Flow Regimes – The Physics Hypertextbook
The deep flow is also compared with the single-phase turbulent flow past a circular larger Froude numbers up to with a constant Re / Fr ratio of × High resolution direct numerical simulations and analytical scaling arguments are used to understand the dynamics of turbulence strongly affected by stable. on the motion of settling, bidisperse inertial particles in turbulence (DNS), we examine the effects of Taylor Reynolds number,, and Froude.
The Mach number also doubles as a unit. An airplane flying through the air with a speed equal to the speed of sound in air at that location has a Mach number of 1. It could also be described as flying at Mach 1.
The odd reversal of the usual number-unit sequence to unit-number is unique to the Mach number. The Mach number is meaningful because it is a comparison of the inertial resistance to the compressional resistance experienced by an object moving through a fluid.
When a solid object and a fluid are in relative motion — like a bird flying through the air or the wind blowing around a mountain — it is usually the fluid that yields to the solid. Solids are held together by intermolecular forces and atomic bonds. If the cohesive forces between the particles in a solid are considered significant and long lasting, then the cohesive forces in a liquid are weak and short lived.
In a gas they are virtually nonexistent. You might think that fluids are a pushover for a moving solid, but this is not always the case.
The molecules that make up even the most tenuous of gases won't be able to get out of the way of a solid body moving at a considerable speed. Meteors quite commonly break up on entering the Earth's atmosphere from space. They also burn up, but that is as much an result of frictional heating as it is of trying to push the air out of the way.
Aircraft are known to have broken up during flight from the buffeting effects of moving air on a weakened or damaged part. Therefore in Alaska, a large pipe diameter is required, and the oil is heated. Froude number The Froude number Fr is used to describe the flow pattern over an obstacle. In the case of airflow over a mountain ridge or water over a weirthe current may change accelerate and thin, and then suddenly decelerate, thereby producing a hydraulic jump Fig 2.
Physics > Fluid Dynamics
This jump is sometimes visible as a rotor cloud in the atmosphere but always visible in water, as a bore. Fr is the ratio of the flow speed U to the speed of shallow water waves. Waves do not travel upstream and the flow thickens when crossing an obstacle. A hydraulic jump, i. The prime ' refers to a small perturbation. H ], where H is the height of the mountain.
This leads to orographic rainfall or, if the air is drier, sometimes spectacular lenticular clouds. Imagine airflow crossing a long mountain range whose width W base-to-base equals p.
The Reynolds', Richardson's, and Froude numbers
In this case, there is considerable descent of air on the lee side, since the natural wave motion fits the shape of the mountain, and a series of mountain waves may be found downstream of the range 2. The more stable the air, the higher its natural oscillation frequency.The relation between Turbulence, Reynolds, and Wind Tunnel Testing
And the higher the wind speed and the smaller the mountain obstacles, the higher the triggering frequency will be. A harmonic oscillation results if the two frequencies match.
Froude number - Wikipedia
This may further be amplified if a sequence of mountain ranges exists, each spaced one or an integer multiple m of 'natural' wavelengths m. This sometimes happens over the Basin and Range country of Nevada. In this case the air readily flows over even isolated hills.
In such a situation the wind accelerates slightly, to compensate for the thinned flow channel air mass continuity. The maximum velocity was reached at a height of 34 m above the crest 3. In the rare situation of an unstable atmosphere, the air will spontaneously rise over the mountain, possibly leading to thunderstorms.