Sediments and Fluids Flashcards
(41 cards)
What is the relationship between fluid velocity and pressure?
Along any stream line (path of fluid) fluid velocity varies inversely with fluid pressure.
What is Bernoulli’s equation?
What is Newton’s first law of motion?
Unless a force acts on a body, its velocity will not change.
What is Newton’s second law of motion?
The rate of change of momentum of a body is proportional to the force that acts upon it. F=ma.
What is Newtons third law of motion?
For any force exerted, there is an equal and opposite force.
What is viscosity?
A measure of the resistance of a fluid to deformation.
What is shear stress?
Force per unit area.
What is the rate of shear (velocity gradient)?
For a given fluid subject to a given shear force, the rate of shear (i.e. the gradient of the line of flow between the stationary surface and the moving surface) is constant.
How do you calculate shear stress?
t=μ(du/dz), where μ is viscosity and du/dz is the rate of change of local fluid velocity (u) in the direction z normal to the shearing surfaces at any point.
What are low velocity flows called?
Laminar flow, where the fluid particles travel in regular lines along planes parallel to the base or boundary of the flow.
What is high velocity flow called?
Turbulent flow, irregular turbulent flow.
What is the equation for the Reynolds number?
Re=ρud/μ, where u=fluid velocity, ρ=fluid density, μ=fluid viscosity, d=diameter of pipe.
When does flow become turbulent?
When Re > 2000.
How is laminar flow visualised?
- In linear paths generally parallel to the boundary of the flow.
- At constant velocity.
- Fluid motion is predictable.
- May be analysed by mathematical theory.
How is turbulent flow visualised?
- In irregular sinuous paths.
- With velocity changing (subject to accelerations/deceleration).
- Fluid motion is unpredictable.
- Cannot be analysed by mathematical theory.
- Requires empirical/experimental study.
What are streamlines?
A line that is tangiental to the instantaneous velocity direction. Fluid doesn’t cross the line, and streamlines can’t cross.
What is a pathline?
The trajectory or path of a given fluid particle, may be thought of as the record of a path a fluid particle has taken. They can intersect as different particles may follow different paths at different times.
What is a streakline?
The instantaneous locus or trace or all the fluid particles that pass through a given fixed point in space. If we injected dye continuously from a fixed point - the dye would form a streakline as it passed downstream. Streaklines cannot intersect betcause two particles cannot occupy the same space at the same instant.
What is the characteristics of a steady flow?
When velocity does not change with time, streamlines, pathlines and streaklines are identical.
What are time lines?
The instantaneous location of a line of fluid particles in the flow, usually the initial formed line is perpendicular to the flow boundary. Looking at changes in the shape of a line tells us aboutthe relative changes in flow velocity, e.g. away from a boundary.
What is a streamtube?
A streamtube is an imaginary tube whose talls are streamlines, it may be engisaged as a bundle of streamlines. Just as streamlines cannot cross, so the boundary of the streamtube cannot be crossed. Pipes or channels are essentially stream tubes.
What is the dimensionless form of fluid drag?
CD=f(ρud/μ), where f=fluid drag.
Which forces dominate in the high Re number world?
Inertial forces, or, ρud.
Which forces dominate in the low Re number world?
Viscous forces, or μ
