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Questions tagged [flow]

The motion of fluids (gases, liquids and granular material).

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12 views

Calculating the required amount of compressed air in order to achieve a desired flow rate (liquid) out of a tank [on hold]

I am working on a system that requires using compressed air to push a liquid out of a tank and through a nozzle at a constant flow rate. My question is how do I calculate how much pressurised air I ...
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35 views

Fluid Mechanics (compressible flow question) [on hold]

I am a grader for a fluid mechanics class, and have come across a problem that I don't understand the answer to, and I was hoping someone could explain it to me. I've quoted the question below. ...
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32 views

How do I calculate fluid velocity in an open channel?

I'm doing an experiment on hydraulic jumps I know my flowrate, however, I need to calculate the fluid velocity in m/s in order to be able to plug it into the equation for hydraulic jump headloss. I'...
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26 views

Fluid flow between two reservoirs [closed]

I recently encountered a question related to Bernoulli equation which left me very confused about the basic physics here. Say two reservoirs are conncected via a pipe and I want to know the flow ...
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32 views

Joukowski airfoil [closed]

how do I draw Joukowski airfoil through its points, in the SolidWork app? like this: https://en.wikipedia.org/wiki/Joukowsky_transform#/media/File:Joukowsky_transform.svg
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1answer
34 views

What's the link between Eulerian/Lagrangian approaches and macroscopic/microscopic point of view?

From what I know, in fluid dynamics, the Eulerian approach studies points that are fixed in space and time, while the Lagrangian approach studies individual particles and follows them. Is it correct ...
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1answer
92 views

Relationship Between Differentiation in Two Frames

In section 10.3 of Principles of Ideal-Fluid Aerodynamics by Karamcheti, he writes the following: $\qquad$ Denote by $K_1$ a reference frame fixed with respect to the moving body. We shall denote ...
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1answer
271 views

Why does water fall sort of helically from a cup? [duplicate]

I noticed today that if I took a glass of water and poured it out slowly (small tilt to the cup), it flowed rather smoothly, but when I increased the tilt the water flowed in a sort of helical manner, ...
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29 views

Limitation of continuity equation

Why continuity equation is not used in deriving/ finding the velocity for pitot tube where as both Continuity and Bernoulli's equation is used for deriving/ finding the velocity at throat in ...
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23 views

Gas Flow Rate and Pressure Difference

I have a pipe with two ends and on each end the pressure of the air is different. Is there any relation that can tell me the flow rate/speed of air inside the pipe because of the difference in ...
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11 views

Effect of Force(ex:Ship movement) on objects(nodes) deployed in the sea or ocean

I am looking for a mathematical model describing the motion of nodes deployed in sea due to movement of ship(a Force) or due to water current. I came across the drag equation which is used to ...
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18 views

Is it possible to equate the radius of a hole using poiseuille's law?

I want to calculate the radius of a hole from the leak rate. I have come across Poiseuille's law which includes the radius of pipe/hole. Is it possible to equate the radius of the hole from the volume ...
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1answer
41 views

Is Coefficient of viscosity frame dependent? Why/Why not?

Is Coefficient of viscosity frame dependent? Why/Why not?
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1answer
59 views

What are good textbooks or documents to learn numerical simulation about open channel flow like river flow?

I'm trying to learn about numerical simulation about river flow. The problem is I am a CFD beginner (just studied about hydraulics). So I don't know history or important topics about numerical ...
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2answers
77 views

Why is the stress tensor simplifying like this

\begin{eqnarray} \nabla \cdot \boldsymbol \tau &=& 2 \mu \nabla \cdot \boldsymbol \varepsilon\\ &=& \mu \nabla \cdot \left( \nabla\mathbf{u} + (\nabla\mathbf{u}) ^\mathrm{T} \right)\\ &...
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Maximum velocity of isentropic compression

In the isentropic compression tables, if P/Po = 0.9999, then A/A* = 57.8738. This is from the isentropic compression table found here: http://www.cchem.berkeley.edu/cbe150a/isentropic_flow.pdf Am I ...
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Finding the flow rate of a gaseous oxidizer flowing through a solid fuel (and they're combusting!)

