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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Handling the source term in the convection-reaction-diffusion equation

The 1D convection-reaction-diffusion equation for solute transport is given as: where C is the concentration, v is the flow velocity, D is the diffusion coefficient, S is the source/sink term, and R ...
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Conceptual explanation for subsonic nozzle VS supersonic nozzle

A nozzle is a device that increases the velocity of a fluid in the expense of pressure energy drop of the fluid (The Bernoulli principle). Now how can we explain (conceptually, no math) why a subsonic ...
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What is substance of this situation? Is this Dean Vortex?

https://www.youtube.com/watch?v=2k4Rf_UAifg&t=488s You can see there is a vortex in miter bend. Is that a Dean vortex? But Dean vortex that I've known is pair vortex. But in this video there is ...
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Arclength of a pipe length between two different elevations [closed]

I am trying to find the arclength and max height of a pipe between two reservoirs A and B. The height of A is 0.4km and the height of B is 0.6km. The change in elevation is given by $z^* = a + bx^* + ...
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Derive the governing differential equations for fluid velocity if the fluid is an incompressible Newtonian fluid

Derive the governing differential equations in three dimensions for fluid velocity if the fluid is an incompressible Newtonian fluid with the following constitutive relations: constitutive ...
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How to determine pump input/output pressure?

I wanna create iterative simulation of some fluids system. In this system i have multiple connected objects. For each object i calculate input and output pressure and then calculate transfered amount ...
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84 views

Why flow around an airplane is different in different frames of reference

In the book Fluid Mechanics by Yunus Cengel it was written "Flow around an airplane, for example, is always unsteady with respect to the ground, but it is steady with respect to a frame of ...
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Resultant hydrostatic force on a gate for a fluid that doesn’t reach its center of gravity

Forgive me for these drawings, I can't think of a better way to illustrate the problem right now. When looking for the resultant hydrostatic force on a flat surface, we can use the formula $F = PA$: ...
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How much longer could Titanic have remained afloat if it had gotten rid of its anchor and chain right after hitting the iceberg?

I am wondering how much longer the RMS Titanic could have remained afloat if the crew had allowed the ship's anchor and anchor chain to fall to the bottom of the ocean immediately after the ship had ...
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Static pressure in a free jet

If I have a free jet that is subsonic, say simply the exhaust of a hair drier (operating with no heat), how does the jet pressure vary longitudinally along its axis, as it decelerates from moving to ...
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What is the reason for forbidding liquids for cooling in drilling on cfrp/Al or cfrp/Ti stacks?

I recently did some research on the effect of cooling on CFRP/Al7075 drilling.But I read somewhere that liquids are forbidden for cooling operations on these multi layer plates !!! , And I wanted to ...
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Are there nozzles with non-varying cross sections?

I'm scouting some nozzles to fill in gas into a chamber. To get a better understanding of nozzles in general, I'm reading https://en.wikipedia.org/wiki/Nozzle and I stumble already on the second ...
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The differential height of the manometer and the force needed to hold the container in place are to be determined

A cylindrical container equipped with a manometer is inverted and pressed into water. The differential height of the manometer and the force needed to hold the container in place are to be determined ...
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Confusion between Steady flow and Space-Time invariant density field

Let's take the example of a steady flow with velocity field as $u=βr(\tilde{r})$. Now, we can find a density field $ρ(r,t)$ that satisfies the mass conservation equation of $∂ρ/∂t+∇(ρu)=0$. First, ...
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Pre requisites for a course in Heat Transfer from Fluid Mechanics , for a Mechanical Engineering Bachelors Degree [closed]

Can anyone please tell me the topics I need to study from Fluid Mechanics, specially fluid dynamics to understand Heat Transfer in a better way?
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Efflux velocity for system with air and liquid

I want to calculate the efflux velocity for this open vessel with area $A_1$ with a small outlet with area $A_2$ as a function of time. The atmospheric pressure is $p_0$. The vessel has height $h = h_{...
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Valve solution for mixing external air into a closed loop climate controlled air circulation system

I'm looking for an electronically controlled air valve solution which would provide a way to mix external air into a closed loop air circulation system used for climate control in an enclosure. The ...
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Using venturi effect for equilibrating pressure drop

Let me first say I am a novice in fluid dynamics, I am not sure about terminology but I will try to explain myself as clearly as possible. I need some help for understanding the following case: in a ...
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How to simulate gas-liquid mixing in a bioreactor in ANSYS Fluent?

