Tagged Questions

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

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Does fluid speed affect liquid cooling?

If you have a liquid-based cooling system, like the loop in the picture below, does the fluid speed actually matter? I can see how cycling the liquid too slowly would be bad, since the fluid would be ...
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Nozzle vs Orifice Water Jug Draining

why is this happening? Water jug draining So why does the water drain faster when you drain a jug through a funnel compared to the hole you make at the bottom of a jug( the hole is the same size as ...
137 views

Pressure loss in an infinite pipe

I feel lost in this problem. I know pressure loss occurs in a pipe flow due to friction. Say given a constant diameter pipe, if we keep lengthening the pipe horizontally, and static pressure will ...
251 views

Viscosity for steam in the Reynolds number

In calculating the Reynolds number for a flow of steam in a pipe, this is the general formula I am trying to use: $$Re=\frac{\rho d v}{\mu}$$ with density $\rho$, pipe diameter $d$, flow steam $v$ ...
287 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
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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 ...
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Kolmogorov/Energy spectrum for turbulent boundary layer

Previously, I have calculated energy spectrum for 3D isotropic turbulent flow data which is equally spaced in all three directions and then to compute the energy spectrum, one performs Fourier ...
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Why does a soda bottle foam or froth when dropped? [duplicate]

Secondly, if I do drop a soda bottle how long do I have to keep it for it to return to its original state or condition, I.e. safe to open without froth spraying everywhere; or is there some rule of ...
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What are examples of Couette flow in nature?

What are examples of Couette flow in nature? All I could find are theoretical discussions. It seems to be the flow of viscous fluid between two moving plates. I am imagining slipping on an oily ...
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Dynamic water pressure from flow and diameter

I have to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but, I don't have one. After Googling a lot, I found two formulas allowing to compute the ...
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Motion of water droplets on airplane window during takeoff

I observed this while on a flight that took of shortly after it had rained, but could not understand why it happened. The windows of the aircraft had drops of water on the outside. As the flight ...
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Head loss and discharge in a pipe system [on hold]

Two reservoirs, whose surface levels differ by 30m, are connected by a pipe O.6m in diam and 3000m long. The pipeline crosses a ridge whose summit is 9m above the level of and 300m distant ...
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How the wing creates lift? Why critical angle of attack is 16.5" for a supersonic jet and a kite?

I have seen many references on how the wings create lift, most of them overplaying effect of Bernoulli's rule. But nowhere has there been any consideration given to this important factor: Let's ...
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Permeability anisotropy of porous media

Imagine if one were to cut a cylindrical plug out of a perfectly homogeneous rock exactly along one of the principal axis of permeability anisotropy, specifically Kmax. Then, imagine inserting only ...
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Strong and weak turbulence

As far as I understand, in general, turbulence describes the process of transfer of energy from a large scale, at which a system is perturbed, to a small scale, where dissipation happens. At ...
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I'm confused in this dilemma about pressure [on hold]

Bernoulli principle ensures that when cross-sectional area is small the velocity will increase and so the pressure decrease. So, in a pump the outlet hose area controls the pressure and velocity of ...
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reference request: 2D turbulence

I'm reading papers regarding the 2D Navier-Stokes equations. But I don't have a physics background. Would anybody come up with some introductory references of 2D turbulence which contain the following ...
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Equilibrium between two water tanks

I've been reading about hydrostatic theory, however I couldn't find a similar case/exercise about my basic problem. I have two water tanks (same size) filled with different water heights, and ...
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How does viscosity cause dissipation? [closed]

I am not a physicist so bear with me. I'm trying to understand the mechanism through which energy is dissipated in a fluid or solid. Often the explanation is that it happens due to viscosity or ...
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velocity of liquid in hydraulic motor

Does the speed of liquid in the hydraulic motor eye affects the revolution Per minute of the motor? So if i changed the diameter of the hose of the motor will this change any thing in the motor?
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Pressure of hydraulic motor

If I regulated the hydraulic pressure of any hydraulic motor (external gear), wouldn't it change according to Bernoulli principle when it enters the cavity of the motor to push its teeth (as the area ...
117 views

How to stop water flow in a siphon?

I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it off....
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Hydraulic fluid velocity [closed]

in a pic like this would the speed of liquid at the inlet change anything ?
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Derivation of the equation for flow of a viscous liquid on a rotating disk

In this paper, Emslie, Alfred G., Francis T. Bonner, and Leslie G. Peck. “Flow of a Viscous Liquid on a Rotating Disk.” Journal of Applied Physics 29, no. 5 (1958): 858. doi:10.1063/1.1723300. ...
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Sum of forces with liquid in rotation

It's not homework (I'm teacher). I would like to compute sum of forces on this study : The shape is symmetrical like that I'm sure the center of gravity is in the center of the shape. I compute ...
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Irreducible liquid saturation preparation

When preparing a porous medium such as a rock to a "residual" or "irreducible" liquid (oil or water/brine) saturation, what is the best practice? The second fluid phase that fills the remainder of the ...
15 views

Vorticity and circulation in potential flow

There is a plenty of situations where the vorticity $\vec{\omega} = \nabla \times \vec{u}$ is zero all over the system (i.e. potential flow) and yet the circulation $\Gamma$ is nonzero (e.g. ...
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Meaning of $\nabla_{\mathbf{p}_k} W(\mathbf p, h)$ in PBF

I'm reading this paper on Position Based Fluids and I couldn't understand the meaning of $\nabla_{\mathbf{p}_k} W(\mathbf{ p_i - p_j}, h)$ in the equation 7 (see below). …the gradient of the ...
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What is atmospheric stratification?