I'm wondering, is there a way to calculate the volumetric flow rate or mass flow rate of oxygen flowing through a solid fuel (ex. paraffin wax) and combusting with it? After the combustion, the flow ...
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Water Bottle Rocket Thrust - two calculation methods not matching

I have been launching water bottle rockets with my kids and we are in the process of creating a simulation of the launch using numerical methods. I am a mechanical engineer, but fluid dynamics is not ...
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1answer
35 views

Air velocity from a 5mm pipe

At first, I will try to describe my problem. I have a compressed air at 0.4 MPa (4 bars) that goes trough a control valve and a flow meter into two 5 mm pipes. Flow meter shows the value of 200 ...
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1answer
26 views

How can the characteristic length of flows also be a measure of a fluid element?

This is how Wikipedia derives Reynolds number: $${\displaystyle {\begin{aligned}\mathrm {Re} &={\frac {\text{inertial forces}}{\text{viscous forces}}}={\frac {ma}{\tau A}}={\frac {\rho V\cdot {\...
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2answers
39 views

How are velocities defined in the usual form of the continuity equation?

Often in Physics classes we solve problems involving fluid flows in pipes. Usually they are solved by a combination of Bernoulli's law and continuity law, which states that the same volume of fluid ...
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1answer
36 views

Using height to calculate Pressure (independent variable) and Flow rate (dependent variable)?

The investigation is experimentally verifying Poiseuille's equation. The independent variable is the changing pressure and the dependent variable is flow rate. My experiment plan is having a simple ...
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3answers
91 views

Bernoulli's law for turbulent flow

Is Bernoulli's law valid for turbulent flow for a non-viscous, non-compressible, non-rotating fluid with isoentropic flow? An ideal fluid has coeffieicent of viscosity=0,which implies that it's ...
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33 views

What is the theoretical flow rate of water through a tube leaving a container?

The question comes from this image: There is a container with $h$ amount of water above a hole of diameter $r$. This hole leads to a tube that the water exits through. Using the pressure on both ...
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1answer
35 views

Hagen-Poiseuille equation

The Hagen-Poiseuille equation states that $$\Delta p = \frac{8\mu LQ}{\pi R^4}$$ where $\mu$ is the dynamic viscosity of the fluid. I'm just wondering, can the dynamic viscosity be replaced by ...
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47 views

Derivation of Stokes Formula using stream function

I need help with derivation of Stokes Formula. I have found derivation on Wikipedia (https://en.wikipedia.org/wiki/Stokes%27_law), but I don’t know how can I get from equation (1) to equation (2). How ...
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1answer
45 views

Why is the pressure difference the same for B and C?

So this is the question from brilliant.org: Which pipe (or pipes) carries water with the highest speed? The answer given was A. I picked C, the explanation wasn't clear to me. It says: The ...
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1answer
65 views

What happens during cavitation?

Cavitation is vapor bubbles and when they implode creates a shock wave, before imploding the bubble can reach temperatures of 10000k. I want to know what conditions must be met to make cavitation, ...
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1answer
25 views

What is the reason for the presence of a developing region in a boundary layer?

Why does a fluid first flow as shown in the entrance region before flowing as shown in the developed region ? In other words, why wouldn't it flow in developed region from the beginning ?
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Continuously cooling air at the entry to a vertical tube to get a denser air flow at exit

If you have a well insulated vertically aligned pipe open at the top and bottom to ambient air, and then continuously cool the air at the top entry cross-sectional diameter to create a free-falling ...
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2answers
251 views

Why do proofs of Bernoulli's equation assume that forces on opposite ends point in different directions?

I've read 4 different books and yet nobody explains why forces $F_1$ ($=p_1A_1$) and $F_2$ ($=p_2A_2$) point in different directions. Shouldn't $F_2$ point in the same direction as $v_2$? Since we'...
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1answer
89 views

Why does the “air” close or open doors?

Assume we have an empty room with two doors on the opposite sides of it. If we open one of the doors, the door on the opposite side automatically closes "harder", and if we close one of the doors the ...
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37 views

Why does the wind close doors?

Assume you have two rooms, both with holes in the wall (more commonly known as open windows), which connect each room to the exterior. The two rooms are connected, but the connection can be closed by ...
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1answer
40 views

Is there a Coandă effect outside the atmosphere?

