# 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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### System curve for use in determining pump operating point

What is meant by a "system curve" that is used to determine the operating point of a pump. I know what a "pump curve" is, but I often hear about a "system curve" being generated so that the pump ...
244k views

### How to calculate flow rate of water through a pipe?

If a water pipe is 15 mm diameter and the water pressure is 3 bar, assuming the pipe is open ended, is it possible to calculate the flow rate or water velocity in the pipe? Most of the calculations I ...
46k views

### How to determine the characteristic length in reynolds number calculations in general?

I understand that the reynolds number is given by the expression $Re=\frac{\rho v L}{\mu}$, where $\rho$ is the density, $v$ is the fluid velocity and $\mu$ is the dynamic viscosity. For any given ...
7k views

### How Can I Determine Multiple Discharges from a Pipe Network? (Knowing the Inlet Conditions)

I have little/no experience with pipe networks and have been searching for a methodology to calculate the discharge from multiple outlets of an oil pipe network with a single inlet. As far as i can ...
3k views

### How an airfoil works

I have read on many sites that for lift to occur, the pressure below a wing must be higher than the pressure above it. This happens by somehow moving air faster over the top of the air foil so the ...
156 views

### Formula to describe flow over thin weir

I have thin weir, really just a sheet of metal with a smooth and straight upper edge. I want to know how much water will flow over this weir, when the water level on the higher side is a few cm above ...
90 views

### Will high velocity air directed underneath a half-toroid shaped Coanda saucer by a centrifugal impeller create a lifting force?

I would like to know if a lifting force will be created by the Coanda effect from high velocity air that is directed underneath a half-toroid shaped saucer by a centrifugal impeller. I am seeking an ...
3k views

### What's the maximum water jet psi we can create?

Hy everyone, new here, I don't know much about how high pressure water pumping works - ( i'm just a programmer ) but i need to know if we can create water pressures ...
320 views

### Is radians a dimensionless quantity?

Quite often while calculating angular velocity we come across the quantity radians per second. How do I treat radian dimensionally?
197 views

### Which components to use for a CO2 gas storage?

I have a CO2 production for my aquariums (currently 2, but the solution should be extenable to - let's say - 5) based on fermentation of bio mass (CO2 is used as fertilizer there) which consist of a ...
97 views

### Calculating Minimum Pipe Pressure Requirement for an Irrigation System

I am setting up an irrigation system for my ranch and I have a hard time calculating the minimum pipe pressure requirements to reduce cost. I need to know the maximum pressure the pipe has to cope ...
62 views

### producing vibration motion of a plate (1cmx2cm) placed in water

In order to conduct a study, I need to place a rectangular plate freely placed (1 cm by 2cm) inside water and control it from outside (better wireless). I need to give oscillatory motion with specific ...
50 views

### what should be the size of gate? [closed]

what should be the size of gate? if street 8 ft according to house map Car entrance gate 11 ft can corolla grande car enter into the gate easily with some moves?
7k views

### Is it possible to build an air compressor with no moving parts?

Is it physically possible to build an air compressor with no moving parts? I'm envisioning a thermodynamic cycle capable of compressing air with no moving parts and operated in a stationary way. There ...
1k views

### How to know whether the flow is supersonic in a nozzle?

For a project I had built a convergent divergent nozzle designed for Mach number = 3. In that project, I could know the flow has gone supersonic by seeing the manometer fixed between the throat and ...
672 views

### efficiency and flow separation

I am studying about wind turbine and turbine. I have some questions, but first, I explain some cases as follow: Low velocity air over an airfoil at a zero-incidence angle does not initiate flow ...
534 views

### How is gas flow through (extremely long) pipelines monitored and controlled?

(This is closely linked with measuring the Mach number inside a nozzle but it is not regarding the supersonic flow) Friction and heat transfer have effects on the Mach number of the compressible flow ...
6k views

### What makes the material travel through Archimedes' Screw?

...or in other words, why doesn't the material just stick to the screw, rotating in place, without progressing along its length? In the simplest case, the answer is obvious: gravity. If it's a ...
108 views

### Equating $\frac{dp}{dt}$ and $F$ at a hydraulic jump?

A journal I am reading about circular hydraulic jumps provides the equation and I quote: $H$ Depth after hydraulic jump, $h$ depth before hydraulic jump, $V$ velocity after hydraulic jump, $v$ ...
977 views

### Estimating Maximum Speed for a Pneumatic Cylinder

I am designing an machine that is going to use a pneumatic cylinder to accelerate a projectile. I have a tentative cylinder specified, and am working on the control and supply side. I have verified ...
480 views

### Fluid mechanics - how to calculate flow distribution in piping network?

I am trying to build flexible, visual tool to calculate flow distribution through the piping network (mobile hydraulics). I have root node of the network which has defined flow and pressure inputs. ...
3k views

### Losses through holes drilled in a pipe

I asked a previous question about pipe t-junctions with pipes of varying diameters, and it got me wondering... How are losses handled and calculated in pipes with holes drilled directly into them? ...
129 views

### How can I make an uncalibrated flow meter for water flows of a few liters per hour

Or alternately what is the name of the device I'm looking for? My first thought is to make a narrow V shaped chamber by gluing 1/4" acrylic together with 2 face plates and a mid plate with a ...
397 views

### what's the best shape for inducing condensation?

What would be the best ceiling shape for inducing condensation? I'm guessing it would a curve ︶ or V shape, but those are just guesses. (I don't have any background on thermal physics)
592 views

