Questions tagged [fluid-dynamics]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
32
votes
3answers
4k views

Why does Coriolis determine the rotation direction of a cyclone but not my drain?

It is a common misconception that Coriolis is responsible for the direction the water swirls down a toilet, tub or sink drain. E.g. does a toilet flush the other way in the southern hemisphere? (If ...
16
votes
2answers
3k views

Why is aerodynamic resistance defined inversely?

When I think of wind resistance, I always think of the friction co-efficient, in $\mathrm{ms^{-1}}$, because that's always the way that it was presented in highschool and undergraduate physics. But ...
11
votes
1answer
1k views

What is the difference between an inertial instability and a symmetric instability?

Inertial and symmetric instabilities are fluid instabilities present in atmosphere and ocean. What are the difference between an inertial instability and a symmetric instability?
8
votes
1answer
141 views

Unrealistic solution for advection-diffusion-reaction PDE with heterogeneous porous media

About the code: I have a code which simulates concentration from advection-diffusion-reaction PDE in 2D space (X,Y) with time. The solution is obtained using fully implicit finite-difference method ...
6
votes
0answers
112 views

Shallow water height as vertical coordinate

In atmospheric physics we use often a variety of vertical coordinates, $z$ the height above some reference surface, or $r$ as distance from the planetary center. However sometimes it simplifies the ...
5
votes
3answers
148 views

coriolis force in atmospheric/ocean modeling

The Coriolis force is not a real force, but depending on the reference system and how it does refer to an inertial system. Could this Coriolis force as widely used in atmospheric/climate modeling be ...
4
votes
1answer
149 views

Why would geostrophic theory be invoked in the tropics with regards to the MJO?

In this paper reviewing the Madden-Julian Oscillation, frequently geostrophic theory (or approximately geostrophic) is often invoked. However, for geostrophic theory to be invoked, $$Ro=\frac{U}{f_0L}&...
4
votes
1answer
131 views

comparing use of Laplace equation with diffusion equation to simulate flow of fluid/water through porous media?

What is the difference in using Laplace equation (say only in 1D) to simulate water flow in a porous media with that of using diffusion equation for same purpose?
4
votes
0answers
36 views

Over what scales can we begin to apply fluid dynamics to accurately model properties of the mantle?

Over what size temporal/spatial scales do geophysicists and geodynamicists begin to apply fluid dynamics to model the mantle rather than elastic/plastic deformation theory?
4
votes
0answers
235 views

What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics?

What is the difference between the Hydraulic diffusion equation and the Richards equation in groundwater dynamics? I want also to understand the difference between the different storage coefficients (...
3
votes
1answer
235 views

How to characterize flow of nonreactive tracer in a porous media?

About Tracer Experiment This experiment is conducted by injecting a fluid with nonreactive species of certain concentration inside a column or core composed of sand. The injection of fluid can either ...
3
votes
1answer
57 views

What forms do groundwater flow equations have when Dupuit supposition is not considered?

Near pumping wells or near/beneath a stream, the groundwater flow is not totally horizontal and the vertical component of groundwater movement at these points cannot be ignored in reality. Often, ...
3
votes
0answers
55 views

Godfrey's island rule (stream function in multiply connected domains)

In this paper, the authors detail the methods to calculate the stream function $\psi$ from velocity data in the case of the global ocean (i.e., multiply connected domains). The general idea is to use ...
3
votes
0answers
47 views

Link between different ways of modeling permeability

The most famous equation describing the permeability $k$ of a soil is the Kozeny-Carman equation: $$k = \frac{\phi}{8}r^2 \approx \frac{\phi}{c}\left(\frac{V}{S}\right)^2$$ $\phi$: porosity V: pore ...
2
votes
1answer
55 views

At what point are water droplets too small to make a rainbow?

This question asks How to tell if fog is made out of water droplets or ice crystals? I know that ice fog makes a rainbow where fog does not. Ice crystals aside: How does the water droplet size ...
2
votes
1answer
124 views

What affects the surface characteristics of cumulus clouds?

I love looking at clouds. I love trying to describe them and compare what I see day to day. I have dozens of questions about the things I’ve observed and I would really like to understand the physics ...
2
votes
0answers
46 views

Reasons for choosing LES in stead of RANS models?

In oceanography, is there any particular reason why choosing large eddy simulations in stead of RANS (regardless of the type of flow)? In both cases, 2d simulations would be used (shallow water model)....
1
vote
1answer
57 views

Hydrology- flow accumulation

I'm not specialist in hydrology, and I would be very grateful if you answer my question: What is flow accumulation in hydrology? Why algorithms used to calculate it over a raster DEM don't take ...
1
vote
1answer
45 views

Barotropic vorticity equation

I came across the barotropic vorticity equation (below) in Sakamoto (2002) and I cannot figure it out. The notation is not clear to me. How can it be derived from the Navier-Stokes equation? $$ \beta\...
1
vote
0answers
21 views

Algorithm for anisotropic porous media reconstruction

I have a series of micro-tomography images of a porous material (received from experimental partners) with a resolution 10 $\mu m$ with total size 1cm $\times$ 1cm. Porosity of the porous material ...