Tagged Questions

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

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SU(2) critical point and volume dependence

I am doing multi-dimensional plots of $\beta_j$ for SU(2) for infinite volume to understand the flow behavior and I was wondering, before I go too much further, if anyone knew off the top of their ...
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Origin of spin and direction in the magnus effect

If you solve the Bernoulli equation: $$p=p_0-\rho_0{v^2 \over 2}$$ using a complex flow potential for a flow around a cylinder: $$W(z)=v_0 z + {v_0 R^2 \over z} - {\Gamma \over 2 \pi } \ln(z)$$ you ...
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Angular momentum transfer in a bottle vortex

A colleague and I were discussing the following fluid mechanics experiment, which most people have probably tried in their kitchen: take a bottle full of water (a 2-litre transparent soda pop bottle ...
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Molecular structure correction factor in Mass Flow Controller

This question concerns device called Mass Flow Controller (or Mass Flow Meter). For a video explaining the principle: see https://www.youtube.com/watch?v=G62ma2IFh9o These devices are factory ...
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Modeling Syringes e.g. with the ideal gas law

Gentlemen I have a similar yet very practical problem that might provide further insight. I'm trying to model a moving plunger in a syringe (something like a piston in a cylinder). At time zero the ...
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Contraction and expansion after constricting flow though a pipe

If an orifice is placed inside a pipe with a smaller diameter than the rest of the pipe, fluid will follow a curved path in order to enter the orifice, and then expand. I was wondering at what ...
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Centrifugal Compressor Flow Rate

For a centrifugal compressor, as found in most turbochargers on internal combustion engines, is there a noticeable change in flow rate versus a naturally aspirated flow rate? In other words, does the ...
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Modelling a flow due to an oscillating hemisphere?

Say I have a long cylinder filled with air, closed at one end and open at the other. Now say I place a compressible hemisphere at the closed end and make it oscillate (compression and expansion of the ...
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Calculating optimal heat dissipation/air-flow out-of/into an enclosure - hole size vs number of holes

I am not sure if this is the right place to ask, but I figured it would be a physics question. Essentially I have an enclosure that I will be using to house the components to build a computer. I am ...
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Isentropic flow through nozzle

I've a question concerning the use of the Bernoulli principle. Let's say I have a pipe filled with air at atmospheric pressure, with a constricting section ala the figure below. The volume before the ...
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Calculating mass flow rate, force of thrust produced compressed air discharge

This one's a bit of a doozy, so please feel free to comment on any one single part or parts to this physics problem. The setup is simple--I have a container (an empty bottle) which I fill with a ...
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Reactor opening and total time to reach a specific temperature

Let's say I have a reactor (we assume that its shape can be approximated by a horizontal cylinder) in which there is air at the temperature of 1000K and at pressure of 1.5 bar. Now, I want to open it ...
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Drag Force on a cylinder with its long axis aligned with the flow

yesterday I started looking into equations that link a cylinders diameter $r$ and length $L$ to the force experienced in a highly viscous medium ($Re<<1$). I found the onseen-approximation but ...
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On deriving a fluid flow pressure drop model using either physical theory or empirical methods

I'm trying to derive a model from physical principles of fluid flow, a simple quadratic model that tends to well fit actual pressure-flow data. For (real) subsonic air flow (ideally adiabatic) ...
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Connection between gas flow rate and diameter of tubing

First time poster, long time troller and curious student. I have a bit of a conundrum that I would love some input on... Here's the problem. I have an air flow system is under constant pressure of ....
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Internal pipe flow - Pressure Drop

Let's say I have internal flow at some flow rate in a pipe that is 10 ft long and there are 2 straight sections and 2 bends. I am trying to determine pressure drop due to friction in the pipe. My ...
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Books on experimental methods, fluid mechanics related

I need some good books on experimental methods, requirements are: Fluid mechanics related; Thermal, multi-phase etc. topics should be covered; Traditional methods are good, but it would be greater ...
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Home experiment with airfoils and Reynold's number

I want to do an experiment about lowering the Reynolds number of an airfoil moving through air. I want to figure out how to lower the turbulence around an airfoil. So my two hypotheses to lower the ...
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For thermal mass flow measurement technologies is it necessary to measure gas pressure to determine volumetric flow rate?

Mass flow readings from thermal mass flow measurement technologies often provide output readings in volumetric units (e.g. standard liters per minute). Mathematically I can derive the volumetric flow ...
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What is “full clutching flow” in fluid-dynamics with regards venturi design?

