Questions tagged [fluid-mechanics]

Questions relating to fluids at rest (fluid statics) or the forces and effects of fluids in motion (fluid dynamics).

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24 views

A Doublet's stream function

We were learning about superpositions of potential flows. so, $$\Psi_{doublet} = \Psi_{source} + \Psi_{sink}$$ where: $\Psi_{source} = \frac{Q'}{2\pi}\theta_1$, and $\Psi_{sink} = \frac{-Q'}{2\pi}\...
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how to find torque from force due to pressures that change as a function of z

My teacher is very strict about copying his work so I will have to explain it. We have a wall with two fluids of different constant densities and depths. The wall is 'L' long. The wall has a section ...
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does pressure in a centrifugal compressor increase along the path of the flow?

euler turbomachinery equation doesn't include a term for changes in flow area. But, an centrifugal impeller (not the volute) has increasing flow area along the path of the flow. Is the pressure ...
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Where is Wizard in Solidworks Flow simulation?

would anyone knows why my wizard in Solidworks 2016 flow simulation is missing, I am starting to learn flow simulation because of my study, I am still a beginner, I tried testing it 1 time with my ...
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1answer
32 views

What is 'wavelength' with reference to turbuence?

When reading about turbulent flows and turbulence spectrum I frequently come across the terms 'wavelength' 'wavenumber'. I understand that the energy is transferred from larger eddies to smaller ones ...
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Determining depth of flow in open channel flow

Open channel flow in a circular pipe has a maximum flow Q_max at a flow depth approximately 93.8% of the pipe diameter. Calculating flow Q from depths 92.5% and 94.9% both give the same value for Q. ...
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I cannot properly understand the “pressure” referred to in Bernoulli's Principle despite my efforts

I get that with Bernoulli's Principle an increase in area = a decrease in velocity = an increase in pressure. I also understand the concept of pressure being force per unit area. My difficulty is with ...
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28 views

Taylor Coutte Flow

I am not able to understand what will be the nature of solution between 2 coaxial rotating cylinders , when the thickness is very small . Basically in a taylor - coutte flow when the radial difference ...
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1answer
46 views

If a gas is pushed through a widening section of a pipe with a piston, will the pressure increase?

Imagine I have a section of pipe that increases in cross-section at some point. If the gas in the pipe before this section is being displaced with a piston, will the gas increase its pressure and ...
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1answer
50 views

Low maintenance device to trade flow rate for lift height?

Is there a compact device which can trade flow rate for lift height without too many moving parts? My particular application is a 10 meter deep and 10 centimeter wide well with shallow water level, ...
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1answer
23 views

Is the flow same in parallel pipes feeding into a water container?

I have 2 questions. I am aware that the headloss is the same in all intakes into a water container. My question is, is this illustration correct that the flow is different for different outlets? And ...
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What is the purpose of the ink delivery disks found in most rollerball pens

See picture. In most rollerball pens there are those peculiar looking disks near the nib, the purpose of which I have not yet figured out, apart from being some kind of ink reservoir/flow control. ...
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Hydraulic system dynamics modelling

I'm trying to mathematically model an actuation system and it comes down to relating the pressure across the pump and the actuator as shown in the picture. Assuming no friction in the pipes and the ...
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55 views

Bernoulli equation on moving cart

Let’s say I have moving cart with velocity U . And water from pipe flows at velocity V with respect to ground The question asks to use Bernoulli equation , pressure is atmospheric in the top If I use ...
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1answer
22 views

Why does this glass tend to stick on surfaces

I have a glass here. This is the bottom face of the glass. Now this is on what I had kept my glass. There is a little much of water spilled on it. Let us call this thing as C Now , when I lifted the ...
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30 views

Calculate the thrust of a fan

I'm having some difficulty with the following problem: The fan operating parameters are adjusted to reduce the constant negative pressure at the inlet ($p_\infty-\Delta p$) within a certain range of ...
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1answer
175 views

Why is the direction of pressure always perpendicular to surface area for fluids?

