The motion of fluids (gases, liquids and granular material).

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2answers
30 views

Why does the vortex form in the von Karman Vortex Street?

Why does the vortex form in the von Karman Vortex Street? So far I have this for the reasoning: 'It occurs when a fluid flows around a cylindrical object. The pressure on a fluid particle rises to ...
0
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2answers
21 views

Calculating the drag force provided by a laminar flow [duplicate]

If I drop a ball into viscous fluid (e.g. oil), by calculation I know that the fluid flow is laminar. So which equation do I need to calculate the drag force provided by fluid? The drag equation, ...
1
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0answers
24 views

Connection between gas flow rate and diameter of tubing

First time poster, long time troller and curious student. I have a bit of a conundrum that I would love some input on... Here's the problem. I have an air flow system is under constant pressure of ...
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0answers
54 views

Symmetry considerations in Plane Poiseuille Flow

I'm taking a first course on fluid dynamics, and I have this (sort of) conceptual question that's been nagging me for a moment now. I can completely follow the mathematics behind the derivation of the ...
4
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3answers
125 views

Why are vehicles not pitted like golf balls?

I have read that non-laminar flow reduces drag on blunt bodies. Given that, why is pitting not used on motor vehicles?
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0answers
37 views

What am I missing in this reasoning?

In studying the problem of locomotion at low Reynolds number, one possible approach is based on gauge theories. In simple terms, one considers a sequence of shapes of a certain deformable body, say ...
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1answer
46 views

2D aerofoil fluid analysis - find velocity ratio

I just wondered if you could help me out on this fluid mechanics question? I have worked through it myself but am very unsure of my answer (not yet found the pressure difference) the question is ...
2
votes
1answer
73 views

Will changing the pipe diameter reduce the pressure head loss?

I have this system installed in my house (fig 1), and I'm having problems with the shower. I want to know whether, if I change the PEX tubes shown in red from 1/2" to 1" as shown in fig 2, I will have ...
2
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1answer
62 views

Raychauduri equation for Milne universe

I am trying to solve this kind of problem: Consider the Milne model, i.e., the empty $ \kappa = −1 $ Friedmann model. Verify by a direct calculation that the expansion $ \Theta $ of the unit ...
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0answers
25 views

Flow Rate Calculation from a drain tank through a pipe [duplicate]

I want to know how to calculate the flowrate (Q) of a drain tank flowing through a pipe (see the figure below) All I know is that Q=Velocity(V) x Area (A) V= sqrt(2*g*H)=sqrt(2*9.81*10)=14m/s. I ...
0
votes
1answer
34 views

What happens when water added to the ash?

I am pouring some water (using falling by gravity) from my water bottle into the ash. The ash is not in heat conditions. Now the small particles from the ash come out proportional to the water flow. ...
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1answer
26 views

In the non-Newtonian flow, what's the difference between Carreau–Bird model and FENE-P model

Can FENE-P model describe the shear-thinning or shear-thickening flow?
0
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1answer
30 views

Equation of a water pump with a nozzle

If I have a small water pump with a flow f (L/s) and maximal pressure p (bar) and attach its output to a small tube having on the other end a nozzle with an area A (m^2). What is the equation that ...
4
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2answers
120 views

Is Torricelli's law “wrong” for big holes? - Tank draining problem

Consider a tank full of water with a constant cross-sectional area A1 placed vertically on the ground. Now someone drills a hole of an area A2 in the bottom of the tank, and the liquid starts escaping ...
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0answers
55 views

Internal pipe flow - Pressure Drop

Let's say I have internal flow at some flow rate in a pipe that is 10 ft long and there are 2 straight sections and 2 bends. I am trying to determine pressure drop due to friction in the pipe. My ...
0
votes
1answer
23 views

Does the length of a pipe influences the flow?

if I have a closed system of horizontal pipes, filled with water, where I want to create a flow at some rate by using a pump. Does the length of the system influences the flow ? (in real world not in ...
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0answers
42 views

Hamiltonian flow?

