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

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Helmholtz decomposition allows incompressible flow with an irrotational component?

A vector field can be written in terms of irrotational and a divergence-free components. Using a 2D velocity field as an example, $ \vec v = -\nabla \phi + \nabla \times \vec \Psi$ Where $\vec \Psi$ ...
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1answer
43 views

Simulating supersonic flight in game

So this question about how to implement a good looking simulation of super-hypersonic flight of a rocket from launch point to orbit. I have an idea how to implement a good looking aerodynamic on ...
3
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3answers
322 views

Effect of initial suction power on siphon performance

Background I have a flooded crawl space and I'm using a long hose to siphon the water out. I do this as follows: One side of the hose is in the crawl space, and the other side down a hill in the ...
3
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1answer
71 views

A model for constant temperature of water in a container

I put some water in a container with initial temperature $T_0$ in a room, and the room's initial temperature is $T_a$. Now the container is filled to the maximum, so any more water coming in will ...
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1answer
54 views

How does water at different temperatures behave when they are mixed? [closed]

If I were to inject a constant flow of water at T1 into a reservoir of water at T2, how does that effect the temperature of the mixture at different points in the reservoir? In other words, what ...
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2answers
43 views

How do the Americas Cup Yachts sails work?

With the vast majority of sailing boats its pretty evident how the sails work to harness the energy of the wind to propel themselves forward. However on the modern Americas cup foiling yachts i can't ...
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2answers
68 views

Misunderstanding about Reynolds number

I am confused about Reynolds number. I am trying to use the formula to see if NASCAR cars have laminar or turbulent flow. But I am not sure how exactly to use the equation in order to do such ...
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1answer
164 views

Application of Stoke's Law

I was looking at Stoke's law and it says that you use it to calculate the drag force on a sphere passing through a fluid. Can i also use this equation to calculate the drag force on a car going ...
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1answer
37 views

Power vs. Speed - Indoor rowing

In the sport of indoor rowing (and probably others) I know that to double your speed you must increase your power output by a factor of eight. I am wondering why this is the case. The indoor rower ...
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1answer
74 views

Determining intake pressure of a cannula returning blood to an ECMO circuit

What are we trying to figure out: We want to know if it is possible to determine the pressure of the inlet for the catheter that returns deoxygenated blood to the ECMO system to help prevent ...
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0answers
27 views

Could a hydrophobic surface increase a liquid's resistance to compression/displacement?

Imagine a quantity of an aqueous (yet slightly viscous) solution is resting on a hydrophobic surface with a contact angle around 100°. A downward force is then applied as a (repellant) surface is ...
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2answers
78 views

Viscous forces with asymmetric gradient velocity in fluid mechanics

In fluid mechanics, the stress tensor writes $\sigma = -p 1 + \tau$ where the deviatoric part $\tau$ corresponds to shear. The viscous (volumic) forces are $\operatorname{div}\tau$. For a Newtonian ...
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11 views

Hydraulics: Booster bore variance - pedal travel (car)

I want to install an inline (remote) VH44 booster (vacuum assist "brake booster"), which has a 5/8" bore. My master cylinder (in this case, I'm installing it on the clutch line) has a 3/4" bore. ...
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3answers
115 views

How does the cross section of a stream of falling water decrease

Consider a continuous stream of water flowing down from a tap. Since the water flow is continuous, by equation of continuity, the cross sectional area of the stream decreases. But what makes the water ...
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1answer
45 views

What fluid dynamics equations are like in zero gravity?

I don't know if this is a proper question. I am not so familiar with fluids. I am just curious about what Navier-Stokes equations for fluids will look like in zero gravity. Are they stay the same? If ...
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1answer
63 views

What is actually the characteristic length in fluid dynamics description?

In many fluid-dynamics models and quantities (Reynolds number, Strouhal number... generally various turbulent flow descriptions) there is a parameter (usually $L$ or $\ell$) descripted as ...
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0answers
27 views

Extension of the advection diffusion equation with diffusion perpendicular to the flow

Assume you model particle flow in fluid in a cylinder by an advection-diffusion equation, thus taking into account both diffusion and bulk flow. What would happen to the model if you would, at some ...
3
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1answer
52 views

Does a trumpet play at a tritone lower without lip vibration?

