All Questions
7,190 questions
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From material derivatives to partial derivatives in the wave equation
Consider the Cauchy momentum equation:
$$\rho \frac{d^2 \mathbf{u}}{d t^2} = \nabla \cdot \boldsymbol{\sigma} + \rho \mathbf{f}$$
where $\rho(\mathbf{x},t)$ is the density, $\mathbf{u}(\mathbf{x},t)$ ...
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Lattice Boltzmann Methods
I'm reading an article from Shiyi Chen et.al named "On boundary conditions in lattice Boltzmann methods". In the first section they proceed to the well known Chapman-Enskog expansion in ...
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24
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Questions on surface tension
I've learned that surface tension occurs due to the difference between the molecules of surface and the bulk molecules and the asymmetry between them. The particles next to the walls of the container ...
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1
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1
answer
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'Physics behind the morphology of clouds' book recommendations?
Clouds are a wonderful and fascinating tracer of atmospheric motions, and I keep wondering if there's a textbook/popular science book out there that focuses on explaining the atmospheric dynamics/ ...
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1
answer
28
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Ideal fluid flow in a frictionless pipe at same horizontal level
Assume ideal fluid in a frictionless pipe at same horizontal level. If we apply an external force and then remove it.
1.Will the fluid keep flowing with the same velocity?
What is meant by pressure ...
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35
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What is meant by fluid pressure?
I understand that fluid pressure means the pressure the fluid exerts on some surface, but what surface are we talking about? Is it the force exerted on tubing or the fluid itself or are these both the ...
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1
answer
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Can the irrotational vortex be described using spherical harmonics?
THE BACKGROUND:
The irrotational vortex is an ideal fluid flow that can be represented via the following expressions in cylindrical $\{R,\psi,z\}$ and spherical $\{r,\theta,\varphi\}$ coordinates:
$$\...
- 3,267
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How to use Bernoulli Equation in a rotating reference frame in this problem? [closed]
I've been trying to think how can we use the value of pressure to find the inlet flow rate because I don't see another use for that value and I believe they have to be relate because of conservation ...
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answer
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Why do we include both local and temporal acceleration in fluid mechanics but only consider temporal acceleration in solid-body mechanics?
I am a beginner in physics, and I was studying fluid mechanics, specifically Newton's second law, when I was surprised to find that the expression for acceleration was composed of both local and ...
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How Dump Tubes (arrangement with lot of perforation) reduces the pressure of Steam flow. How to derive a scientific basis of designing a dump tube [closed]
Recently I have come across simple yet intriguing device - The steam dump pipe with multiple perforations (orifices).
The dump pipe is typically used to reduce the steam flow pressure. The inlet steam ...
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answer
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Reynolds Transport Theorem in a Non-deforming Control Volume Moving At a constant velocity [closed]
Question: In this problem do I have to use Bernoulli's equation to find the velocities in sections 2,3 and 4? and I want to know that can I assume that the flow is uniform.
Edit: I'm not looking for ...
2
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2
answers
71
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While crossing a river should we cross it at wider regions or narrower region? [closed]
I know that in wider regions velocity of river is less than that in narrower region. This suggests that we should cross the river at the wider region. But at wider regions pressure is more due to the ...
user366132
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76
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Has low pressure been generated in the open space of this device?
A represents the left and right speakers, B represents the left and right baffles, C represents the rectangular holes on the left and right baffles through which the sound waves from the speakers can ...
- 2,165
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answers
36
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Can a window fan keep heat indoors? [closed]
Can a window fan keep heat indoors when it is colder outside than inside? Suppose a window with 1 unit of area must be open. If the goal is to decrease the rate at which the inside / outside ...
- 121
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1
answer
32
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Hydrostatic equilibrium and fluid velocity
If we consider a fluid with velocity $\vec{u}_0 = u_0 \hat{x} + v_0 \hat{z}$ which is now in hydrostatic equilibrium.
I know that the force associated to the gravity and force associated with the the ...
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56
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Determine the maximum and minimum acceleration from the velocity field [closed]
If the speed distribution, in m/s, of a flow is given by $v = 2x^3 + 2y^2 - 3z$, then the acceleration of the fluid at the point with coordinates $[2, 1, 5]$, in meters, will be greater than $20, \...
