4
votes
2answers
71 views

Are Mach Diamonds radially symmetrical?

Videos like this show a form that suggests a radial symmetry in the gas jet. The same is reinforced by schematic illustrations. But other images, like this, look like there is a twisting structure ...
7
votes
4answers
312 views

Conserved quantities and total derivatives?

I am having a bit of a crisis in understanding of the physical meanings of total derivatives. When a quantity $\rho$ (be it a vector or a scalar) is said to be conserved, then (mathematically) ...
1
vote
1answer
56 views

Convective derivative of oscillating fluid with bulk motion?

I have a fluid $u$, which comprises a zeroth order constant motion $u_0$ as well as a first order oscillatory motion $u_1$. The convective derivative is $$\frac{\partial u}{\partial t} ...
0
votes
1answer
70 views

Why is the collision term negative in the equation of motion for a fluid of electrons in a plasma?

The fluid equation of motion for electrons in a cold plasma is \begin{equation} m_en_e\frac{d\textbf{v}}{dt} = -en_e(\textbf{E}+\textbf{v}\times \textbf{B}) - m_en_e\nu\textbf{v} \end{equation} where ...
2
votes
1answer
155 views

Application of plasma actuators for flow control of moving objects

I've recently been to a converence on plasma physics were, to my surprise, a lot of presentations were concerned with plasma actuator. Could someone, preferably in the field, tell me how long people ...
5
votes
1answer
276 views

What causes the structure visible in first few milliseconds of a nuclear explosion?

Following on from this question, here is a high-speed photograph of a nuclear explosion, taken about 1 ms after detonation: (source) As anna v pointed out, several similar images can be seen in a ...
3
votes
1answer
193 views

What velocity must an aircraft achieve for its shock wave to transform to plasma?

A follow-up to After what speed air friction starts to heat up an object? I understand there may be technological limitations at present ... but, is it theoretically possible for a body to travel ...