I was wondering what the Hamiltonian flow actually is? Here is my idea, I just wanted to know if I am correct about this. So let $(x(t),p(t))' = X_{H}(x(t),p(t))$ are the Hamilton's equations and ...
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0answers
22 views

Hot air particles

I have a question- albeit random one!. I recently visited a friends place who used a standard shovel from the shed as a tool for moving hot charcoals around a pizza oven. Unfortunately the shovel was ...
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0answers
44 views

Expected value, Fluid Mechanics and Momentum balance

I've been doing some problems on Fluid Mechanics involving the balance of Matter and Momentum and I have a question I've been wondering about. Suppose the following: We have a (viscous and ...
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0answers
83 views

Self-made air pump - What does it take to pump up a balloon?

We are building a simple altitude-controlled balloon (idea borrowed from Google Loons). As part of that, we need an air pump to inflate a balloon acting as ballast (which is called a Ballonet in ...
3
votes
1answer
65 views

Air nozzle outlet profile efficiency, concave/convex

I need to design a contracting nozzle for air. The application is quite simple, consider it like an hair dryer but the flow speed is even lower. So the Mach number is very low and the flow laminar. If ...
2
votes
0answers
158 views

Molecular structure correction factor in Mass Flow Controller

This question concerns device called Mass Flow Controller (or Mass Flow Meter). For a video explaining the principle: see https://www.youtube.com/watch?v=G62ma2IFh9o These devices are factory ...
0
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2answers
53 views

Convert cubic feet per sec to feet per sec

Is there a way to convert cubic feet per sec to feet per sec. Or in general volumetric flow to velocity? I want to know the time taken by water to travel from point A to point B. I have the distance ...
0
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1answer
30 views

Influence of a defect on the flow field

I have a long microchannel where flows some water. The reynolds number is much smaller than one. Within the structure of this microchannel there is a big defect. It looks like a bump of size ...
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0answers
33 views

Homogeneous turbulence [closed]

I'm trying to demonstrate the Karman-Howarth expression of isotropic turbulence for the velocity correlation functions: $R_{ij}(r)=A(r)r_ir_j + B(r)\delta_{ij}$ since: \begin{align} A(r) r^2 + ...
0
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1answer
264 views

How to calculate the increased pressure drop due to a restriction?

Assume I have a straight pipe with diameter D1 and a volumetric flow, Q flowing through it. The inlet pressure is P1 and the outlet pressure is P2. Now, assume I've added a restriction in the middle ...
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0answers
77 views

How does a heated constant volume flow behave, for an expanding flow tube leading into the free atmosphere

I have a helium gas flow with a flow rate that has been set to a constant value ($0.3\,m^3/h$). It's streaming upwards in the picture, and beyond the upper big red dot position, it meets the ...
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1answer
148 views

Dependence of streamlined flow on viscosity

My teacher told true class the following statement:- Streamlined flow is more likely for liquid with more viscosity as sturdy flow can only be achieved with slow speed. It's true that viscosity ...
0
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0answers
28 views

Lovely flow rate [duplicate]

How can we calculate the measure of the air flow rate when it is coming out of the balloon? (I mean that which parameter affects that? For example, the measure of balloons neck or the ratios or ...
0
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0answers
18 views

How do I calculate the speed of the air particles flowing out of a balloon? [duplicate]

I am trying to find out what kind of force would a leakage in a balloon cause. What i used is F = (mass flow)speed = (air density)(surface of leakage hole)*speed. I don't know how I could calculate ...
3
votes
1answer
166 views

How does a hollow-point bullet move smoothly through the air, presenting a 'cup-shaped' nose instead of an actual sharp-point to the fluid?

Hollow-point rounds move smoothly through the air when presenting a 'hollow cup-shape' instead of a traditional 'sharp point' to the fluid air. Does this mean the air trapped, and at some assumed ...
1
vote
1answer
184 views

Compute pipe restriction from water flow and static pressure

How can I determine if residential water pipes have a restriction given, for example, flow rate and static pressure? Details: (1) You hook up a static pressure gage to a faucet which is in the ...
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1answer
338 views

What is the differential equation for pressure in a container with an orifice?

I've seen similar problems all over physics.SE and other sites. Most of the time it is about non-compressible fluids, or not about the differential equations. The physical system of interest is ...
2
votes
1answer
415 views

Why are mass flow rates found using Venturi meter and pitot tube different?