For example, when air is blown through a spoon in the atmosphere, the air flow bends toward the spoon. People say it's the Coandă effect. So, outside the atmosphere, when we let air blow through the ...
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2answers
37 views

How to avoid water tension in a hose?

I am doing a project in which I have to flow water between two containers, which are connected at the bottom by a 1/4" hose. Remarkably, the surface water tension is such that water does not flow ...
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1answer
45 views

(SOLVED) Calculate the velocity of a gas inputted in pressure difference

I'm trying to make a generally simple calculation but I'm not sure if I'm approaching this correctly. So as I'm making assumptions solving this problem, please comment or correct me wherever I'm wrong ...
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38 views

How can you calculate the total time taken for water to completely flow out of a container given the amount of water initially in the container?

I'm doing an experiment on changing the amount of water in the container and seeing how the time is taken changes with it. The container has a little hole at the bottom where the water flows out from. ...
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3answers
170 views

Can the flow be irrotational if the viscous forces act on fluid?

I tried to answer the question only using the definitions and the Navier-Stokes equation: $$\rho \frac{Dv}{Dt} = -\nabla P +\rho g -\mu[\nabla \times(\nabla \times v)] $$ In my opinion if the ...
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1answer
47 views

Flow in parallel vertical pipes

Consider a tank open to atmospheric pressure, with a large cross-section area A1 and height H, that contains an incompressible fluid. Two vertical pipes with length H and cross-section area A2 are ...
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2answers
45 views

Does density vary with time in a steady flow?

Steady flow is defined as the type of flow where density, pressure and velocity don't change with time, as far as my understanding goes. However, in the video below, they say that the density in a ...
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1answer
30 views

Physical meaning of the convection term in the momentum equation of acoustic wave

In deriving the acoustic wave equation, the momentum equation is used. $$\frac{\partial \mathbf{u}}{\partial t}+ (\mathbf{u}\nabla)\mathbf{u}=-\frac{1}{\rho} \nabla p$$ Intuitively, the convection ...
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3answers
179 views

Conversion between Power and Flow rate of Fan taking into consideration the geometry of the fan

I need to find the relation between two properties of a fan, that is between power and flow-rate. I expect such a formula to depend on the pressure and on the geometry of the fan. I have found in ...
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1answer
72 views

Grad student needing help with a fluid mechanics issue in project

As the subject states I have hit a wall in a fluid mechanics associated problem in designing an experiment for my grad project. Long story short, I'm an engineering undergrad who got a broad ...
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1answer
96 views

Specific total enthalpy VS Specific enthalpy

What is the difference between specific enthalpy and specific total enthalpy in the context of fluid flow?
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35 views

Does laminar flow of a mixture tend to result in mass separation?

In a laminar flow regime, a fluid separates into streamlines with a parabolic flow profile. Do particles within such a flow tend to become aligned by mass (e.g. lighter molecules travelling together ...
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28 views

Most effecient negative shape to create laminar flow

I was looking at laminar flow filters to aid in my mycology work I'm doing. Most filters use an aluminum extrusion with fins. I figured the options out there are pretty expensive for what you get and ...
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52 views

Wich is the correct flow rate $Q$ solved with iterations?

I have a little question about this problem I computed the right answer this way First I applied Bernoulli between the top and the exit $$\frac{P_{t}}{\rho g}+z_{t}+\frac{v_{t}^2}{2g}-H_{1}-H_2-H_{\...
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17 views

Flow velocity ambiguity in transition region

I have calculated the following short table concerning the stationary flow of water in a 1 meter long pipe with a diameter of 16 mm and a completely smooth inner surface. The flow is driven by the ...
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0answers
15 views

$Gm/r$ in momentum equation of compressible flow for cylindrical geometry

In the case of compressible flow, due to the gravitational field, the source term added in the momentum equation (which is gravitational potential) is $Gm/r$ in the case of cylindrical geometry and $...
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1answer
30 views

Flow in bend pipe

What happens to a flow in a bent pipe of uniform cross sectional area? Will there be any change in flow velocity at the outlet? If yes, why does it happen? What happens at the bent area of the pipe? ...