The quantitative study of how fluids (gases and liquids) move.

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50 views

Volume integral of pressure interpretation

If you have a fluid with with pressure field $p$ what is the physical significance of the the volume integral of the pressure $\int_V p dV$?
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1answer
36 views

Kinetic energy of fluid + collision

When a fluid is flowing, it has of course a kinetic energy and thus we can define kinetic power equal to ρAv v is the velocity and A is the surface of a solid for example. I have a question (maybe it ...
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1answer
43 views

Is there a conclusive correlation between viscosity and surface tension?

I'm working on a project and I need to know if the viscosity effects on the surface tension or not?
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1answer
63 views

Can u explain below diagram is possible or not [closed]

If I takes 3 balloons with same size they r connected with same thred frist end have 2 balloons and second end have 1 balloon I put same manner as shown in diagram then frist end is gos up or not or ...
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1answer
2k views

How to reduce surface tension of water?

I'm working on a project and I need to reduce the surface tension of water. I want you to tell me a way in order to reduce surface tension of water except changing the temperature.
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0answers
63 views

Numerical problem on Viscosity [closed]

A horizontal tube of radius $1\ \mathrm{mm}$ and length $40 \ \mathrm{cm}$ is connected to the bottom of a cubical tank of sides $100\ \mathrm{cm}$ containing water of viscosity $0.01 \ ...
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0answers
34 views

How does Bernoulli's principle produce wing lift? [duplicate]

In the Ray Kurzweil's book How to create a mind is said that: The mathematics of how Bernoulli's principle produces wing lift is still not yet fully settled among scientist [...] What does ...
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2answers
244 views

assumptions about sound waves

When deriving the sound wave equation: $${1 \over c^2} {\partial^2 p' \over \partial t^2 }= \Delta^2 p' $$ by linearizing the Euler equation: $$\rho {d v \over dt }= - \nabla p $$ and the continuity ...
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1answer
87 views

Bernoulli Principle and pressure function

I have read in several places now that for compressible flow the Bernoulli equation $$ \frac {v^2}{2}+ P\ + \Psi = \text{constant}$$ requires: $$P=\int {dp\over \rho(p)} $$ But I don't get ...
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32 views

When can we just look at just the partial derivative of energy?

I am reading a text about fluid mechanics and in the chapter about the (zero viscosity) Wuler equation this showed up: We consider now the kinetic energy and the internal energy of the system and ...
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1answer
73 views

flow rate in split bottleneck

water flows from top to bottom. first there are two pipes, one with 10 LPM max flow rate and another with 20 LPM max flow rate. they both go to another pipe, which is 20 LPM max flow rate. the total ...
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3answers
132 views

Why does Torricelli's law seems to fail when water speeds up after I put my finger in a hose?

We are taught that the speed of the fluid through a hole in a water filled tank obeys Torricelli law: $v=\sqrt{2gh}$, thus the speed is independent of the size of the hole. Why is it then that making ...
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1answer
71 views

What causes loud sound when popping a baloon/bubble?

As I chew my gum, I wonder: when I blow and pop bubbles, what creates the snapping sound? Or similarly, what causes the loud POP when one pops a balloon? Is it the rush of air from inside the pocket ...
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1answer
47 views

Single fluid simulation algorithm

Every fluid simulation I've seen implicitly involves a fluid that isn't mentioned, usually air. This is clear because the simulation usually has an ambient temperature, and always an ambient velocity. ...
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0answers
16 views

Directional resistance in water

How do I calculate the change in resistance in a sealed central heating system, in respect of using a T or y section, I.e, when water flows ⬆️ through a T resistance is split equally at the ...
2
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1answer
80 views

How viscosity and velocity relate in a pipe?

Assume we have a pipe that there is a fluid stream in it. By increasing the velocity of the fluid the resistance will increase either (because of the viscosity I think). My question is how are these ...
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0answers
87 views

Air flow through a tube

During a discussion, a friend explained to me that the volume of air flowing through a tube could be increased up to the point where the air reached supersonic velocity. Presumably the pressure ...
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1answer
56 views

How does air travel after leaving air nozzle?