In the context of atmospheric stability, what are the meanings of stable or unstable stratification? What is stratification?
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When is a flow a shear flow?

Let us say I have a velocity profile of a flow: $$\vec u= \begin{pmatrix} v_x \\ v_y \\ v_z \end{pmatrix}$$ Under what circumstances would this be called a shear flow? And can we say anything for an ...
186 views

Flow through a rifled pipe

In turbulent flow the friction is inertial for the most part: the chaotic flow causes the fluid in the faster moving center to interchange randomly with the fluid near the edge. This eventually allows ...
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In scientific literature, we know that the condition for incompressible flow is that the particular derivative of the fluid density $\rho$ is zero: $$\frac{D\rho}{Dt}=0$$ and for steady flows the ...
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How do we calculate the speed of an air bubble rising in water?

We all know that an gas bubble expands as it rises through a liquid due to decreasing pressure.But at what speed does it rise? if we make a bubble of unit volume filled with a gas of given density at ...
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How much approximately the pressure would drop?

A container made from from aluminium ($0.5~\mathrm{mm}$ thickness $10^3~\mathrm{cm^3}$) closed system , it has 50 psi (nitrogen) pressure inside at temperature $80^\circ~\mathrm C.$ Approximately : ...
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What is the name of matter with $w = - \frac{1}{3}$?

What kind of "matter" is described by the following thermodynamic relation ? $$\tag{1} p = -\, \frac{1}{3} \; \rho,$$ Where $p$ and $\rho$ are the pressure and density ...
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how does it come that atmospheric pressure does not cut off blood flow in blood vessels? [duplicate]

We know that atmospheric pressure is 760mmHg, whereas blood pressure in blood vessels is somewhere between 80 to 120 mmHg. As outer pressure is higher than inner so shouldn't it cut off the blood flow?...
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Atmospheric pressure changes on plastic bottle containing a liquid

We have a problem at work and I need some help on a theory. We ship a liquid in plastic bottles using a pump closure. Recently some of the bottles have been arriving to customers having leaked. The ...
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How is the pressure energy term equal to atmospheric pressure here?

I was looking up at the derivation of Torricelli's law in my textbook: $$P_a + \frac{1}{2}{\rho}v_1^2 + \rho gy_1=P + \rho gy_2$$ This is the equation representing one of the steps for its ...
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Is Gas flow rate or Volumertric flow rate right one to use for thick wall?

I will make container from steel or aluminium ( 0.5 mm thickness ) and fill it with air (2 bar) and I want to know how much pressure would the container loose overtime (20 years) ? I have asked this ...
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Bernoulli equations when different fluids and volumetric flow rates are involved

I have doubts on the use of Bernoulli equation when multiple volumetric flow rates are involved. Consider for istance the device in picture. Water flows in the main tube, while in the tank below ...
12k views

Sound - what happens with the particles when a wave passes

I'm having some problems in understanding the principles of sound propagation. The wave propagates though air (for example) exerts compression, which is followed by rarefaction. I think I got than ...
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Calculation of Drag coefficient for infinite cylinder

I would like to calculate the drag coefficient for an infinite cylinder for various Reynolds numbers. I'm using $C_D=\large{\frac F{\frac 12Av^2\rho}}$ My question is how do I calculate force ? ...
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Does a venturi injector contradict the 2nd law of thermodynamics?

The picture below shows a venturi injector. When the water flow enters the narrower cross section its velocity increases and its pressure decreases. Subsequently, fluid is sucked (or injected) into ...
1k views

What can wavy patterned sand tell about the Fluid that formed it?

Sand on the bottom of the ocean as well as sand on the low-tide beach often forms wavy patterns. Do the parameters of these wavy patterns have any relation to the water and waves that formed them? If ...
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Is spectroscopic analysis of flowing air sensitive to the amount of matter or the flux?

I would like to like to go deeper in understanding the analytical and physical behaviour of air quality analysers. AQ analysers are merely based on spectroscopy (absorbance, fluorescence, ...
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Why is momentum conserved in a control volumen?

I know momentum is conserved in an isolated system wherein there in not mass nor energy flow and the net resultant external forces are equaly to zero. My doubt is when I'm studying a (fixed) constrol ...
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Bernoulli equation: energy conservation in moving reference frames

I get a bit confuse with the use of Bernoulli equation in moving (inertial) frames. Consider the following example. The tube in picture is moved with velocity $u$ inside a tube where fluid moves with ...
107 views

Deriving an Euler Equation

In this derivation is it necessary to write the triple integral, as I thought that if we are dealing with one fluid particle it only contains one "point" and hence we do not have to take a sum?