I thank you for taking a look. I'm a beginner with so much love to simulate fluids as fluid visualizations fascinate me. My learning has been only through youtube, forums. So, please excuse my naivety ...
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Can I create a whirlpool/vortex around a horizontal axis in a flat bottle using motor?

I am using this flat bottle: I fixed a motor at the centre of one of the flat sides and attached an impeller. I thought this will create some kind of whirlpool effect but as you can guess, since the ...
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2answers
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Why is the theoretical formulation not explaining why the graph of the square of the velocity and angular displacement is nonlinear (experimentally)?

So I did a wind tunnel experiment where I put a rope restrained (1 degree of freedom, so it can wave in the direction of the wind) at one end so that it displaces according to the variation in wind ...
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Frictionless flow in pipes

I am trying to understand the flow of an ideal, frictionless incompressible fluid through a pipe for these two cases. Note: Please consider Flow velocity in the tank is zero, and the fluid is ...
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How do you imagine momentum?

If you want to explain it to a layman (who belongs to the science stream ofc!!) how do you explain it? Also, what is momentum transfer when it comes to fluid mechanics?
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61 views

How does shear/viscous stress change in liquids as applied shear force is changed?

As per Newton's law of viscosity, the dynamic viscosity of a Newtonian fluid is constant (doesn't change with applied shear stress).Consider the Couette flow used to explain viscosity . Whenever we ...
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Watering utility that does not spill

I saw a video showing a water bowl for a cat that used an upside down PET bottle to provide "fresh" water when cats consume some of the water in the bowl. I wanted to design something ...
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1answer
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How to select a fan blade for my application (strong, focused breeze)

My question is how fan blade design relates to the focus of the air leaving the fan. I am looking to generate the most focused breeze I can with a fan blade, excluding additional ducting etc, the fan ...
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What is the velocity of a fluid particle at the center of a infinitely long counter-rotating vortex pair?

Let's take circulation strength of each vortex τ and distance between them is r. I feel the answer should be 2τ/πr but my friend is arguing its τ/2πr. So my thought process goes like, if you have a ...
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Water fountain laminar flow options using a 3d printer - can the default be significantly improved on?

I don't know if this is the right place to ask, but it is the best I can find! Laminar flow from a garden hose: All of the YouTube DIYs show a PVC pipe with the same sequence: Some sort of evener-...
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1answer
56 views

How to calculate head loss in vertical pipe?

I have used the Hazen-Williams equation to calculate head loss for falling water in a vertical pipe I am using in a hydroelectricity project of mine. Hazen-Williams equation: These are the properties ...
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1answer
104 views

Pipe network analysis: static pressure of a closed-loop pipe

I've learned fluid dynamics but does not have much knowledge about its real-world applications. My question is about the static pressure of a closed-loop pipe. [Fig. 1. Pipe network. Source: ...
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Is this value of critical Reynolds number also valid for ducts?

In internal flow, when a fluid flows inside a circular pipe, the most practical value of critical Reynolds number is taken as 2300. I was wondering if this number is also the same for non circular ...
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Fluid Dynamics - Auto filling a reservoir to a constant water-level

I have created a reservoir that is intended to automatically self-fill at exactly 1/4" depth. The idea is that the reservoir is hooked up to the airtight jug and dispenses the liquid until the ...
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Why is a throttling valve isenthalpic whilst a nozzle is not?

From my understanding, Nozzle's and throttling valve are devices which both trade pressure for velocity, so they increase velocity at the expense of having to decrease the pressure. If we examine ...
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Is Bernoulli’s equation applicable for systems with pumps?