Why is the direction of pressure always perpendicular to surface area of a body for fluids ? We also assume that it is an ideal fluid here. So , pressure acts in all directions because fluid has a ...
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Finding all the pressure acting on base of cylidner

Water is filled in a flask up to a height of 20 cm. The bottom of the flask is circular with radius 10 cm. If the atmospheric pressure is $1.013 \times 10^5$ Pa,find total force exerted on the bottom ...
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23 views

Why is the atmospheric pressure given as the value of length of mercury column in barometer

Why is the atmospheric pressure given as the value of length of mercury column in barometer. Since the density for the both the cases are different. Is it that by experiment we found the value to be ...
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1answer
128 views

Derive a formula for the propulsion force - verification request

I'm having some difficulty with the following problem: Derive a formula for the propulsion force containing $\rho, Q,S, u$ (pic below) The propeller is moving left with the speed u. My only idea was ...
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2answers
38 views

At what negative pressure do gases separate from water?

According to this video, when a valve is quickly shut, the water hammer effect can lead to a high negative pressure in a pipe downstream. This leads to dissolved gases coming out of solution with the ...
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1answer
69 views

Is there a limit to how high a water fountain can go?

The current world record was set by King Fahd's Fountain at about 300m, and a water speed of about 375km/h. Would it be possible to launch water much higher? Say, by aiming a water jet cutter with a ...
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28 views

Pressure drop in a CFD simulation of an air flow too small

I am simulating a turbulent air flow through a rectangular channel with the goal to match measured velocity profiles and the static pressure at certain points. My problem is that the pressure drop in ...
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4answers
70 views

Can a vacuum in a room increase the pressure in a tube?

Ok, So I work as a Marine Engineer but I do not have an engineering degree so I am having a hard time wrapping my head around this problem. So currently on my ship we had a minor spill overboard from ...
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2answers
52 views

Shearing Stress at the Boundaries of two infinite Planes

This is a worked example on a book I am reading (Fundamentals of fluid Mechanics). He then asks "Can you explain the change in sign? [Hint: Sketch a sheared fluid particle adjacent to the top ...
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Is Viscosity = Slope?

studying fluid mechanics, I see that viscosity relates shear stress to shear rate, like a slope. However, on graphs I see that they draw a triangle, and where I would expect to see $\Delta \tau $, I ...
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Translations from “Oil” Flow Rate - Pressure drop to “Air” Flow Rate to Pressure Drop charts

I keep getting check-Valve companies that have their product data sheets registered in Pressure Drop-Flow Rate for oil(Hydraulic oil) and I need it for Air. Is there a translation between oil and air ...
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41 views

Extraction Fan Setup

I have recently bought myself a Flux Beamo laser cutter and am now in the process of setting up fume extraction for it to vent outside. The laser unit has a built in fan of which I haven’t been able ...
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1answer
39 views

Does air flow rate of an air pump imply the same rate when using it to pump water via air pressure?

I want to build a machine that pumps liquids (roughly density of water) out of an enclosed cannister. The cannister has for one inlet for air at the very top and has an outlet (near the top as well) ...
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18 views

Control Volume Method for Calculating Pressure Distribution in a Turbomachine

I'm looking at ways to calculate the axial thrust of a turbomachine. The ways that i've found in books aren't the best documented. I know I can't use Bernouli's law since the impeller will chop up ...
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Convergence problem in RANS simulation of unsteady flow

I am simulating an air flow through a two dimensional rectangular channel. The channel splits into two channels, one of them is followed by a 90 degree bend downwards and leads into a cylindrical ...
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67 views

Calculate fan power

I was wondering how to calculate the required fan power for the following air pipe network. Other losses besides friction is not calculated for. Known parameters: Fan provided flow, VA = 3000 m3/h ...
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Can't Find Regulator for 16G CO2 Cartridge (800 PSI to 400-200PSI)

I am trying to make a Paintball Gun that works off of 16G CO2 Cartridges(800 PSI). I can't find a compact regulator that drops 800 PSI down to 400-200 PSI. If anyone knows of such a regulator could ...
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Is it wrong to consider that these velocities are the same?