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56
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Forces on a 18th century ship [closed]
I am trying to make a 18th century ship simulation where the ships are moved by the aerodynamic forces in their sails and the hydrodynamic forces on their hulls. The simulation is in 2D, so I ignore ...
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1
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36
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Potential flow over a sphere in circular motion
The potential for a sphere moving in a straight line with a constant velocity U in an incompressible, inviscid and irrotational fluid is given by the following potential:
$$
\phi =−U \left(r+\frac{a^3}...
2
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1
answer
35
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Does viscosity increase temperature of a fluid at the cost of macroscopic kinetic energy?
Viscosity on molecular level can be stated as a transfer of momentum from fast moving layers to slow moving layers through random molecular collisions. So can we state that (in case of no external ...
user366132
2
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answers
34
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Throwing near-boling water into minus 20C air
I have observed my daughter throw a flask of near-boiling water into the air outside at -20C. The water appears to turn into "steam" which actually appears to be ice crystals. She also tried ...
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Why can I hear when my shower gets hot?
I noticed recently that when I turn on my shower, I can hear the moment that the water heats up. The hissing sound gets slightly louder and its pitch changes. The pressure doesn't noticeably change ...
- 3,195
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27
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Nusselt number for developing turbulent flow
I need to develop a uniform method to cool a plate 1 degree, our idea was to let helium flow under it to transfer heat via convection. I concluded by some calculations that the Nusselt number for ...
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Thrust on container due to effluxing fluid
we know that by F=dP/dt=vdm/dt=pav^2
where p is density and P is momentum.considering the hole really small compared to the container.
however by Bernoullis equation
Pressure(inside)= Presure(atm) + 1/...
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11
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What equation models the shear rate as a function of the cross-sectional height of a square channel in lamina flow?
I am trying to model how shear rate changes across the cross section of a square channel (in a microfluidic device), depending on the height+width, fluid viscosity (assuming water) given it is fully ...
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22
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How to (coarsely) estimate turbulent kinetic energy (TKE) dissipation in a large tank?
I'm wondering if it is possible to say something semi-quantitative (approximate order of magnitude) about turbulent kinetic energy (TKE) dissipation in a large tank of water (6 m tall, 3 m wide). The ...
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2
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68
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Doubt with Heat and Potential Energy. (Warning: Many Assumptions) [closed]
I had a question in my Textbook which reads as follows,
Before that, we have to assume that the flowing water is ideal.
So, here we have to equate Change in Potential Energy to Heat Energy/Internal ...
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15
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Measuring a fluid's temperature using video of a drop falling into the fluid
Katie Bouman's PhD thesis begins with the following paragraph:
Watching a raindrop fall into a puddle of water, causing a ring of
expanding ripples, may seem mundane. However, behind this commonplace
...
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Is the Mach cone the model of a shockwave?
I am in the process of writing a mathematics paper which aims to model the interaction of a supersonic (or transonic for that matter) object with a flat plane. I need to determine the shape that a ...
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Difference between Pressure Jump and Pressure Gradient in multiphase flow, and Relationship between them
Assuming we have a multiphase flow (maybe a bubble immersed in water) with interface separating between the two phases. The interface is defined with a certain surface tension. Due to the liquid ...
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High-performance liquid chromatography (HPLC) injection
While practicing with high-performance liquid chromatography (HPLC), my lecturer asked me to inject the syringe slowly into six-port valve. She briefly explained that fast injection is disadvantageous ...
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Interaction of Supersonic and Hypersonic Objects
Lets imagine you are chilling in a plane cruising at some Mach 1 or Mach 2. Behind you, parallel with your direction a Mach 11 missile passes you by. What would you experience? Would you experience ...
- 904
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Can the turbulent viscosity in Large Eddy Simulation (LES) be taken out of the derivative for compressible flows?
I am working on Large Eddy Simulation (LES) for compressible flows and using the Smagorinsky model to compute the turbulent viscosity $\nu_t$.
In the filtered Navier-Stokes equations for compressible ...
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Would an object floating on a very low dense object go away by the force of air resistance?
Suppose that you have an object that is floating on the surface of a fluid. If the fluids viscosity was low enough, would normal air have enough drag to make it go away flying?
If it would, how would ...
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Does Bernoulli's Equation make Wind Tunnels Inaccurate?
From what I understand, Bernoulli's equation should be applied in the reference frame of still fluid.