My trumpet teacher noticed that if you blow into a trumpet for warm-up, without any lip vibration, there is still a slightly audible pitch which is a tritone lower than "expected" in the following ...
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0answers
18 views

What result would I get from series-mounted vacuum assist? (hydraulic vacuum assist)

If I install two inline vacuum assist devices (such as VH44) on my clutch line, what will change in comparison to having a single boost? Will it decrease pedal travel? Tension? Both? Neither? Lest ...
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1answer
51 views

Derive drag coefficient of plate

There is any analytical way to derive drag coefficient of flat plate aligned perpendicular to the flow? Wikipedia says it's between 1.98~2.05 but I want to get this value in calculation, not ...
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1answer
49 views

A thermometer in the wind

Consider two cases, Situation 1: a thermometer is stationary and air is blowing past it. Situation 2: the thermometer is moving with the wind, say on a car or something. Assuming now friction ...
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0answers
21 views

Expansion of Lighthill source term problem

Studying M. S. Howe's Theory of Vortex Sound I need to compare following two approximations of Lighthill's source term $L$: $$ L_1 = \mathrm{div} \hspace{2pt} (\omega \times v) $$ $$ L_2 = ...
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1answer
36 views

Ratio of force of resistance due to liquid to that due to gravity

What is ratio of force of resistance due to liquid to that due to gravity? For any object for example a ball falling in a liquid with constant velocity, what will be the ratio?
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1answer
51 views

Fluid dynamics question [closed]

Consider 2 cubes one resting horizontally with a hole at the bottom corner , we can say that the speed of water coming out of there is sqrt(2gh) if the hole is considerably small , what about the rate ...
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1answer
75 views

dynamics&forces of hydrofoil wave surfing

I'm puzzled by apparent ability of hydrofoil to surf [ocean's] wave, as evidenced by this footage. Let's compare it to ordinary surfboard. Let's focus on "static" condition when the board is position ...
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1answer
38 views

A cylindrical vessel open at the top

A cylindrical vessel open at the top is 20cm high and 10cm in diameter. Circular hole whose cross-sectional area 1 cm² is cut at the centre of the bottom of the vessel water flows from a tube above ...
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0answers
28 views

Why do very small balls attached to a tiny spring propel themselves in hardly moving fluids? [duplicate]

I recall watching a youtube video about a ball with a spring on the idea propelling themselves through stable fluids without any assistance, even if we make sure the spring isn't moving in the ...
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1answer
29 views

Does groundwater flow depend on the geometry of the aquifer?

I consider two cases of a confined aquifer and want to calculate the pressure / hydraulic head in a quasi 1d case. These two cases are shown in my drawing. I assume homogenious, isotropic darcy ...
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4answers
234 views

What is the real cause of the boiling (forming of bubbles) of water?

I've got a question about the boiling of water. I'm a first year physics student and from the Netherlands. I've searched alot about the boiling of water and this confused me. Everyone said something ...
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1answer
48 views

Pressure gradients at two different sized holes separating 2 chambers at different pressures [closed]

Why is the pressure gradient by the simplified Bernoulli equation higher at the smaller hole?
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2answers
63 views

How to estimate wind speed from a pressure difference?

Does a formula (or a rule of thumb) exist to estimate the wind speed between a high pressure area and a low pressure area given the pressure difference between the two areas? Only the wind resulting ...
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1answer
25 views

Coherence of pressure and mass flow in a pipe [closed]

What is the coherence of pressure and mass-flow in a horizontal pipe? Let's assume I have just one pipe with pressure = 1.5 bar at the input and through pressure-losses 1.2bar at the output. Is there ...
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2answers
82 views

Is the force exerted by the container on the fluid and the force exerted by the liquid on the container equal?