I have this simple problem and I am wondering if it's wrong to consider v1= v2 =v3 = v/3. "A" is the area. The fluid is air, I am not considering head loss. Thank you.
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Joule Thompson Effect and Isenthalpic Processes

We are trying to compute the Joule Thompson (JT) coefficient for air going through a valve from P1 to P2 (where P2 is a much lower pressure). Beginning this we were thinking that the water in the air ...
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2answers
43 views

Why does flow separation cause stall when it creates a low pressure zone?

In an airfoil, a low-pressure region forms in the turbulent wake created when the flow separates. Wouldn't this cause an increase in the net vertical force acting on the airfoil since the pressure at ...
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1answer
37 views

Quantifying the reaction force on fixed tubing connected to a peristaltic pump

I am not sure how I should consider the forces due to hydrostatic pressure when calculating the reaction force due to a fluid being pumped through fixed tubing with a peristaltic pump that I am using ...
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43 views

why LP gas tank does not provide fuel when the pressure reaches 10%? And to to resolve the issue?

I am having this problem that some LPG tanks don't provide fuel and other does.. I was told that the problem is whenever the ambient temperature is low (so is the gas), the pressure drops as well and ...
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20 views

Air flow optimization in a small opening

I have a 36 x 6 cm opening from where I need to pull fresh air. I need to optimize for air flow as well as noise. I considered using 6 Noctua NF-A6x25 fans which would give me a total of 175,2 m3/h at ...
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26 views

How could an absorbent material be emptied?

I have been thinking about this for quite some time: Given a foam or other absorbent material saturated with a solvent, how could you draw all the solvent to the top of the foam (basically how could ...
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Navier-Stokes with non-newtonian fluids

So I've got a problem here in fluids. It's driving me insane but I know I'm missing something simple. Up until now we've worked with Newtonian fluids resulting in the "normal" NS equations ...
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Blade efficiency of a franscis turbine

The blade efficiency of a turbine is defined as the ratio of the power extracted from the fluid by the rotor to the power available at the inlet of the rotor. The power available at the inlet of the ...
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2answers
42 views

Sunlight-powered device set to change world: will it work? [closed]

Vast areas of desert sand are being shone on upon by the sun. Now that's some ENERGY! Using this proposed apparatus: Sunlight over large area is concentrated on steam chamber, where water turns into ...
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How to Derive the Differential Form of the Contintuity Equation

The book "Gas Turbine Engineering Handbook" by Boyce, on p. 117 states, the continuity equation, $ \dot m = \rho A V $, has as its differential form, $ 0 = \frac{d\rho}{\rho} + \frac{dA}{A} ...
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Understanding Stagnation Pressure Head in non-compressible fluids

Does the stagnation pressure head in a pitot tube allow for the calculation of dynamic head at a point in the tube, given that the static pressure head at the point is known? For example in the ...
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Explain pressures created by fluid flow through small orifices

So my question is in relation to fluid flow and pressure. In my pictures below you can see that i have two similar situations. Fluid flows in from a large reservoir at a constant rate through a ...
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Can you shape a buoyant object stuck to the bottom of a body of water such that it floats?

I understand that an object, say a closed plastic cube full of air, stuck to the bottom of an aquarium with a smooth glass bottom will not float if you firmly place it such that no water can get ...
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41 views

Is there a valve design or system that can do this?

I am trying to come up with a way to bleed air from a tube to avoid air (gas) from reaching the other end of the tube. Is there a way to do this automatically? It must be able to work in all ...
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1answer
31 views

How to make a 500+ psi water gun staff

I would like to create a life size lego Bionicle Aqua axe(gali nuva Type or gali master of water Type). The problem is unlike The trident in this video: https://m.youtube.com/watch?v=NK6MWt7vpVE&t=...
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What is the use of streamlines in Fluid Mechanics when velocity fields seem sufficient?

So, streamlines are a family of curves which, for every instant in time, are the velocity field envelops. And in general, envelopes of a vector field are the curves whose tangent vector at each point ...

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