Regarding an experiment to find the mass flow rate of a fluid (air) using a venturi meter and a pitot tube: What could be the cause of a variance in results obtained using the 2 instruments mentioned? ...
2
votes
1answer
117 views

Predicting balls's movement in well due to fluid flow

I am a total newbie in fluid dynamics. In one of my experiments/open project, my experiment setup is as below: a small ball sits in a circular well (has mass density a bit heavier than water), with ...
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1answer
247 views

Non-Darcy Flow : Forchheimer plotting method

Recalling Darcy's equation for gas flow, assuming ($z\mu_g$) = Constant $$\tag{1} q_{g,sc}=\frac{kA}{L}\left(\frac{T_{sc}}{Tp_{sc}}\right)\left(\frac{1}{2z\mu_g}\right)(p_1^2-p_2^2)$$ For ...
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0answers
64 views

Books on experimental methods, fluid mechanics related

I need some good books on experimental methods, requirements are: Fluid mechanics related; Thermal, multi-phase etc. topics should be covered; Traditional methods are good, but it would be greater ...
7
votes
1answer
81 views

Do de Laval nozzles have to be asymmetric?

All pictures of de Laval nozzles I've seen have an hourglass shape where the convergent section is shorter than the divergent section. Is this necessary to attain supersonic exhaust velocities, or ...
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1answer
43 views

Sum of velocity fields

In hydrodynamics the for a non-viscous flow the velocity (and density) fields are given by the continuity and Euler equations: $$\rho\frac{\partial \vec{v}}{\partial ...
4
votes
1answer
65 views

Must flow be supersonic for disturbances not to affect upstream?

I'm studying oil production and found a fact that puzzled me. It states that fluid flow downstream of the wellhead must be supercritical in order not to disturb the flow upstream of it. From ...
14
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3answers
407 views

When passed, why does my car 'rock' on the highway when I'm stopped, but not when I'm moving?

I am the blue car in this scenario. If I am stopped on the highway and am passed by a car going fast (about 65 mph), I feel my car rock in the left/right direction. I think I understand why this ...
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0answers
58 views

Home experiment with airfoils and Reynold's number

I want to do an experiment about lowering the Reynolds number of an airfoil moving through air. I want to figure out how to lower the turbulence around an airfoil. So my two hypotheses to lower the ...
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1answer
153 views

How does one figure out how fast water is moving through a water intake on a dam?

Say the dam is Hoover dam for example. The intake is where the water flows in to turn the turbines that generate electricity. I want to know if there is an equation that describes the speed of the ...
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0answers
22 views

Calculate the distance travelled by hot air before it looses its momentum

Hot air is released from a nozzle with certain velocity into the atmosphere. As the stream travels, it looses momentum and after some time mixes with air.How can we calculate the distance the stream ...
0
votes
1answer
47 views

Streamlines for the velocity field $(x, y, 0)$?

Using the equation $$\frac{dx}{x} = \frac{dy}{y}$$ the streamlines for the velocity field $u = (x, y, 0)$ are given by $x = By$ where $B$ is some arbitrary constant. This will give us infinitely ...
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1answer
357 views

Why does the Nusselt Number for a Constant Surface Temperature, Thermally Fully Developed Circular Pipe Converge To a Constant of 3.66?

I have flow in a pipe with a constant surface temperature boundary condition. The velocity profile is fully developed and the temperature profile is also fully developed. In my textbook, it says that ...
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0answers
40 views

hydrodynamic entrance length [developing flow]. Non-native speaker needs some help [closed]

I am currently writing my thesis in English as an non-native speaker. From time to time, I struggle quite a bit with the correct expression of the sentences. Could you have a look on the highlighted ...
0
votes
1answer
130 views

Lubrication Theory

Basically, I'm modelling the flow of a "coating" process -- a fluid flow between a flat moving plane and a stationary cylinder, 2D, cartesian coordinates. Subscript 0 is the at the minimum height b/w ...
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0answers
31 views

Flow in the strip $0 < x < \pi/2$, $y > 0$ [closed]

Could anyone please explain how to show that a complex valued function represents a flow? For example, how does one show that $\Phi(z) = \sec^2 z$, where $z = x + iy$ with $x, y \in \mathbb{R}$, ...
2
votes
1answer
137 views

Fluid flow through an orifice

Forgive me for my ignorance. What would be the method to determine the pressure a non compressible fluid creates when forced though an orifice? Keep in mind this orifice does not have a constant ...