I came across a question where i was asked to find the force exerted by the walls of a frustum shaped bucket on a liquid inside it . I found the force exerted by the liquid on the walls of the bucket ...
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1answer
37 views

How to model terminal velocity as a function of gravitational acceleration?

Taking the most simplistic form of terminal velocity, $v=\sqrt{\frac{mg}{c}}$ I want to try and derive an equation that models the velocity as g changes in height.. Because obviously the terminal ...
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1answer
44 views

How do you calculate force in a cone full of fluid? [closed]

I have no idea how to calculate the force the sides of the cone exert to the fluid (when the cone is at least partly filled with fluid) Can someone help me? A link or a short explanation will do
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5answers
273 views

Momentum of slowly spinning (viscous) fluid

If we have a massless cylindrical container (or radius $R$) with a liquid of certain density $\rho$ and viscosity $\mu$ at rest. Then at time zero we impart a constant rotational velocity $\Omega$ on ...
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0answers
81 views

Why Velocity is referred as momentum? [closed]

In many text books the velocity is referred to as a linear momentum which is being convected. For example the table in the following page My old conception is that the momentum or more precisely ...
3
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1answer
197 views

Ideal shape of a water clock

The ancients undoubtedly discovered the ideal shape of a water clock by trial and error. In examining some ancient water clocks I notice the shape is different depending on the size. For example, a ...
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1answer
29 views

Without knowing fluid density, can it be correctly determined by measuring both kinematic and dynamic viscosity directly?

Without knowing a fluid's density, can its density be correctly determined by measuring both kinematic and dynamic viscosity directly, and then dividing these values? Can one determine cStokes and ...
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1answer
92 views

Can dynamic viscosity be measured directly and without knowing fluid density?

Can dynamic viscosity be measured directly and without knowing fluid density? If so, how? My understanding is that only the kinematic viscosity can be measured directly (with the devices that I am ...
3
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1answer
392 views

Lifting a wet object off a table

When there is a film of water in between an object and the tabletop it rests on, it is difficult to pull the object directly upward. However, when you slide the object, it comes off easily. What is ...
3
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1answer
204 views

What is the difference between agglomeration and aggregation of nanoparticles?

I've been working with colloidal nanoparticles. Most of papers are about nanoparticles' aggregation while most of people I know use the term "agglomeration". Reading wikipedia convinced me that both ...
0
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1answer
46 views

How long it takes till the gas reservoir is empty?

We have a gas reservoir of internal pressure $p$ filled with an ideal gas of volume $V$. The gas is leaking to outer atmosphere till the internal pressure equals atmospheric pressure $p_0$. The ...
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1answer
39 views

Karhunen-Loeve transform of a repeating process

This question is inspired by measurements of an unsteady flow. I have some doubts about interpretation of principal component transform using Karhunen-Loeve theorem. I have (centered $\equiv$ zero ...
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1answer
116 views

What shape is a vortex?

When I see a whirlpool form around the drain in my tub, or see a hurricane on the radar, to my naked eye it looks pretty much circular from above. Is it a perfect circle? An ellipse? If not, ...
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0answers
62 views

How does an anti-g overall work?

Assuming that a human being would be exposed by 10g in a jetplane. This g-force will cause health risks without a proper g-protection. But with an anti-g vest such health risks can be minimized. One ...
0
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1answer
82 views

Reconciling $Q=PR$ and $Q=vA$

Say we have a closed loop system, where the flow $Q$ is constant through a pipe. Then, at one segment of the pipe, we make the radius smaller. This causes the resistance $R$ to be greater, so the ...
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2answers
124 views

How to move a bubble which is trapped by the capillary pressure?

I have a question about how to move a trapped bubble in a tube. If we assume to have a horizontal tube, with water on each side of the bubble. The point to the left of the bubble is point 1, while ...
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1answer
108 views

Using water pressure as pushing force in a floating bath tub? [closed]

Does physics allow for water pressure to work in this way? if so What formula can prove this? (backup link 1, backup link 2)
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1answer
26 views

Hot water tank elements [closed]

In a 2 element hot water tank, is there a kilowatt power usage increase if only one heating element is operating correctly?