Questions tagged [fluid-dynamics]
The quantitative study of how fluids (gases and liquids) move.
5,718
questions
0
votes
0answers
36 views
How can I calculate the potential energy between two reservoirs of differentially pressured air held by water?
Ahoy digital heroes!
I'm getting in a right tangle with the below, any help or suggestions would be deeply appreciated.
SCENARIO
Two identical chambers are partially submerged in an infinite volume ...
1
vote
1answer
32 views
How to determine the resultant velocity and height of flow from a vertical stream of water?
For a vertical flow of water that comes into contact with a horizontal surface (eg, water from the tap hitting the base of the sink), given the volume flow rate of the stream, how can I calculate the ...
0
votes
1answer
12 views
Pressure Forces acting on a Hemispherical tank
I am asked to estimate the force due to hydrostatic pressure exerted to a hemispherical container as shown below, due to the fluid which fills the container to $h$.
I first parameterized the surface ...
0
votes
0answers
10 views
Pressure required to clear air bubbles in break lines
It is really tough to manually bleed brake lines for my bike because there are air bubbles where the lines bend. So I was wondering what whether the pressure required to push them out is somehow ...
1
vote
1answer
22 views
Which direction will a truncated cone be pushed by airflow?
Consider the shape below, with the bottom and top faces being holes.
Imagine we hold the shape in place and blow a wind into the big hole.
The air will exit the small end at a higher velocity due to ...
1
vote
1answer
30 views
Radial component of velocity in a Rankine-vortex
A Rankine vortex is a model of a vortex that assumes an inner region ($r<R$) with constant vorticity, $\omega_0$, which rotates as a rigid solid, and an outer region ($r>R$) with zero vorticity, ...
0
votes
0answers
30 views
How can we mathematically express the shape of liquid surface generated by a partly submerged body moving through that liquid? [closed]
Imagine a car moving through a flooded area. As it moves it causes the water in front to rise and level behind it is decreased along with changes in the side. What can be said about the nature of the ...
-1
votes
0answers
52 views
Are complicated equations and mathematical expressions really meaningful and realistic for explaining physical processes? [closed]
To further explain my question:
One of the principles about doing scientific research that I will never forget, is the Occam's razor. Many famous scientists in the history also said something similar ...
0
votes
1answer
43 views
What exactly is $h$ in the bernoulli equation?
I've started with some very basic fluid dynamics, basically what's in Khan academy. The Bernoulli equation, from what I know, relates the pressure to velocity at two different cross-sectional areas of ...
0
votes
1answer
60 views
When you reduce the pressure of a liquid below it's saturation pressure within a container, does it boil or evaporate?
I was playing around with a compressed air can, and it made me think of the greater physics behind what actually happens when I pull the trigger.
I know that compressed "air" cans actually ...
1
vote
0answers
23 views
Conservation of Angular Momentum of an Inviscid Fluid
I was trying to prove that the angular momentum of an ideal MHD plasma, defined by
$\vec{L} = \int \rho \vec{r} \times \vec{u} \ dV$ is conserved when there are no external torques. That is:
$\frac{d\...
0
votes
0answers
30 views
Any lecture notes or easy explanation of Holton's Meteorology?
I am struggling with understanding Holton's Dynamic Meteorology. Any lecture notes based on the book with easy explanations will help.
0
votes
1answer
31 views
Pressure gradient term at low Reynolds number
I was going over the derivation of the dimensionless Navier-Stokes equation, which is explained in this answer. By introducing dimensionless variables in the NS equation, one gets
$$
\frac{D\mathbf u}{...
0
votes
1answer
21 views
Viscous flow over a perfectly smooth surface
Can a viscous liquid flowing over a hypothetical perfectly smooth surface exert viscous stresses on the surface? Can the viscosity of a fluid describe interactions between the fluid and some other ...
0
votes
1answer
29 views
What is the relationship between velocity and time of an object gliding through water?
I took a video of a swimmer pushing off of the wall and gliding through the water until they come to a stop. Using some video analysis software, I was able to plot data points for their velocity over ...
0
votes
1answer
18 views
How can I calculate the pressure at an arbitrary distance from an active spout pumping a compressible fluid?
Say I have a vent pumping a compressible gas into a room.
The newly arrived gas will push the existing gas out of the way to an extent. But also both the new and existing gasses will become compressed....
