Teorifrågor Flashcards
2022.1
a) In what circumstances (what flow regimes) do you expect to have a hydraulic jump
in a river?
b) What happens to the energy grade line during the hydraulic jump? Explain why.
c) Using the figure below draw the water depths upstream and downstream of a hydraulic jump taking place between section 1 and 2.
d) Sketch on the figure below the energy grade line from section A to section B
a) A hydraulic jump occurs when the flow goes from supercritcal to subcritical.
b) The energy grade line decreases becaus of energy losses due to friction (heat)
The potential energy increases while the kinetic energy decreases.
Difference in kinetic energy is larger than the difference in potential energy which leads to a decrease in total energy.
c) Se anteckningar.
2022.2 A fundamental equation of fluid mechanics has this expression:
𝜌𝑔⃗ = grad P
a) Explain the mathematical and physical meaning of this equation (max 4 points)
b) Make an example of a practical application (2 points)
a) Se bilder
b) This can be used in manometers when the goal is to calculate pressure in a tank. Since 𝜌𝑔⃗ = grad , PA=PB we can calculate PB with pgh=PB and the we also know PA.
Se bilder
III. 3 (max 7 points)
a) Describe the difference between a Newtonian and a non-Newtonian fluid (max 3 points)
b) Describe the difference between Bingham plastic, Pseudosplastic (shear thinning) and Dilatant (shear thickening) fluids.
Show the different behavior of these three fluids on a graph
(Max 4 points)
a)
The rate of Derformation in a newtonian fluid is linear and proportional when shear stress is applied. The rate of deformation for a non Newtonian fluid is not linear, and the deformation curves have varied forms.
b) SE BILD
Binghamn plastic: Acts like a solid until the shear stress becomes large enough to create deformation and then the rate of deformation is linear like a newtonian fluid.
Pseudosplastic: Acts like a “thinner” fluid when the stress increases. A small shear stress creates a small deformation but the deformation increases with an increase in shear stess.
Diliant: Opposite of the pseudosplatic fluids. As the stress increases the rate of deformation decrease. Acts like a thicker fluid with large shear stress.
(max 5 points)
A pipe system brings water from a lower (A) to an upper (B) reservoir, with the help of
a pump (see figures below).
In Scenario 1, both reservoirs are open to atmospheric pressure; in Scenario 2, Reservoir A is open to atmospheric pressure, but Reservoir B is
pressurized.
Draw the hydraulic grade line (HGL) and energy grade line (EGL) for each of the two
scenarios (you can use my sketch below or make your own sketch).
Se bilder
2018.12.1
Explain how you can determine whether the flow in a pipe is laminar or turbulent
To determinant wether a flow is turbulent och laminar you calculate Reynolds number, RE
Laminar: Re ≤ 2000
Turbulent: Re ≥ 4000
Transitional: 2000 ≤ Re ≤ 4000
2018.12.2
Explain what is the critical depth in open-channel flow and how to estimate it. Make an example where you expect to have critical flow.
Critical depth: Occurs when the flow in an open channel has minimum of specific energy. The specific energy refers to sum of depth flow and the velocity head. Froude value = 1
Critical flow: Occurs when the flow velocity in a channel equals the wave velocity generated by disturbance and or obstruction. This occurs for example when a gate is overflowed.
2018.12.3
Explain the difference between Energy Grade Line and Hydraulic Grade Line
The energy grade line, EGL is constant while the hydraulic grade line HGL is constant at constant velocity.
Rita upp
2018.12.4 What is the kinematic viscosity of a fluid?
The kinematic viscosity of a fluid is the ratio between the dynamic viscosity and density.
v = u/p
2016.10.1 What are the major assumptions used in the derivation of the Bernoulli equation?
Provide an example where the application of the Bernoulli equation is not recommended and explain why.
**Assumptions: **
Steady flow
Incompressible flow
Frictionless flow
Flow along streamline
Bernoulli equation states that during steady, incompressible flow with negligible friction,the various forms of mechanical energy are converted to each other BUT their sum remains constant.
Bernoulli equation is not recommended for ex. unsteady flow. Not recommended for gases since they are compressible (density not constant).
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2016.10.2
What is the difference between ideal fluid and real fluid?
**Real fluid: ** Effects due to viscosity that generates shear stress during a fluid motion which tend to resist flow.
Ideal fluid An ideal fluid has no viscosity and is incompressible, density is constant.
2016.10.3 Explain the physical meaning of each term of the momentum equation and provide examples where each term is zero (or could be neglected)
Se bilder
2017.10. 1 Starting from the Bernoulli equation in one point of a river cross section
(see white dot in the figure below), demonstrate that the total energy of water in that cross section can be written as:
2022.12.1 Explain difference between absolute, atmospheric, gage and vaccum pressure.
Se bilder
2022.12.2
What is the difference between uniform and non uniform flow?
At uniform flow, the depth is constant with distance. Uniform flow could only be achived in man made open channels.
At non uniform flow the depth is not constant and varies due to slopes due to ex. topography.
Se bild
2022.12.3
What is viscosity? What is the difference between kinematic and dynamic viscosity? Give an example of when there is viscosity.
Viscosity mesaures the resistance of deformation of at fluid which is the dynamic viscosity. For the newtonian fluids “ekvation”
The kinematic viscosity is the ratio between dynamic viscosity and density.
“thick” liquids have a higher viscosity than “thin” liquids. Ex. honey have higher viscosity than water.
An example of viscosity is when we have a no slip condition. A no slip condition occurs when a fluid in direct contact with a solid sticks to the surface because of viscous effects. Velocity slows down for adjacent layer because of viscous forces between layers. SE BILD