Please have patience with me as I have not looked at this sort of theory in many years (I am also very new to StackExchange). A question asks the following: A sloping swimming pool two-thirds full of ...
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1answer
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How to mix pure CO2 with air so that a bioreactor can be fed with air at 0.1% to 10% CO2?

The situation is we have to prepare a gas mix of air and CO2 which has to be given as input from 0.1% to 10% CO2 of air mix to the aqueous medium in a bioreactor? I'm trying to build a simple and ...
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4answers
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Balancing suction air flow at different areas on pipe

I have a T-shaped pipe that is connected to a vacuum pump. Along one side, there are 4 areas of 9 holes where air will get sucked in from the surroundings. It's used to pick up some small objects. The ...
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How can I make a vacuum pump to move rocks from one place to another?

I am trying to build a vacuum pump by myself and move rocks from one place to another. After some online search, I came across this video on Youtube. I am trying to build something like this. Can ...
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1answer
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Is a no-moving-parts air pressure transformer possible?

Is it possible to construct a solid state fluid system (tubing, channels, chambers, nozzles, etc.) that can convert the energy from a low-pressure high-flow-rate air current into a high-pressure low-...
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Book recommendation for hydrodynamics of bubbles, drops, and particles

I am wondering if someone could please recommend to me some references on the topic of hydrodynamics of bubbles, drops, and particles, preferably in the context of complex and bio fluids. I am ...
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Is NPSHr dependant on temperature?

I know that net positive suction head available depends on temperature since viscosity, density and vapour pressure depends on temperature but how about NPSHr? We know that the vapour pressure depends ...
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2answers
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Can I dismiss wind loads for this solar panel configuration?

I asked this question before in the Physics Stack Exchange, but it was closed because it was considered being about engineering. That is why I am asking it here. I am planning to install some solar ...
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1answer
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Need help on conservation of momentum (liquid jet) Problem!

I had a quick question regarding this homework problem, I can't seem to understand why they chose to use the conservation of momentum in vertical direction and not the horizontal direction as you ...
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1answer
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Analytical solution for the 1D convection-diffusion equation

The Ogata and Banks analytical solution of the convection-diffusion equation for a continuous source of infinite duration and a 1D domain: where C [mol/L] is the ...
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Non-Dimensionalizing Navier-Stokes equation to derive the Thin-Film Equation

I want to start with the general Navier-Stokes equation in 3-D: $$ \frac{\partial \vec{u}}{\partial t} + (\vec{u}\cdot\nabla)\vec{u}=-\frac{1}{\rho}\nabla p+\frac{\mu}{\rho}\nabla^2\vec{u}+g\sin{\...
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What is a safe and efficient temperature range for absorption chiller generators?

I've read that the role generators play in the absorption chiller cycle is to concentrate the salt solution so that the evaporator/absorber can maintain a vacuum by constant absorption of vapour ...
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How Do I Calculate the Velocity of the Flow That Is Sucked Into Two Parallel Walls by a Fast Moving Flow?

I'm trying to solve a problem where I calculate the velocity of the setup bellow. Basically I have two very long(basically infinite for calculation purposes) plates, and I have one central jet of gas ...
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92 views

In which bucket , should the water fill it up first?

Here , we have two water filters and buckets . Now , we know that as the water falls down , it’s speed increases because of acceleration due to gravity. Let us say I started both the filters and once ...
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1answer
59 views

Angular Velocity And Flow Rate Relationship Of Turbine

I was designing a turbine to be utilized in order to measure the flow rate of a river system. I can measure the angular velocity of the shaft by utilizing a magnet and hall sensor, however, in order ...
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Given flow rate of an orifice at one pressure, how do I calculate flow rate for a different pressure?

Given an orifice rated 1.8 GPM of water at 90 PSI, how do I calculate the flow rate at 30 PSI and what rating I would need to purchase to achieve 1.8 GPM at 30 PSI? Below added to give some context, ...
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Stokes Number (characteristic length)

I am working with a high speed flow that is non-stokesian, but that isn't the issue. There are correction factors for that. I am attempting to figure out what value to use for the "characteristic ...

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