0
votes
1answer
29 views
Can Brownian motion explain why white smoke moves around in the air?
Can Brownian motion explain why white smoke (fume) generated by chemical reactions moves around in the air?
4
votes
1answer
216 views
What does ultra-rarefied gas mean?
Without using any math, can you explain to me what a rarefied gas is? And then what an ultra-rarefied gas is? I'd like to understand it from a conceptual level if you can make connections to other ...
1
vote
1answer
25 views
Conservation of mass from material derivative
Let the mass be $m=\rho \text{Vol}$, where $\text{Vol}$ is the volume of the domain and the velocity is $u$.
Applying the material derivative, then
$$\frac{Dm}{Dt}=\frac{\partial (\rho \text{Vol})}{\...
2
votes
2answers
56 views
What does $ \mu \nabla^{2} \vec V$ mean in the Navier-Stokes equations?
$$\rho\frac{D \vec V}{Dt}=-\nabla p+ \mu \nabla^{2} \vec V+\rho g$$
In the Navier-Stokes equations there's this term $ \mu \nabla^{2} \vec V $.
I don't really understand what this means. What is the ...
0
votes
0answers
18 views
Euler equation in cylindrical coordinates for axisymmetric fluid flow
The Euler equation in fluid dynamics for spherically symmetric fluid flow reads
$$v_r\frac{dv_r}{dr}+\frac{1}{\rho}\frac{dp}{dr}+\frac{d\Phi}{dr}=0,$$
where, $v_r$ is the radial velocity and $\Phi=-1/...
0
votes
1answer
17 views
Maximum height of the water emerging from a sprinkler
The water in a garden hose is at 140 kPA gauge pressure and is moving at negligible speed. The hose terminates in a sprinkler consisting of many small holes. Find the maximum height
reached by the ...
0
votes
2answers
60 views
Why can't water flow fast when the impact speeds up? (the incompressibility)
I'm a high school student studying physics in Korea! Please understand my poor English skills.
In the text below, the liquid is said to be destructive and incompressible. And he says, "I the ...
1
vote
2answers
27 views
Water flowing after turning off pump
I'm pumping water with a mini pump through a plastic hose (1 meter), between two glass containers. My problem is that if I turn off the pump when the water is flowing through the entire hose, water ...
0
votes
1answer
25 views
Newborn suction force on syringe
Just had a newborn. He requires assisted feeding through a syringe connected to a small catheter.
We place the small bendy catheter in his mouth, so he, simulating natural lactation, sucks the milk ...
2
votes
2answers
105 views
What is (local) pressure within a gas on the microscopic level?
Fluid dynamics view
Fluid dynamics describes liquids and gases in terms of local pressure (among other variables), which varies from a point to point. While mathematically the concept is well-defined (...
3
votes
0answers
92 views
What allows this tornado to form in a frying pan?
I have just seen this video here where a mini tornado has formed in a frying pan:
https://www.youtube.com/watch?v=6CJ-8ze2FjE
Does anyone know how this happens or where I can find an explanation?
1
vote
0answers
20 views
How can i predict the amount of time it would take for my heron's fountain to stop? [closed]
I was assigned a project for my physics class and I'm supposed to build a Heron's fountain and to predict the time it would take to stop so I can then check it experimentally. However, I'm unsure of ...
1
vote
0answers
38 views
Sizing pipes for a filter system with two pumps and one inlet and outlet, bernoulli and venturi?
I need help with a concrete problem that needs solving through good application of physics principles. Here's the problem:
I would like to build a filtering system for my bestway pool, the pool has ...
0
votes
1answer
28 views
Steady flow of a fluid observed in different reference frames
My question is that ,is it possible for a fluid to have steady motion in one frame and non steady motion in another?
0
votes
1answer
31 views
Analyzing Magnus effect from ground frame
How can we explain Magnus effect to the path deviation of a spinning ball assuming the air is still (looking from ground frame)?
I understand that we can use bernoulli principle from ball's frame, but ...
0
votes
0answers
13 views
Is there a characteristic time interval where the continuum assumption doesn't hold?
From my understanding the continuum hypothesis for a fluid doesn't hold in two cases: if the particle body / control medium that is being examined approaches the size of the molecules in the system or ...
0
votes
1answer
37 views
Could you siphon water from a column of water that is supported by buoyancy?
A cylinder with a radius of $10 \;\mathrm{m}$ and a height of $10 \;\mathrm{m}$ is resting on top of a body of water. The cylinder is less dense than water. At the center of the base (equal to water ...