As the title says, what is "full clutching flow" in fluid-dynamics with regards venturi design? I came across this reference a few times and can not find any further info on it, I'm currently ...
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Static,total and velocity pressure at a point

I have a past exam question that I am stuck on. $200$m$^3/s$ of air is entering a shaft of $5m$ diameter, the density is $1.18$kg/m$^3$, and I have shock loss of factor $X=.5$ I want static, ...
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Rapids in a River

Can I expect to have bigger or smaller rapids in a river that has a water level that is higher than average? I am not sure which way this would go. With the lower water, one is closer to the rocks, ...
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Speed of Water in a River

Does a river flow faster the higher the water level - or does it go at exactly the same speed? I was recently tubing in a river and the water seemed to be going faster with the water level being ...
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An equivalent for the Bernoulli equation for viscous liquids

I was wondering whether there is any equation for viscous liquids (probably derived from energy and mass conservation principles) relating the pressure, rate of volume flow, area of cross section and ...
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Formula for residence time/turnover rate with unsteady state

I'm not sure this is the correct place to ask my question... but maybe someone could still help me. I'm looking for a way to calculate the residence time/turnover rate. I have the production and ...
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Time required to fill a pipe line

This is quite embarrassing to ask, but I haven't done a fluid flow calculation in a very long time and when you don't use it, you lose it! I have a natural gas pipeline that I want to purge of air ...
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Discharge of a propeller in a yield-stress liquid

What form does the discharge stream of a propeller take in a Herschel-Bulkley fluid, chracterised by having a certain yield stress, shear between layers only occurs beyond that stress. This situation ...
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How to make an equal flow rate in 4 glass tubes with different inner diameters?

I would like to ask a question regarding a flow rate project I've been working on that required pneumatic software to solve. Unfortunately, I don't have the software, and I don't know how to control ...
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Air pressure equalisation

I'm programming a physics simulation and have the air pressure impact the movement of rigid bodies in the system. I know how to (approximately, both for simplicity and performance) specify bodies' ...
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How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...
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Are the blades of a propeller necessarily in the shape of wings or would flat blades work?

I think I have seen that airplane propellers are airfoils -- but I am not sure that flat blades would not work and if they do, how much more efficient are airfoils?
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Why is a controlled shear test compared to the natural flow?

Looking for the areas where contolled shear stress (CSS, where force is fixed while rate of deformation is measured) and controlled stress rate (CSR, where conversely the force is measured while ...
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Temperature of throttled flow

In a pipe with a throat, closed off to the left, I'm pouring in $\dot{n}$ atoms per second from the left. These atoms combine and do a chemical reaction, which releases energy. To the right, past the ...
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Should tunnel calibration factor be less than 1?

Regarding an experiment in which air is blown past a small-scale object (i.e. a cylinder) in a wind tunnel, should the tunnel calibration factor be less than 1? I couldn't find anything about this ...
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Hydraulic conductivity and flow rate

I have several sources that have the following equation relating the change of volume in a cell to the hydraulic conductivity (permeability coefficient) $L$ and pressure differential $\Delta P$:  \...
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Separation bubble in flow through a pipe bend

I understand that the separation bubble (length L) will grow with Re, as inertial forces on the fluid elements cause an adverse pressure gradient in proximity of the inner wall just downstream of the ...
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Flow in a cylindrical pipe

A cylindrical pipe is, at the left of section A, divided by a plane passing through its axis. The upper half is supplied with water at a velocity $V_1$, the lower half is supplied with water at a ...
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How to restict air flow without reducing pressure

I have a large volume of lightly pressurized air say 10000 cubic feet at 1 psi above atmospheric pressure. I want to move it to another area through a duct which is 20 in by 20 in. Airflow will be ...
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Is there a relationship between maximum flow rate of a fluid through perforations in a cavity and the flow rate of the fluid in the cavity itself?

I have a scenario where water is flowing horizontally through a (rectangular) cavity. The underside of the cavity has a set of perforations that look something like: and I need to determine the ...
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Several suction pumps connected to same air flow source in parallel, is this set up unequal?

I have some sensors with built in vacuum pumps that are open to the room exhaust. I have a single sample source (a compressed air tank, connected to a T fitting and I side stream sample from one of ...
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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 ...
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How to determine which one is dominant shear rate vs. flow rate

I have a question for the image below. Now we have a pump connecting to a votator for transferring some slurry. The pump yields a flow rate Q, and the votator yields a shear rate 𝛾. I wanna ...
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Fluid flow in porous medium with moving boundary

Everyone, I would like to numerically model axisymmetric fluid flow in a porous medium with a moving boundary, where the fluid pressure is specified on the boundary, whose radius increases with time. ...
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Force of Leaky Bucket over time

Indie Lab Procedure: I attached a cylindrical can to a force sensor. On the bottom of the can I drilled holes of various diameters. I then added a volume of water while collecting data from the force ...
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Fluid Dynamics - How does air behave out a window?

I often smoke out a window, and I know that if you're driving a car, the passing air will affect the pressure inside and "suck" out the smoke for instance. But what if you're in a window pane? I have ...
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How to calculate the depth of a flow meter so that there are no air bubbles in the stream

A mix of air and water (foam) is flowing into a tank from the left and going out to the right. To the right there is a suction pump. The tank is divided by a middle vertical wall that stretches from ...
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How do I convert pressure and flow from Imperial to metric units?

I'm not a physicist or have much experience in engineering. However, for a programming task, I need to change code that calculates "pressure, head, feet of fluid, gauge" into "meters of head, absolute"...
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Pressure profile and output of a coil heated burner

In a hot air balloon burner (and probably lots of other burners) liquid gas is passing through a heating coil before it exits at a hose. I realize that the point of having a heating coil is to ...