Using Bernoulli's equation to a wind tunnel, we find that the pressure inside a wind tunnel should ...
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Extrapolating Missing Water Level Gage Data - Best Method
I'm interested in what would be the best method to extrapolate what may have been the peak surge elevation given some amount of data and a missing peak value due to the water level gage having topped ...
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Bernoulli's Equation + Conservation of Mass
In the following example am I allowed to assume the velocity of point (1) is zero?
my argument for this is that since $D_{tank}>>D_{tube}$ therefore by writing the continuity equation or ...
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0
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45
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Fluid dynamics in Newtonian regime from action
I struggle to understand how one can get the Euler, continuity and Poisson equation describing a fluid in the weak gravity regime from the Einstein-Hilbert plus fluid matter action. Say I start from
$$...
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1
answer
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Energy exchange between particle species in gravitational systems
Consider a gravitational system consisting of two different particle species.
Particle 1 only interacts gravitationally. Particle 2 interacts gravitationally and via some short-range force such that ...
- 1,354
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1
answer
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Why can't choked flow accelerate?
Why can't flow accelerate in the choked condition?
I think the best way to explain my question is through an example, so here it is:
Imagine you have $2$ boxes connected with a valve that is closed. ...
- 355
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26
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Torque Create by a propeller
I am working in a robotics project for a holomonic Drone, and I am having some difficulties understanding how a propeller generate thrust.
My robot currently has 6 motors + rotors, all the motor are ...
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2
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60
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Can Shear-Stress Cause Translation Motion? If Not, Why is There a Viscous Term in the Navier-Stokes Equations?
Something has recently begun to trouble me, specifically, the presence of the viscous shear term - ie $\mu \nabla^2 \mathbf{u}$ - in the Navier-Stokes equations.
I'm somewhat troubled by the presence ...
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1
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66
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Is Stress a Derivative?
On page 289 of the text "Fundamentals of Fluid Mechanics" by Munson et al., the authors give the following definition of the normal stress acting on the surface of a fluid element:
At any ...
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2
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97
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How to draw the Coriolis force in 2D?
I'm studying Geophysical fluid dynamics, especially the Coriolis force.
Now, in my book, this force$^{1}$ is defined as:
$$ \vec{F_c} = -fv \hat{x} + fu \hat{y} $$
where ($u,v$) are the components of ...
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Frank White's Fluid Mechanics pressure work derivation
So I have been trying to get my head around the derivation given by Frank White in his Fluid Mechanics book on pressure work (page 164,. He states that for mass going into the control volume, $$d\dot{...
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Drag force equation using the pressure distribution in fluid dynamics
I want to obtain the drag force equation for a flow around a cylinder.
Starting with the definition of pressure:
$${\displaystyle d\mathbf {F} _{n}=-p\,d\mathbf {A} =-p\,\mathbf {n} \,dA.}\tag1$$
...
- 904
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Explosions in high viscosity liquids
I was watching The Score (2001) in which De Niro manages to make a hole in a cobalt and titanium infused steel safe. he fills it with water. inserts an explosive and boom! the safe is open.
It made me ...
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Von Kármán momentum integral explanation
The Von Kármán momentum integral is the equation
$${\displaystyle {\frac {\tau _{w}}{\rho U^{2}}}={\frac {1}{U^{2}}}{\frac {\partial }{\partial t}}(U\delta _{1})+{\frac {\partial \delta _{2}}{\partial ...
- 904
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Displacement thickness derivation in the Von Kármán momentum integral
The Von Kármán momentum integral is
$${\displaystyle {\frac {\tau _{w}}{\rho U^{2}}}={\frac {1}{U^{2}}}{\frac {\partial }{\partial t}}(U\delta _{1})+{\frac {\partial \delta _{2}}{\partial x}}+{\frac {...
- 904
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1
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Using bernoulli's equation in a siphon doesn't work out?
I was thinking about doing a simple siphon experiment for my physics project like the follwing image:
The problem is, I can't calculate the flow rate of water in this situation - I used bernoulli's ...
- 3
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1
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42
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Explicit time-dependence of pressure in steady flow
In the textbook "Elementary Fluid Mechanics" by D.J. Acheson (Section 1.2), steady flow is defined by the equation $\frac{\partial \textbf{u}}{\partial t} = 0$, where $\textbf{u}(x, t)$ is ...
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