1
vote
1answer
40 views
Normal Shockwaves and its Thermodynamics
Please read this page before going to my question.
When we derive the relation between Mach no. to the left side of the shock wave (M1) and that to the right side of the shock wave (M2),we do that ...
2
votes
2answers
44 views
Since the pressure in smaller bubble decreases why does its radius decreases and not increase, as it should, in the "communicating bubble" experiment?
If we blow two soap bubbles from two communicating pipes with funnels at the ends (see the fig) and close the tube to which they are connected, air will flow from the smaller bubble to the larger ...
0
votes
0answers
22 views
Leaking water from leaky pots
I have two absolutely identical pots with round bottoms. Each bottom has the same number of absolutely identical holes drilled in it. In the first pot, all the holes are quite far apart, while in the ...
0
votes
0answers
29 views
Relativistic hydrodynamics in cylindrical coordinates
I am interested in the study of 'axisymmetric' fluid flows around a compact object in general relativity. I am using the polytropic equation of state, $p=k(s)\rho^\gamma$, and the matter is assumed to ...
0
votes
1answer
49 views
Why doesn't Hydraulic pressure pull two cylinders apart?
Assume as simple hydraulic fixture as shown below.
Where the pipe or hose connects the two, there is a missing area on each cylinder. Wouldn't the hydraulic pressure then create an unbalanced force on ...
1
vote
0answers
12 views
How to calculate the Euler equation for fluids in the newtonian limit from the stress-energy tensor?
I have been working through the exercises of Schutz's a first course in general relativity. In chapter 7 of the book there is a question about the conservation of the spatial components of stress-...
0
votes
0answers
19 views
Doubt related to venturimeter
We connect one limb of manometer at inlet of converging section and other at throat but why we don't connect one limb at throat and other at end of diverging section, is there any problem if we ...
0
votes
0answers
27 views
Why laminar flow does not produce pouring sound while turbulent flow does
I observed in a newly installed tap that it doesn't produce the pouring sound of water (due to a fine mesh on its mouth as I guess) which made me think that it is related to the type of flow (laminar ...
0
votes
1answer
55 views
Floating of steel plate in water
Consider a steel plate, in which orientation will it float in water 'horizontal or vertical' ?
According to me in horizontal orientation plate will float but in vertical orientation it will not float ...
0
votes
0answers
64 views
What was the need for defining kinematic viscosity?
How is kinematic viscosity physically different than dynamic viscosity? What was the need for defining a new quantity ie kinematic viscosity though one can get one from the other? Do try to give a ...
26
votes
3answers
5k views
What is cold wind?
As per my understanding, temperature is the movement of particles in an environment. A highly energetic environment where particles possess high energy has a high temperature,
and low energy means low ...
0
votes
1answer
35 views
Why don't the molecules on the surface of a water drop get pulled down to the bottom of the drop?
When discussing about surface tension, it is said that the surface water molecules experience a net downward cohesive force. If they experience such a force, then why don't the surface water molecules ...
0
votes
0answers
28 views
Why does a garden hose keep its shape when pressurized?
According to the linear momentum equation (time-independent),
$$\Sigma F = \int_{\partial V}dA\bf{V}\rho\textbf{V}\cdot\textbf n$$a u-bend in a garden hose will cause a net force acting on the bend. ...
0
votes
0answers
7 views
Blade angle/design for the high lift to drag ratio
For my high school science fair project I'm trying to build an underwater turbine that would generate the most power. I decided that I would want to find the blade design with the highest lift to drag ...
0
votes
1answer
27 views
Stoke law determend the viscosity of liquid
In an experiment to determine the viscosity by the Stoke method. When we throw the ball into the liquid it will reach a certain mark and start recording the time. This mark what determines its ...
0
votes
0answers
18 views
How can the conservation/Navier Stokes equations (mass, momentum,energy) be modified to model two phase flow in a porous media?
Previously I have seen the derivation of the energy conservation equations for simulation of single phase flow in a porous media (a packed bed). These are the energy equations for the solid and fluid ...
0
votes
2answers
25 views
Can ionized air be used to create airflow without fans or other moving parts?
If I understand it correctly, ionized air should produce an electromagnetic field, which should mean that it can be attracted/reppeled by another field of the oposite/same charge respectively.
If so, ...
