# Tagged Questions

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

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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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### what are examples of the Couette flow in nature?

what are examples of the Couette flow in nature? All I could find are theoretical discussions https://en.m.wikipedia.org/wiki/Couette_flow If seems to be the flow of viscous fluid between two ...
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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 ...
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### 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 [on hold]

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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### Why decrease in velocity will increase pressure?

According to the Bernoulli's equation, if velocity decreases, then pressure increases. I am trying to understand the Bernoulli's effect based on a situation. Suppose we have a stream of water. Let'...
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### transform of ship hull cross section to a (half) ellips [closed]

I want to transform a cross section of a ship hull below the waterline to the lower half of a ellipse. In fact the problem can be reduced to the transformation of a two dimensional closed figure that ...
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### Why doesn't flow of liquid from a orifice depend on atmospheric pressure?

While calculating the velocity of efflux, i.e., the velocity of a liquid when it flows from a orifice which is made in a beaker filled with liquid. Since at the orifice, atmospheric pressure acts ...
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### Why is oil more slippery than water? [duplicate]

It is very well known that the higher the viscosity the higher the resistance offered. But why do we slip more on oil as compared with water even if oil has higher viscosity than water?
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### How does shape affect fluid flow for a given section area?

I'm a designer and I have no background in physics and have almost no understanding of fluid behavior. I've been asked to change the dimensions of a reflection chamber on a lab spectrometer. A tube ...
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### Heat transfer in solidification of cylindrical billet

I am trying to plot IN MATLAB the temperature profile of solidification of metal in manufacture of cylindrical billets. The metal is solidifying and the billet moves downwards as a constant water ...
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### How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
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### What would be the optimal diameter of gold grains if you want to fill a pool with them and swim in it?

I was wondering, if I were to fill a pool with gold/gold dust, what would be the optimal diameter of the grains to minimalize the friction to a point at which you would be able to swim in it ((and if ...
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### Which came first, the Crest or the Trough?

We were dealing with 'Interference of light' the other day in class, and our teacher mentioned the 'ripples in water' scenario......and well, that [and not interference in particular] became the bone ...
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### Inlet with variable pressure profile

This is the first time for me here. Consider a pipe with inlet and outlet. This outlet is open to atmosphere. In CFD we can set inlet having variable velocity profile (e.x. parabolic profile) and I ...