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# Questions tagged [fluid-dynamics]

The quantitative study of how fluids (gases and liquids) move.

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### In a fluid flow, how do you tell if negative acceleration is deceleration or change in direction?

When solving for the acceleration of a fluid flow, you use the equation: (∂u/∂t)+u(∂u/∂x)+v(∂u/∂y). If the solution at a given u and v are negative, how do you know if the flow has a negative ...
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### Name of viscosity formula? [closed]

I am doing a school project comparing viscosity of different brands of honey. The easiest way for me to test viscosity was dropping a ball bearing down a grad cylinder filled with honey. So I used ...
1 vote
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### Freedoms in non-dimensionalization of Navier-Stokes equation and their usage in normalization

When we non-dimensionalize NS equation, we typically take some characteristic scales of length, velocity etc, say the size of the box, average speed of the fluid in the flow direction etc. Once we ...
1 vote
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### Two ways of non-dimensionalizing Navier Stokes equation

I can see two ways of non-dimensionalizing Navier Stokes equation. One of them is from Wikipedia where one can see that the non-dimensionalization is performed by taking $p^*=\frac{p}{\rho U^2}$ where ...
11 views

### How can i model natural convection over vertical surface using the Boussinesq approximation?

How can I utilize the Boussinesq approximation and Finite Difference Method (FDM) to model natural convection in a wall where the bottom temperature is higher and the top temperature is lower?
1 vote
31 views

### How does length effect drag?

Section of pipe: 20mm diameter, 2000mm length, hemisphere end cap. Moving horizontally through water, I think that the coefficient of drag would be approx. 0.42. How would the length of the pipe ...
13 views

### What is the name and notation given to the inverse of the inertial resistivity $\beta$ (aka non-Darcy factor or Forchhiemer factor)?

The viscous resistivity $\alpha$ is the reciprocal of permeability $k$. That is, $\alpha=1/k$. Considering the 1D isotropic non-Darcy equation, $$\tag{1} -\frac{dp}{dx}=\alpha \mu q+ \beta \rho q^2,$$...
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### Is there an algorithm for real-time fluid simulations with Fluid-structure interaction with viscous fluids?

I'm trying to write a Fluid simulator for my school coding project. I want the Fluid simulator to be able to handle FSI with viscous Fluids in real-time and be 3D. I've been reading a few papers and ...
1 vote
51 views

### How can I derive this thermodynamically equivalent expression for the speed of sound?

Background In Viscous Fluid Flow by White, the speed of sound for a gas is given as $$\tag{1-71} a^2 = \frac{\partial p}{\partial \rho}\big|_s$$ where the partial derivative is computed at constant ...
83 views

### What causes drag crisis?

While reading the Wikipedia article on Drag Crisis, I found: The drag crisis is associated with a transition from laminar to turbulent boundary layer flow adjacent to the object. While, the ...
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1 vote
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### Why dows Water in the shower run down glass pane in meanders?

The last days I noticed that after taking a shower (cabin has glass walls, safety glass if it matters) and finally splashing the glass panes for cleaning soap residues off, some of the remaining water ...
51 views

### Interchange of Lagrangian/material derivative and volume integral

In hydrodynamics there are two basic approaches. The first is the Eulerian specification where the coordinate system is fixed. In that case, the partial time derivative and volume integral operators ...
1 vote
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### Forces On Toroidal Wind Tunnel wihen Wing is attached inside? [closed]

Consider the attached Toroidal wind Tunnel. The Wind tunnel is in Vacuum and the moving air and the attached wing are only inside the toroidal tunnel. Will the mounted wing on the walls of the tunnel ...
1 vote
32 views

### Airflow between two rooms (one hot, one cold) [closed]

Scenario — It is night time and somewhat cold outside. Room 1 (Bedroom): The window is slightly creaked open. I have a space heater going on continually heating room 1. One door is closed to the ...
36 views

### Can irreversibility arise from systems that are microscopically reversible? [duplicate]

I was reading about Feynman's sprinkler problem, and came across a paper that discussed irreversibility in ideal fluids. It quoted the fact that When a real fluid is expelled quickly from a tube, it ...
80 views

### Time dependence in Eulerian description of fluid flow

In the Eulerian description of velocity field, suppose $x,y,z$ are fixed coordinates, the velocity at that point at time $t$ is $\mathbf{u}(x,y,z,t)$. I am confused whether $x,y,z$ depend on time or ...
46 views

### Fluid compression against wall

A compressible fluid within a fixed cubic container is compressed at time $t=0$ by a spatially homogeneous force against one face of the cube. After a long time the mass distribution of the fluid ...
If I have a fluid in motion at a given time and I know its pressure $p$ everywhere, I know its dynamic viscosity $\mu$ and I know its velocity field $\vec V$. This system must hold some intrinsic ...