I am working on a project which involves air nozzles. I am interested in estimating the time it takes for air particles after they leave the nozzle to reach a particular distance away. I have the ...
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1answer
63 views

Why does water not fall out of a pressurized tank? [closed]

Would water fall out of a pressurized container or not? I'm guessing it would because the internal pressure would cause the water to rush out of the container. A capped container contains water under ...
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1answer
38 views

Can a compressible fluid flowing , change its speed in the absence of a pressure gradient?

I've heard that in a high velocity nozzle, any random 'fluid particle' experiences an increase in kinetic energy at the cost of internal energy and pressure energy.And I do understand that for any ...
2
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1answer
186 views

How does hydraulic press work at molecular level?

Let's consider the following arrangement: I know that because of conservation of energy the force on the car has to be amplified. The work $W$ done is $$W = \text{Force} \cdot \text{distance} \, ...
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0answers
23 views

Radiative transfer in a two dimensional slab

I am trying to implement some radiative transfer to a hydrodynamics code. However, all texts that deal with multidimensional radiative transfer assume spherical coordinates, however the hydro code is ...
2
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3answers
118 views

Does this dimensioneless quantity have a name?

When studying creeping flows, a common choice for a characteristic pressure scale is $$p_0 = \frac{\mu_0 U_0}{L_0},$$ where $\mu_0$ is a reference dynamic viscosity, $U_0$ is a reference velocity and ...
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1answer
29 views

Relative magnitudes of pressure gradient force and Coriolis force at midlatitudes

In the midlatitudes, both Coriolis and pressure gradient forces are present in the atmosphere. Can a statement be made about which one of the two forces is bigger in this region?
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1answer
92 views

If I was to poke two holes in a water filled balloon would it lose water twice as fast a a balloon with one hole?

if I was to assume that the only force behind water coming out of the holes is the pressure i.e., the height of the water remaining which is constantly changing (declining) as water leaves the ...
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2answers
563 views

Derivation of Viscous Force

For viscous drag, the formula for the force is, $$ \mathbf F=\pm\eta A\nabla\mathbf u $$ where $\eta$ is the viscosity coefficient, $A$ the area and $\nabla\mathbf u$ the velocity gradient. How is ...
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1answer
63 views

Unsteady Rankine-Hugoniot relations. Is it applicable?

For a unsteady normal shock moving in a medium, the Rankine-Hugoniot relations can be derived, by converting the problem into a steady by fixing the frame of reference on the shock. This idea is easy ...
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1answer
208 views

Relation between pressure and velocity of a fluid

What is the relation between pressure and velocity of a fluid in a closed pipe flow? I used the Bernoulli equation in case of a pipe having non viscous fluid. The pipe is say tilted at an angle and ...
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1answer
179 views

How to calculate leakage flow in a horizontal pipe?

Consider the picture below: The microcontroller takes care of maintaining the pressure $P_1$ constant. In addition, the flow $F$, the area of the pipe ($A_p$) and the area of the hole ($A_h$) are ...
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1answer
72 views

Understanding Stagnation point in pitot fluid

What is stagnation point in fluid mechanics. At the open end of the pitot tube the velocity of the fluid becomes zero.But that should result in accumulation of liquid inside the pipe which is not ...
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2answers
269 views

Hydrodynamics, non-equilibrium thermodynamics and equations of states

Why is it that in non-equilibrium hydrodynamic modelling, e.g. when the solution is time dependent, people use equations of state that are derived from equilibrium considerations (i.e. the ideal gas ...
2
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1answer
58 views

Difference between finite volume, characteristic method and plug flow models of a pipe

I have to model pipes (of a district heating network) with ODE's. My background is computer-science, so it is not that easy for me to understand different approaches. Finite volume approach. Method ...
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1answer
28 views

Is it possible to determine the depth according to waves at the surface of a fluid?

Is it possible to determine the depth of a lake (for example) according to the waves of a stone thrown in this lake ?
2
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1answer
109 views

Physical intuition on vortex sound generation

Whenever a fluid has a nonzero vorticity, it looses some of its energy in a form of sound wave. Formally is this mechanism described by Lighthill's equation or some related model (like e.g. Curle's ...
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3answers
87 views

How does inhalation work?