### Flow in a T-Junction with pipes of different diameters

I have been trying to model a complex pipe network recently and have come across something I can't find any information on. In my model, I have been assigning equivalent lengths of pipe to various ...
1k views

### Whistle Design - Optimizing sound initiation pressure and volume

Assume you can use any whistle type, is there a way to choose the pressure point at which a whistle makes noise? For example I have a whistle that starts making noise at 2 psi but I would like to ...
6k views

### How to prevent deposition of dust on ceiling fan blades

It is well known that dust gets deposited on a rotating ceiling fan because formation of a boundary layer over fan blades. The air layer next to blade surface is stagnant due to no-slip condition and ...
2k views

### Contours of radial-flow impeller vane

I've been studying the design of turbopumps and their impellers, all the design equations and what-not; this question concerns the contours of the impeller vanes. I'm going to attempt to enter ...
557 views

### Incompressible 2D pressure-driven flow: for Navier-Stokes equations in nondimensional form, how should I express pressure boundary conditions?

*I have updated this question. I'm using two codes for modeling incompressible, two-dimensional flow out of a tank. My fluid dynamics experience is pretty basic; I'm using the codes to understand a ...
159 views

### Multiphase Flow - Energy Coupling Parameter

I have a general question regarding energy coupling in multi phase flow. My question comes is based on the text from this book: https://books.google.co.uk/books?id=CioXotlGMiYC&pg=PA33&lpg=...
348 views

### Why does the standard $k-\epsilon$ model use zero equation models?

According to Hoffman, the standard $k-\epsilon$ turbulence model incorporates a two-layer approach (inner region and outer region formulations to reperesent mixing length) when it comes to regions ...
2k views

### What does 'Open Flow' mean for a pump flow rate?

I have specifications for a positive displacement pump where, in the data table on the last page, the given flow rate is referred to in the column header as 'Open Flow.' Is this the maximum flow ...
1k views

### How does the pressurized suspension of the Hyperloop not affect the tube pressure?

So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurized air cushions. These cushions lift (or at least help lift) the capsule and reduce drag ...
6k views

### Determining mass flow rate and exit velocity of compressible flow

This one's a bit of a doozy, so please feel free to comment on any one single part or parts to this problem. The setup is simple--I have a container (an empty bottle) which I fill with a certain ...
32 views

### Is there a (sort of inverse security) valve which opens if one connected side has a pressure below a certain value?

Security valves with two connectors open if the pressure exceed a value x +/- tolerance on one side. I'd like to know if there's a mechanical valve which opens if the pressure on one side sinks below ...
172 views

### Why textbooks use geometric center/centerline of the pipe when calculating/measuring pressure?

Studying Fluid Mechanics, I started to notice that almost every textbook/website uses a specific point to make calculations about the pressure in a liquid at a given depth (hydrostatic pressure): the ...
1k views

### How to calculate required air mass flow to keep CPU below certain temperature?

I have been assigned to work out how much air flow is needed through each partition of our servers in order to keep our processors at (or below) 60C (333K). I have worked out the current mass flow ...
4k views

### X-form and cross-form rudders in underwater control

What are the advantages of using X-form rudders in comparison to cross-form rudders? Why do some submarines, torpedos and underwater autonomous vehicles use X-stern control? X-stern: Cross-form:
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### Force applied by fan under inviscid & incompressible flow

I have a wind tunnel (subsonic flow of air) which consists of a fan inside (and ahead of) a long cylinder of cross-sectional area of $A_e$, followed by a diffuser of $A_o$ c.s. area ($A_o>A_e$). ...
146 views

### Can the continuity equation and Bernoulli contradict each other?

Please bear with me - I'm a lapsed mathematician and I'm self-studying these concepts. A question asks the following: Water flows in a pipe of diameter 5 m at a velocity of 10 m/s. It then flows ...
942 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 ...
54 views

### Why does higher concentration of electonic components decrease the airflow requirement for cooling a PC system?

This source describes in detail a formula used to calculate the airflow requirement in order to cool a computer system. $$Q = \dfrac{P_{loss}}{c_p \cdot \rho \cdot \Delta T}\cdot k$$ Clearly, the ...
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### Relative improvement in flow from diameter change with sub-milliimeter tubing

I want to calculate the improvement in flow rate that can be achieved with changing the tubing size when the tubing is sub-millimeter size. I originally approached this using a simplification of ...
79 views

### How to calculate heat and mass transfer rates from an enclosed box?

I'd like to know if it's possible to calculate the heat and mass transfer rates from a small volume to the environment. Let's assume there is a box with a small opening at the top. The air inside the ...
43 views

### Normal Shockwaves occurrence at cone tip with Angle Theta

I have a question regarding shockwaves. So as far as my knowledge, a flow moving at Ma= 1 will create a normal shockwave ($arcsin(1/Ma)$) , and a flow moving faster will cause an oblique shockwave. So ...
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### Energy calculations for steam turbine

I am a civil engineering undergraduate. I have an interest in Biotropic Design and sustainable energy and am working on a new conceptual design. I would like to know what analytics may be done to ...
50 views

### What changes can be made to a whistle to change these variables? [closed]

I have read that the longer the whistle the lower the pitch and the shorter the whistle the higher the pitch. But there are other factors. Pressure, size of the inlet, size of the outlet, diameter of ...
313 views

### Easy model to calculate water flow rate over trough ledge?

Trough is 1.87 meters long and 0.5 meter wide and 0.22 meter deep. Water only flows over the 1.87 meter long side and from both sides (so x2). The water overflow is 0.012 meters tall (ruler ...