulent diffusion is the transport of mass, heat, or momentum within a system due to random and chaotic time dependent motions. [1] It occurs when turbulent fluid systems reach critical conditions in response to shear flow, which results from a combination of steep concentration gradients, density gradients, and high velocities.