In school, we learn that during inhalation, the diaphragm expands, causing air to get sucked into our lungs. You can feel this suction by putting your hand over your mouth while inhaling. Why is ...
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0answers
61 views

Bernoulli's Equation for Barotropic Flows

I'm trying to understand a derivation of Bernoilli's Equation and I'm having a hard time understanding the math behind this indentity $$ \frac{1}{\rho} \nabla p = \nabla \int ...
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0answers
30 views

What is meant by the Laminar boundary layer equations?

I have a question and it is to briefly explain (do not derive) the laminar boundary layer equations. I need to understand what the underlying ideas and how the equations are employed. Any help would ...
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0answers
13 views

Fluid motion videos [duplicate]

I am looking for references to papers and research problems involving fluid mechanics, and in particular animal/plant/bacteria locomotion, that could be illustrated by showing a video like these. It's ...
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1answer
28 views

The equation of continuity in isothermal system in spherical axis(transport phenomena)

My homework is about finding the equation of continuity in isothermal systems in spherical axis, I can't imagine a workaround for that since its a little complicated for me to understand velocities ...
2
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1answer
33 views

What are the factors on the volume of a drop?

Earlier today I grabbed a flask of sweetener and reading through the nutrition info I found this "Approximately 0.2cal per 0.2mL or drop". So I started thinking, what affects the volume of a drop? Is ...
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1answer
46 views

A leaf floating on the surface of water (in $x$-$y$ plane) curl along positive $z$ axis [closed]

A leaf floating on the surface of water (in x-y plane) show that for a very small circular leaf ($\nabla \times \overrightarrow v $) is equal to twice the angular velocity of rotation of the leaf, ...
5
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6answers
5k views

What is Pressure Energy?

While deriving Bernoulli's Theorem, our teacher said that the sum of KE, PE and Pressure Energy per unit volume remains constant at any two points. $$P + \rho g h + \frac{\rho v^2}{2} = ...
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1answer
53 views

How does a building lose heat through a gap in the external wall?

Consider a building in a cold climate with a temperature difference of 20 degrees C, i.e. external temp. is 0 degrees C and internal temp is 20 degrees C. How does a building lose heat through a gap ...
2
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2answers
288 views

Wind velocity required to get a flag flying/waving - is there a formula to estimate this?

For example, the giant flags here are 300' x 150 ' with 1,100 lb weight. A question was asked about how much wind would be required to "fly" such a flag given a tall enough flag pole. A Google search ...
2
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0answers
67 views

What causes angular deformation in an inviscid free vortex?

We can describe a two-dimensional (i.e. planar), inviscid, irrotational, free line vortex in cylindrical coordinates with the stream function $\psi = -K\ln{r}$, velocity potential $\phi= K\theta$, ...
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1answer
76 views

What is the difference between the Method of Characteristics being formulated in terms of theta & alpha and theta & nu?

So I'm doing an MSc thesis involving the method of characteristics in rocket nozzles. My lecture notes have the MoC formulated such that the positive characteristics are defined as: C+ = Tan ( ...
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1answer
33 views

Reference values for viscosity and density in incompressible NSE

I come from a pure mathematics background, so I have very limited physics knowledge. I'm currently working out the non-dimensional form for the Navier-Stokes equations and have some questions. Where ...
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1answer
70 views

Navier-Stokes: equation or equations [closed]

In textbooks and papers, you see both forms: the Navier-Stokes equation and the Navier-Stokes equations. Which one is correct and why?
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0answers
31 views

Energy-Mass Equivalence applied to governing equations

To start off with this is an extremely general (vague) questions, and as such I expect vague answers. I've recently been studying the Navier-Stokes equations which govern fluid motion. These ...
0
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2answers
246 views

I have problem understanding the direction of the shear stress [duplicate]

Is it in the direction of the velocity ? If it is, can anybody describe it somehow that matches my physical feeling? How the shear stress affects another layer of fluid ? I faced a question ...